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Sample records for lh2 excited state

  1. Evidence of excited state localization and static disorder in LH2 investigated by 2D-polarization single-molecule imaging at room temperature.

    PubMed

    Tubasum, Sumera; Camacho, Rafael; Meyer, Matthias; Yadav, Dheerendra; Cogdell, Richard J; Pullerits, Tõnu; Scheblykin, Ivan G

    2013-12-01

    Two-dimensional polarization fluorescence imaging of single light harvesting complexes 2 (LH2) of Rps. acidophila was carried out to investigate the polarization properties of excitation and fluorescence emission simultaneously, at room temperature. In two separate experiments we excited LH2 with a spectrally narrow laser line matched to the absorption bands of the two chromophore rings, B800 and B850, thereby indirectly and directly triggering fluorescence of the B850 exciton state. A correlation analysis of the polarization modulation depths in excitation and emission for a large number of single complexes was performed. Our results show, in comparison to B800, that the B850 ring is a more isotropic absorber due to the excitonic nature of its excited states. At the same time, we observed a strong tendency for LH2 to emit with dipolar character, from which preferential localization of the emissive exciton, stable for minutes, is inferred. We argue that the observed effects can consistently be explained by static energetic disorder and/or deformation of the complex, with possible involvement of exciton self-trapping.

  2. Single-molecule spectroscopy reveals photosynthetic LH2 complexes switch between emissive states

    PubMed Central

    Schlau-Cohen, Gabriela S.; Wang, Quan; Southall, June; Cogdell, Richard J.; Moerner, W. E.

    2013-01-01

    Photosynthetic organisms flourish under low light intensities by converting photoenergy to chemical energy with near unity quantum efficiency and under high light intensities by safely dissipating excess photoenergy and deleterious photoproducts. The molecular mechanisms balancing these two functions remain incompletely described. One critical barrier to characterizing the mechanisms responsible for these processes is that they occur within proteins whose excited-state properties vary drastically among individual proteins and even within a single protein over time. In ensemble measurements, these excited-state properties appear only as the average value. To overcome this averaging, we investigate the purple bacterial antenna protein light harvesting complex 2 (LH2) from Rhodopseudomonas acidophila at the single-protein level. We use a room-temperature, single-molecule technique, the anti-Brownian electrokinetic trap, to study LH2 in a solution-phase (nonperturbative) environment. By performing simultaneous measurements of fluorescence intensity, lifetime, and spectra of single LH2 complexes, we identify three distinct states and observe transitions occurring among them on a timescale of seconds. Our results reveal that LH2 complexes undergo photoactivated switching to a quenched state, likely by a conformational change, and thermally revert to the ground state. This is a previously unobserved, reversible quenching pathway, and is one mechanism through which photosynthetic organisms can adapt to changes in light intensities. PMID:23776245

  3. Single-molecule spectroscopy reveals photosynthetic LH2 complexes switch between emissive states.

    PubMed

    Schlau-Cohen, Gabriela S; Wang, Quan; Southall, June; Cogdell, Richard J; Moerner, W E

    2013-07-01

    Photosynthetic organisms flourish under low light intensities by converting photoenergy to chemical energy with near unity quantum efficiency and under high light intensities by safely dissipating excess photoenergy and deleterious photoproducts. The molecular mechanisms balancing these two functions remain incompletely described. One critical barrier to characterizing the mechanisms responsible for these processes is that they occur within proteins whose excited-state properties vary drastically among individual proteins and even within a single protein over time. In ensemble measurements, these excited-state properties appear only as the average value. To overcome this averaging, we investigate the purple bacterial antenna protein light harvesting complex 2 (LH2) from Rhodopseudomonas acidophila at the single-protein level. We use a room-temperature, single-molecule technique, the anti-Brownian electrokinetic trap, to study LH2 in a solution-phase (nonperturbative) environment. By performing simultaneous measurements of fluorescence intensity, lifetime, and spectra of single LH2 complexes, we identify three distinct states and observe transitions occurring among them on a timescale of seconds. Our results reveal that LH2 complexes undergo photoactivated switching to a quenched state, likely by a conformational change, and thermally revert to the ground state. This is a previously unobserved, reversible quenching pathway, and is one mechanism through which photosynthetic organisms can adapt to changes in light intensities.

  4. Single-molecule spectroscopy unmasks the lowest exciton state of the B850 assembly in LH2 from Rps. acidophila.

    PubMed

    Kunz, Ralf; Timpmann, Kõu; Southall, June; Cogdell, Richard J; Freiberg, Arvi; Köhler, Jürgen

    2014-05-01

    We have recorded fluorescence-excitation and emission spectra from single LH2 complexes from Rhodopseudomonas (Rps.) acidophila. Both types of spectra show strong temporal spectral fluctuations that can be visualized as spectral diffusion plots. Comparison of the excitation and emission spectra reveals that for most of the complexes the lowest exciton transition is not observable in the excitation spectra due to the cutoff of the detection filter characteristics. However, from the spectral diffusion plots we have the full spectral and temporal information at hand and can select those complexes for which the excitation spectra are complete. Correlating the red most spectral feature of the excitation spectrum with the blue most spectral feature of the emission spectrum allows an unambiguous assignment of the lowest exciton state. Hence, application of fluorescence-excitation and emission spectroscopy on the same individual LH2 complex allows us to decipher spectral subtleties that are usually hidden in traditional ensemble spectroscopy.

  5. Single-Molecule Spectroscopy Unmasks the Lowest Exciton State of the B850 Assembly in LH2 from Rps. acidophila

    PubMed Central

    Kunz, Ralf; Timpmann, Kõu; Southall, June; Cogdell, Richard J.; Freiberg, Arvi; Köhler, Jürgen

    2014-01-01

    We have recorded fluorescence-excitation and emission spectra from single LH2 complexes from Rhodopseudomonas (Rps.) acidophila. Both types of spectra show strong temporal spectral fluctuations that can be visualized as spectral diffusion plots. Comparison of the excitation and emission spectra reveals that for most of the complexes the lowest exciton transition is not observable in the excitation spectra due to the cutoff of the detection filter characteristics. However, from the spectral diffusion plots we have the full spectral and temporal information at hand and can select those complexes for which the excitation spectra are complete. Correlating the red most spectral feature of the excitation spectrum with the blue most spectral feature of the emission spectrum allows an unambiguous assignment of the lowest exciton state. Hence, application of fluorescence-excitation and emission spectroscopy on the same individual LH2 complex allows us to decipher spectral subtleties that are usually hidden in traditional ensemble spectroscopy. PMID:24806933

  6. Fluorescence-excitation and emission spectra from LH2 antenna complexes of Rhodopseudomonas acidophila as a function of the sample preparation conditions.

    PubMed

    Kunz, Ralf; Timpmann, Kõu; Southall, June; Cogdell, Richard J; Köhler, Jürgen; Freiberg, Arvi

    2013-10-10

    The high sensitivity of optical spectra of pigment-protein complexes to temperature and pressure is well known. In the present study, we have demonstrated the significant influence of the environments commonly used in bulk and single-molecule spectroscopic studies at low temperatures on the LH2 photosynthetic antenna complex from Rhodopseudomonas acidophila. A transfer of this LH2 complex from a bulk-buffer solution into a spin-coated polymer film results in a 189 cm(-1) blue shift of the B850 excitonic absorption band at 5 K. Within the molecular exciton model, the origin of this shift could be disentangled into three parts, namely to an increase of the local site energies, a contraction of the exciton band, and a decrease of the displacement energy.

  7. LH2 airport requirements study

    NASA Technical Reports Server (NTRS)

    Brewer, G. D. (Editor)

    1976-01-01

    A preliminary assessment of the facilities and equipment which will be required at a representative airport is provided so liquid hydrogen LH2 can be used as fuel in long range transport aircraft in 1995-2000. A complete facility was conceptually designed, sized to meet the projected air traffic requirement. The facility includes the liquefaction plant, LH2, storage capability, and LH2 fuel handling system. The requirements for ground support and maintenance for the LH2 fueled aircraft were analyzed. An estimate was made of capital and operating costs which might be expected for the facility. Recommendations were made for design modifications to the reference aircraft, reflecting results of the analysis of airport fuel handling requirements, and for a program of additional technology development for air terminal related items.

  8. Carotenoid-bacteriochlorophyll energy transfer in LH2 complexes studied with 10-fs time resolution.

    PubMed

    Polli, Dario; Cerullo, Giulio; Lanzani, Guglielmo; De Silvestri, Sandro; Hashimoto, Hideki; Cogdell, Richard J

    2006-04-01

    In this report, we present a study of carotenoid-bacteriochlorophyll energy transfer processes in two peripheral light-harvesting complexes (known as LH2) from purple bacteria. We use transient absorption spectroscopy with approximately 10 fs temporal resolution, which is necessary to observe the very fast energy relaxation processes. By comparing excited-state dynamics of the carotenoids in organic solvents and inside the LH2 complexes, it has been possible to directly evaluate their energy transfer efficiency to the bacteriochlorophylls. In the case of okenone in the LH2 complex from Chromatium purpuratum, we obtained an energy transfer efficiency of etaET2=63+/-2.5% from the optically active excited state (S2) and etaET1=61+/-2% from the optically dark state (S1); for rhodopin glucoside contained in the LH2 complex from Rhodopseudomonas acidophila these values become etaET2=49.5+/-3.5% and etaET1=5.1+/-1%. The measurements also enabled us to observe vibrational energy relaxation in the carotenoids' S1 state and real-time collective vibrational coherence initiated by the ultrashort pump pulses. Our results are important for understanding the dynamics of early events of photosynthesis and relating it to the structural arrangement of the chromophores.

  9. Direct visualization of exciton reequilibration in the LH1 and LH2 complexes of Rhodobacter sphaeroides by multipulse spectroscopy.

    PubMed

    Cohen Stuart, Thomas A; Vengris, Mikas; Novoderezhkin, Vladimir I; Cogdell, Richard J; Hunter, C Neil; van Grondelle, Rienk

    2011-05-01

    The dynamics of the excited states of the light-harvesting complexes LH1 and LH2 of Rhodobacter sphaeroides are governed, mainly, by the excitonic nature of these ring-systems. In a pump-dump-probe experiment, the first pulse promotes LH1 or LH2 to its excited state and the second pulse dumps a portion of the excited state. By selective dumping, we can disentangle the dynamics normally hidden in the excited-state manifold. We find that by using this multiple-excitation technique we can visualize a 400-fs reequilibration reflecting relaxation between the two lowest exciton states that cannot be directly explored by conventional pump-probe. An oscillatory feature is observed within the exciton reequilibration, which is attributed to a coherent motion of a vibrational wavepacket with a period of ∼150 fs. Our disordered exciton model allows a quantitative interpretation of the observed reequilibration processes occurring in these antennas.

  10. Direct Visualization of Exciton Reequilibration in the LH1 and LH2 Complexes of Rhodobacter sphaeroides by Multipulse Spectroscopy

    PubMed Central

    Cohen Stuart, Thomas A.; Vengris, Mikas; Novoderezhkin, Vladimir I.; Cogdell, Richard J.; Hunter, C. Neil; van Grondelle, Rienk

    2011-01-01

    The dynamics of the excited states of the light-harvesting complexes LH1 and LH2 of Rhodobacter sphaeroides are governed, mainly, by the excitonic nature of these ring-systems. In a pump-dump-probe experiment, the first pulse promotes LH1 or LH2 to its excited state and the second pulse dumps a portion of the excited state. By selective dumping, we can disentangle the dynamics normally hidden in the excited-state manifold. We find that by using this multiple-excitation technique we can visualize a 400-fs reequilibration reflecting relaxation between the two lowest exciton states that cannot be directly explored by conventional pump-probe. An oscillatory feature is observed within the exciton reequilibration, which is attributed to a coherent motion of a vibrational wavepacket with a period of ∼150 fs. Our disordered exciton model allows a quantitative interpretation of the observed reequilibration processes occurring in these antennas. PMID:21539791

  11. Ground-State Electronic Structure of RC-LH1 and LH2 Pigment Assemblies of Purple Bacteria via the EBF-MO Method.

    PubMed

    Shrestha, Kushal; Jakubikova, Elena

    2015-08-20

    Light-harvesting antennas are protein-pigment complexes that play a crucial role in natural photosynthesis. The antenna complexes absorb light and transfer energy to photosynthetic reaction centers where charge separation occurs. This work focuses on computational studies of the electronic structure of the pigment networks of light-harvesting complex I (LH1), LH1 with the reaction center (RC-LH1), and light-harvesting complex II (LH2) found in purple bacteria. As the pigment networks of LH1, RC-LH1, and LH2 contain thousands of atoms, conventional density functional theory (DFT) and ab initio calculations of these systems are not computationally feasible. Therefore, we utilize DFT in conjunction with the energy-based fragmentation with molecular orbitals method and a semiempirical approach employing the extended Hückel model Hamiltonian to determine the electronic properties of these pigment assemblies. Our calculations provide a deeper understanding of the electronic structure of natural light-harvesting complexes, especially their pigment networks, which could assist in rational design of artificial photosynthetic devices.

  12. Spectral heterogeneity and carotenoid-to-bacteriochlorophyll energy transfer in LH2 light-harvesting complexes from Allochromatium vinosum.

    PubMed

    Magdaong, Nikki M; LaFountain, Amy M; Hacking, Kirsty; Niedzwiedzki, Dariusz M; Gibson, George N; Cogdell, Richard J; Frank, Harry A

    2016-02-01

    Photosynthetic organisms produce a vast array of spectral forms of antenna pigment-protein complexes to harvest solar energy and also to adapt to growth under the variable environmental conditions of light intensity, temperature, and nutrient availability. This behavior is exemplified by Allochromatium (Alc.) vinosum, a photosynthetic purple sulfur bacterium that produces different types of LH2 light-harvesting complexes in response to variations in growth conditions. In the present work, three different spectral forms of LH2 from Alc. vinosum, B800-820, B800-840, and B800-850, were isolated, purified, and examined using steady-state absorption and fluorescence spectroscopy, and ultrafast time-resolved absorption spectroscopy. The pigment composition of the LH2 complexes was analyzed by high-performance liquid chromatography, and all were found to contain five carotenoids: lycopene, anhydrorhodovibrin, spirilloxanthin, rhodopin, and rhodovibrin. Spectral reconstructions of the absorption and fluorescence excitation spectra based on the pigment composition revealed significantly more spectral heterogeneity in these systems compared to LH2 complexes isolated from other species of purple bacteria. The data also revealed the individual carotenoid-to-bacteriochlorophyll energy transfer efficiencies which were correlated with the kinetic data from the ultrafast transient absorption spectroscopic experiments. This series of LH2 complexes allows a systematic exploration of the factors that determine the spectral properties of the bound pigments and control the rate and efficiency of carotenoid-to-bacteriochlorophyll energy transfer. PMID:26048106

  13. Spectral heterogeneity and carotenoid-to-bacteriochlorophyll energy transfer in LH2 light-harvesting complexes from Allochromatium vinosum.

    PubMed

    Magdaong, Nikki M; LaFountain, Amy M; Hacking, Kirsty; Niedzwiedzki, Dariusz M; Gibson, George N; Cogdell, Richard J; Frank, Harry A

    2016-02-01

    Photosynthetic organisms produce a vast array of spectral forms of antenna pigment-protein complexes to harvest solar energy and also to adapt to growth under the variable environmental conditions of light intensity, temperature, and nutrient availability. This behavior is exemplified by Allochromatium (Alc.) vinosum, a photosynthetic purple sulfur bacterium that produces different types of LH2 light-harvesting complexes in response to variations in growth conditions. In the present work, three different spectral forms of LH2 from Alc. vinosum, B800-820, B800-840, and B800-850, were isolated, purified, and examined using steady-state absorption and fluorescence spectroscopy, and ultrafast time-resolved absorption spectroscopy. The pigment composition of the LH2 complexes was analyzed by high-performance liquid chromatography, and all were found to contain five carotenoids: lycopene, anhydrorhodovibrin, spirilloxanthin, rhodopin, and rhodovibrin. Spectral reconstructions of the absorption and fluorescence excitation spectra based on the pigment composition revealed significantly more spectral heterogeneity in these systems compared to LH2 complexes isolated from other species of purple bacteria. The data also revealed the individual carotenoid-to-bacteriochlorophyll energy transfer efficiencies which were correlated with the kinetic data from the ultrafast transient absorption spectroscopic experiments. This series of LH2 complexes allows a systematic exploration of the factors that determine the spectral properties of the bound pigments and control the rate and efficiency of carotenoid-to-bacteriochlorophyll energy transfer.

  14. High Specific Power Motors in LN2 and LH2

    NASA Technical Reports Server (NTRS)

    Brown, Gerald V.; Jansen, Ralph H.; Trudell, Jeffrey J.

    2007-01-01

    A switched reluctance motor has been operated in liquid nitrogen (LN2) with a power density as high as that reported for any motor or generator. The high performance stems from the low resistivity of Cu at LN2 temperature and from the geometry of the windings, the combination of which permits steady-state rms current density up to 7000 A/cm2, about 10 times that possible in coils cooled by natural convection at room temperature. The Joule heating in the coils is conducted to the end turns for rejection to the LN2 bath. Minimal heat rejection occurs in the motor slots, preserving that region for conductor. In the end turns, the conductor layers are spaced to form a heat-exchanger-like structure that permits nucleate boiling over a large surface area. Although tests were performed in LN2 for convenience, this motor was designed as a prototype for use with liquid hydrogen (LH2) as the coolant. End-cooled coils would perform even better in LH2 because of further increases in copper electrical and thermal conductivities. Thermal analyses comparing LN2 and LH2 cooling are presented verifying that end-cooled coils in LH2 could be either much longer or could operate at higher current density without thermal runaway than in LN2.

  15. High Specific Power Motors in LN2 and LH2

    NASA Technical Reports Server (NTRS)

    Brown, Gerald V.; Jansen, Ralph H.; Trudell, Jeffrey J.

    2007-01-01

    A switched reluctance motor has been operated in liquid nitrogen (LN2) with a power density as high as that reported for any motor or generator. The high performance stems from the low resistivity of Cu at LN2 temperature and from the geometry of the windings, the combination of which permits steady-state rms current density up to 7000 A/sq cm, about 10 times that possible in coils cooled by natural convection at room temperature. The Joule heating in the coils is conducted to the end turns for rejection to the LN2 bath. Minimal heat rejection occurs in the motor slots, preserving that region for conductor. In the end turns, the conductor layers are spaced to form a heat-exchanger-like structure that permits nucleate boiling over a large surface area. Although tests were performed in LN2 for convenience, this motor was designed as a prototype for use with liquid hydrogen (LH2) as the coolant. End-cooled coils would perform even better in LH2 because of further increases in copper electrical and thermal conductivities. Thermal analyses comparing LN2 and LH2 cooling are presented verifying that end-cooled coils in LH2 could be either much longer or could operate at higher current density without thermal runaway than in LN2.

  16. Synchronous Measurement of Ultrafast Anisotropy Decay of the B850 in Bacterial LH2 Complex

    NASA Astrophysics Data System (ADS)

    Wang, Yun-Peng; Du, Lu-Chao; Zhu, Gang-Bei; Wang, Zhuan; Weng, Yu-Xiang

    2015-02-01

    Ultrafast anisotropic decay is a prominent parameter revealing ultrafast energy and electron transfer; however, it is difficult to be determined reliably owing to the requirement of a simultaneous availability of the parallel and perpendicular polarized decay kinetics. Nowadays, any measurement of anisotropic decay is a kind of approach to the exact simultaneity. Here we report a novel method for a synchronous ultrafast anisotropy decay measurement, which can well determine the anisotropy, even at a very early time, as the rising phase of the excitation laser pulse. The anisotropic decay of the B850 in bacterial light harvesting antenna complex LH2 of Rhodobacter sphaeroides in solution at room temperature with coherent excitation is detected by this method, which shows a polarization response time of 30 fs, and the energy transfer from the initial excitation to the bacteriochlorophylls in B850 ring takes about 70 fs. The anisotropic decay that is probed at the red side of the absorption spectrum, such as 880 nm, has an initial value of 0.4, corresponding to simulated emission, while the blue side with an anisotropy of 0.1 contributes to the ground-state bleaching. Our results show that the coherent excitation covering the whole ring might not be realized owing to the symmetry breaking of LH2: from C9 symmetry in membrane to C2 symmetry in solution.

  17. Fluorescence polarization measures energy funneling in single light-harvesting antennas--LH2 vs conjugated polymers.

    PubMed

    Camacho, Rafael; Tubasum, Sumera; Southall, June; Cogdell, Richard J; Sforazzini, Giuseppe; Anderson, Harry L; Pullerits, Tõnu; Scheblykin, Ivan G

    2015-10-19

    Numerous approaches have been proposed to mimic natural photosynthesis using artificial antenna systems, such as conjugated polymers (CPs), dendrimers, and J-aggregates. As a result, there is a need to characterize and compare the excitation energy transfer (EET) properties of various natural and artificial antennas. Here we experimentally show that EET in single antennas can be characterized by 2D polarization imaging using the single funnel approximation. This methodology addresses the ability of an individual antenna to transfer its absorbed energy towards a single pool of emissive states, using a single parameter called energy funneling efficiency (ε). We studied individual peripheral antennas of purple bacteria (LH2) and single CP chains of 20 nm length. As expected from a perfect antenna, LH2s showed funneling efficiencies close to unity. In contrast, CPs showed lower average funneling efficiencies, greatly varying from molecule to molecule. Cyclodextrin insulation of the conjugated backbone improves EET, increasing the fraction of CPs possessing ε = 1. Comparison between LH2s and CPs shows the importance of the protection systems and the protein scaffold of LH2, which keep the chromophores in functional form and at such geometrical arrangement that ensures excellent EET.

  18. Fluorescence polarization measures energy funneling in single light-harvesting antennas—LH2 vs conjugated polymers

    NASA Astrophysics Data System (ADS)

    Camacho, Rafael; Tubasum, Sumera; Southall, June; Cogdell, Richard J.; Sforazzini, Giuseppe; Anderson, Harry L.; Pullerits, Tõnu; Scheblykin, Ivan G.

    2015-10-01

    Numerous approaches have been proposed to mimic natural photosynthesis using artificial antenna systems, such as conjugated polymers (CPs), dendrimers, and J-aggregates. As a result, there is a need to characterize and compare the excitation energy transfer (EET) properties of various natural and artificial antennas. Here we experimentally show that EET in single antennas can be characterized by 2D polarization imaging using the single funnel approximation. This methodology addresses the ability of an individual antenna to transfer its absorbed energy towards a single pool of emissive states, using a single parameter called energy funneling efficiency (ɛ). We studied individual peripheral antennas of purple bacteria (LH2) and single CP chains of 20 nm length. As expected from a perfect antenna, LH2s showed funneling efficiencies close to unity. In contrast, CPs showed lower average funneling efficiencies, greatly varying from molecule to molecule. Cyclodextrin insulation of the conjugated backbone improves EET, increasing the fraction of CPs possessing ɛ = 1. Comparison between LH2s and CPs shows the importance of the protection systems and the protein scaffold of LH2, which keep the chromophores in functional form and at such geometrical arrangement that ensures excellent EET.

  19. Fluorescence polarization measures energy funneling in single light-harvesting antennas—LH2 vs conjugated polymers

    PubMed Central

    Camacho, Rafael; Tubasum, Sumera; Southall, June; Cogdell, Richard J.; Sforazzini, Giuseppe; Anderson, Harry L.; Pullerits, Tõnu; Scheblykin, Ivan G.

    2015-01-01

    Numerous approaches have been proposed to mimic natural photosynthesis using artificial antenna systems, such as conjugated polymers (CPs), dendrimers, and J-aggregates. As a result, there is a need to characterize and compare the excitation energy transfer (EET) properties of various natural and artificial antennas. Here we experimentally show that EET in single antennas can be characterized by 2D polarization imaging using the single funnel approximation. This methodology addresses the ability of an individual antenna to transfer its absorbed energy towards a single pool of emissive states, using a single parameter called energy funneling efficiency (ε). We studied individual peripheral antennas of purple bacteria (LH2) and single CP chains of 20 nm length. As expected from a perfect antenna, LH2s showed funneling efficiencies close to unity. In contrast, CPs showed lower average funneling efficiencies, greatly varying from molecule to molecule. Cyclodextrin insulation of the conjugated backbone improves EET, increasing the fraction of CPs possessing ε = 1. Comparison between LH2s and CPs shows the importance of the protection systems and the protein scaffold of LH2, which keep the chromophores in functional form and at such geometrical arrangement that ensures excellent EET. PMID:26478272

  20. High Efficiency Light Harvesting by Carotenoids in the LH2 Complex from Photosynthetic Bacteria: Unique Adaptation to Growth under Low-Light Conditions

    PubMed Central

    2015-01-01

    Rhodopin, rhodopinal, and their glucoside derivatives are carotenoids that accumulate in different amounts in the photosynthetic bacterium, Rhodoblastus (Rbl.) acidophilus strain 7050, depending on the intensity of the light under which the organism is grown. The different growth conditions also have a profound effect on the spectra of the bacteriochlorophyll (BChl) pigments that assemble in the major LH2 light-harvesting pigment–protein complex. Under high-light conditions the well-characterized B800-850 LH2 complex is formed and accumulates rhodopin and rhodopin glucoside as the primary carotenoids. Under low-light conditions, a variant LH2, denoted B800-820, is formed, and rhodopinal and rhodopinal glucoside are the most abundant carotenoids. The present investigation compares and contrasts the spectral properties and dynamics of the excited states of rhodopin and rhodopinal in solution. In addition, the systematic differences in pigment composition and structure of the chromophores in the LH2 complexes provide an opportunity to explore the effect of these factors on the rate and efficiency of carotenoid-to-BChl energy transfer. It is found that the enzymatic conversion of rhodopin to rhodopinal by Rbl. acidophilus 7050 grown under low-light conditions results in nearly 100% carotenoid-to-BChl energy transfer efficiency in the LH2 complex. This comparative analysis provides insight into how photosynthetic systems are able to adapt and survive under challenging environmental conditions. PMID:25171303

  1. High efficiency light harvesting by carotenoids in the LH2 complex from photosynthetic bacteria: unique adaptation to growth under low-light conditions.

    PubMed

    Magdaong, Nikki M; LaFountain, Amy M; Greco, Jordan A; Gardiner, Alastair T; Carey, Anne-Marie; Cogdell, Richard J; Gibson, George N; Birge, Robert R; Frank, Harry A

    2014-09-25

    Rhodopin, rhodopinal, and their glucoside derivatives are carotenoids that accumulate in different amounts in the photosynthetic bacterium, Rhodoblastus (Rbl.) acidophilus strain 7050, depending on the intensity of the light under which the organism is grown. The different growth conditions also have a profound effect on the spectra of the bacteriochlorophyll (BChl) pigments that assemble in the major LH2 light-harvesting pigment-protein complex. Under high-light conditions the well-characterized B800-850 LH2 complex is formed and accumulates rhodopin and rhodopin glucoside as the primary carotenoids. Under low-light conditions, a variant LH2, denoted B800-820, is formed, and rhodopinal and rhodopinal glucoside are the most abundant carotenoids. The present investigation compares and contrasts the spectral properties and dynamics of the excited states of rhodopin and rhodopinal in solution. In addition, the systematic differences in pigment composition and structure of the chromophores in the LH2 complexes provide an opportunity to explore the effect of these factors on the rate and efficiency of carotenoid-to-BChl energy transfer. It is found that the enzymatic conversion of rhodopin to rhodopinal by Rbl. acidophilus 7050 grown under low-light conditions results in nearly 100% carotenoid-to-BChl energy transfer efficiency in the LH2 complex. This comparative analysis provides insight into how photosynthetic systems are able to adapt and survive under challenging environmental conditions.

  2. Excited states in hydrocarbons

    SciTech Connect

    Lipsky, S.

    1987-01-01

    In this brief review we first summarize some pertinent features of the photophysical properties of excited states of hydrocarbons and the mechanisms by which they transfer energy to solutes and then review their yields and their behavior under fast-electron irradiation conditions. 33 refs.

  3. Ground Operations Demonstration Unit for Liquid Hydrogen (GODU LH2)

    NASA Technical Reports Server (NTRS)

    Notardonato, William U.

    2015-01-01

    When the technology associated with zero loss storage and transfer is implemented, NASA can reduce the LH2 losses and procurement costs by up to 30 compared to historical Shuttle numbers. This return on investment is based on the mission manifest and commodity use. LH2 densification can provide improved launch vehicle ascent performance by minimizing the size of the LH2 tanks or storing more mass of propellant in the given tank volume.

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

    NASA Astrophysics Data System (ADS)

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

    2004-01-01

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

  5. Distinguishing between keto-enol and acid-base forms of firefly oxyluciferin through calculation of excited-state equilibrium constants.

    PubMed

    Falklöf, Olle; Durbeej, Bo

    2014-11-15

    Although recent years have seen much progress in the elucidation of the mechanisms underlying the bioluminescence of fireflies, there is to date no consensus on the precise contributions to the light emission from the different possible forms of the chemiexcited oxyluciferin (OxyLH2) cofactor. Here, this problem is investigated by the calculation of excited-state equilibrium constants in aqueous solution for keto-enol and acid-base reactions connecting six neutral, monoanionic and dianionic forms of OxyLH2. Particularly, rather than relying on the standard Förster equation and the associated assumption that entropic effects are negligible, these equilibrium constants are for the first time calculated in terms of excited-state free energies of a Born-Haber cycle. Performing quantum chemical calculations with density functional theory methods and using a hybrid cluster-continuum approach to describe solvent effects, a suitable protocol for the modeling is first defined from benchmark calculations on phenol. Applying this protocol to the various OxyLH2 species and verifying that available experimental data (absorption shifts and ground-state equilibrium constants) are accurately reproduced, it is then found that the phenolate-keto-OxyLH(-) monoanion is intrinsically the preferred form of OxyLH2 in the excited state, which suggests a potential key role for this species in the bioluminescence of fireflies.

  6. Polaronic effects at finite temperatures in the B850 ring of the LH2 complex.

    PubMed

    Chorošajev, Vladimir; Rancova, Olga; Abramavicius, Darius

    2016-03-21

    Energy transfer and relaxation dynamics in the B850 ring of LH2 molecular aggregates are described, taking into account the polaronic effects, by a stochastic time-dependent variational approach. We explicitly include the finite temperature effects in the model by sampling the initial conditions of the vibrational states randomly. This is in contrast to previous applications of the variational approach, which consider only the zero-temperature case. The method allows us to obtain both the microscopic dynamics at the single-wavefunction level and the thermally averaged picture of excitation relaxation over a wide range of temperatures. Spectroscopic observables such as temperature dependent absorption and time-resolved fluorescence spectra are calculated. Microscopic wavefunction evolution is quantified by introducing the exciton participation (localization) length and the exciton coherence length. Their asymptotic temperature dependence demonstrates that the environmental polaronic effects range from exciton self-trapping and excitonic polaron formation at low temperatures to thermally induced state delocalization and decoherence at high temperatures. While the transition towards the polaronic state can be observed on the wavefunction level, it does not produce a discernible effect on the calculated spectroscopic observables.

  7. Cryogenic foam insulation for LH2 fueled subsonic transports

    NASA Technical Reports Server (NTRS)

    Sharpe, E. L.; Helenbrook, R. G.

    1978-01-01

    Shortages of petroleum-based aircraft fuels are foreseen before the end of the century. To cope with such shortages, NASA is developing a commercial aircraft which can operate on liquid hydrogen. Various foam insulators for LH2 storage are considered in terms of thermal performance and service life. Of the cryogenic foams considered (plain foam, foam with flame retardants and fiberglass reinforcement, and foam with vapor barriers), polyurethane foams were found to be the best. Tests consisted of heating a 5 cm layer of insulation around an aluminum tank containing LH2 to 316 K, and then cooling it to 266 K, while the inner surface was maintained at LH2 temperature (20 K).

  8. Measuring Thermal Conductivity at LH2 Temperatures

    NASA Technical Reports Server (NTRS)

    Selvidge, Shawn; Watwood, Michael C.

    2004-01-01

    For many years, the National Institute of Standards and Technology (NIST) produced reference materials for materials testing. One such reference material was intended for use with a guarded hot plate apparatus designed to meet the requirements of ASTM C177-97, "Standard Test Method for Steady-State Heat Flux Measurements and Thermal Transmission Properties by Means of the Guarded-Hot-Plate Apparatus." This apparatus can be used to test materials in various gaseous environments from atmospheric pressure to a vacuum. It allows the thermal transmission properties of insulating materials to be measured from just above ambient temperature down to temperatures below liquid hydrogen. However, NIST did not generate data below 77 K temperature for the reference material in question. This paper describes a test method used at NASA's Marshall Space Flight Center (MSFC) to optimize thermal conductivity measurements during the development of thermal protection systems. The test method extends the usability range of this reference material by generating data at temperatures lower than 77 K. Information provided by this test is discussed, as are the capabilities of the MSFC Hydrogen Test Facility, where advanced methods for materials testing are routinely developed and optimized in support of aerospace applications.

  9. Probing energy transfer events in the light harvesting complex 2 (LH2) of Rhodobacter sphaeroides with two-dimensional spectroscopy.

    PubMed

    Fidler, Andrew F; Singh, Ved P; Long, Phillip D; Dahlberg, Peter D; Engel, Gregory S

    2013-10-21

    Excitation energy transfer events in the photosynthetic light harvesting complex 2 (LH2) of Rhodobacter sphaeroides are investigated with polarization controlled two-dimensional electronic spectroscopy. A spectrally broadened pulse allows simultaneous measurement of the energy transfer within and between the two absorption bands at 800 nm and 850 nm. The phased all-parallel polarization two-dimensional spectra resolve the initial events of energy transfer by separating the intra-band and inter-band relaxation processes across the two-dimensional map. The internal dynamics of the 800 nm region of the spectra are resolved as a cross peak that grows in on an ultrafast time scale, reflecting energy transfer between higher lying excitations of the B850 chromophores into the B800 states. We utilize a polarization sequence designed to highlight the initial excited state dynamics which uncovers an ultrafast transfer component between the two bands that was not observed in the all-parallel polarization data. We attribute the ultrafast transfer component to energy transfer from higher energy exciton states to lower energy states of the strongly coupled B850 chromophores. Connecting the spectroscopic signature to the molecular structure, we reveal multiple relaxation pathways including a cyclic transfer of energy between the two rings of the complex.

  10. Cost Beneftt Analysts of LH2 PadB

    NASA Technical Reports Server (NTRS)

    Mott, Brittany

    2013-01-01

    This analysis is used to evaluate, from a cost and benefit perspective, potential outcomes when replacing the pressurization switches and the pressurization system to meet the needs of the LH2 storage system at Pad B. This also includes alternatives, tangible and intangible benefits, and the results of the analysis.

  11. Risk Assessment and Scaling for the SLS LH2 ET

    NASA Technical Reports Server (NTRS)

    Hafiychuk, Halyna; Ponizovskaya-Devine, Ekaterina; Luchinsky, Dmitry; Khasin, Michael; Osipov, Viatcheslav V.; Smelyanskiy, Vadim N.

    2012-01-01

    In this report the main physics processes in LH2 tank during prepress and rocket flight are studied. The goal of this investigation is to analyze possible hazards and to make risk assessment in proposed LH2 tank designs for SLS with 5 engines (the situation with 4 engines is less critical). For analysis we use the multinode model (MNM) developed by us and presented in a separate report and also 3D ANSYS simulations. We carry out simulation and theoretical analysis the physics processes such as (i) accumulation of bubbles in LH2 during replenish stage and their collapsing in the liquid during the prepress; (ii) condensation-evaporation at the liquid-vapor interface and tank wall, (iv) heating the liquid near the interface and wall due to condensation and environment heat, (v) injection of hot He during prepress and of hot GH2 during flight, (vi) mixing and cooling of the injected gases due to heat transfer between the gases, liquid and the tank wall. We analyze the effects of these physical processes on the thermo- and fluid gas dynamics in the ullage and on the stratification of temperature in the liquid and assess the associated hazards. A special emphasize is put on the scaling predictions for the larger SLS LH2 tank.

  12. Space-based LH 2 propellant storage system: subscale ground testing results

    NASA Astrophysics Data System (ADS)

    Liggett, M. W.

    An orbital cryogenic liquid storage facility will be one of the essential elements of the US Space Program to realize the benefits of space-based cryogenic propulsion vehicles such as NASA's space transfer vehicle (STV) for transporting personnel and scientific packages from a space station in low earth orbit (LEO) to geosynchronous orbit (GEO), the moon and beyond. Long-term thermal control of LH 2 and LO 2 storage cryotanks is a key technical objective for many NASA and SDI programmes. Improved retention using refrigeration, boil-off vapour-cooled shields (VCSs), multilayer superinsulation (MLI) and para-ortho (P-O) hydrogen conversion are the required state-of-the-art techniques. The cryotank system level development testing (CSLDT) programme has supported the development of these technologies. Under the programme, trade studies and analyses were followed by the design and construction of a subscale LH 2 storage facility test article for steady-state and transient thermal tests. A two-stage gaseous helium (GHe) refrigerator was integrated with the test article and used to reduce boil-off and/or decrease the time required between passive test configuration steady-state conditions. The LH 2 tank, mounted in a vacuum chamber, was thermally shielded from the chamber wall by MLI blankets and two VCSs. The VCSs were cooled with either LH 2 boil-off gas (through an optional P-O converter) or refrigerated GHe. The CSLDT test article design, assembly and results from 400 hours of thermal tests are presented along with important conclusions. A comparison of predicted and measured steady-state boil-off rates is provided for 10 test configurations, and the system time constant is addressed. Also presented are some of the unique issues and challenges encountered during these tests that are related to instrumentation and control.

  13. Atomistic modeling of two-dimensional electronic spectra and excited-state dynamics for a Light Harvesting 2 complex.

    PubMed

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

    2015-01-29

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

  14. Theoretical studies of electronically excited states

    SciTech Connect

    Besley, Nicholas A.

    2014-10-06

    Time-dependent density functional theory is the most widely used quantum chemical method for studying molecules in electronically excited states. However, excited states can also be computed within Kohn-Sham density functional theory by exploiting methods that converge the self-consistent field equations to give excited state solutions. The usefulness of single reference self-consistent field based approaches for studying excited states is demonstrated by considering the calculation of several types of spectroscopy including the infrared spectroscopy of molecules in an electronically excited state, the rovibrational spectrum of the NO-Ar complex, core electron binding energies and the emission spectroscopy of BODIPY in water.

  15. Resource Paper: Molecular Excited State Relaxation Processes.

    ERIC Educational Resources Information Center

    Rhodes, William

    1979-01-01

    Develops the concept of oscillatory v dissipative limits as it applies to electronic excited state processes in molecular systems. Main emphasis is placed on the radiative and nonradiative dynamics of the excited state of a molecule prepared by interaction with light or some other excitation source. (BT)

  16. Fracture Mechanics Analysis of LH2 Feed Line Flow Liners

    NASA Technical Reports Server (NTRS)

    James, Mark A.; Dawicke, David S.; Brzowski, Matthew B.; Raju, Ivatury S.; Elliott, Kenny B.; Harris, Charles E.

    2006-01-01

    Inspections of the Space Shuttle Main Engine revealed fatigue cracks growing from slots in the flow liner of the liquid hydrogen (LH2) feed lines. During flight, the flow liners experience complex loading induced by flow of LH2 and the resonance characteristics of the structure. The flow liners are made of Inconel 718 and had previously not been considered a fracture critical component. However, fatigue failure of a flow liner could have catastrophic effect on the Shuttle engines. A fracture mechanics study was performed to determine if a damage tolerance approach to life management was possible and to determine the sensitivity to the load spectra, material properties, and crack size. The load spectra were derived separately from ground tests and material properties were obtained from coupon tests. The stress-intensity factors for the fatigue cracks were determined from a shell-dynamics approach that simulated the dominant resonant frequencies. Life predictions were obtained using the NASGRO life prediction code. The results indicated that adequate life could not be demonstrated for initial crack lengths of the size that could be detected by traditional NDE techniques.

  17. Single-Molecule Spectroscopy Reveals that Individual Low-Light LH2 Complexes from Rhodopseudomonas palustris 2.1.6. Have a Heterogeneous Polypeptide Composition

    PubMed Central

    Brotosudarmo, Tatas H.P.; Kunz, Ralf; Böhm, Paul; Gardiner, Alastair T.; Moulisová, Vladimíra; Cogdell, Richard J.; Köhler, Jürgen

    2009-01-01

    Abstract Rhodopseudomonas palustris belongs to the group of purple bacteria that have the ability to produce LH2 complexes with unusual absorption spectra when they are grown at low-light intensity. This ability is often related to the presence of multiple genes encoding the antenna apoproteins. Here we report, for the first time to our knowledge, direct evidence that individual low-light LH2 complexes have a heterogeneous αβ-apoprotein composition that modulates the site energies of Bchl a molecules, producing absorption bands at 800, 820, and 850 nm. The arrangement of the Bchl a molecules in the “tightly coupled ring” can be modeled by nine αβ-Bchls dimers, such that the Bchls bound to six αβ-pairs have B820-like site energies and the remaining Bchl a molecules have B850-like site energies. Furthermore, the experimental data can only be satisfactorily modeled when these six αβ-pairs with B820 Bchl a molecules are distributed such that the symmetry of the assembly is reduced to C3. It is also clear from the measured single-molecule spectra that the energies of the electronically excited states in the mixed B820/850 ring are mainly influenced by diagonal disorder. PMID:19720038

  18. The Excited State Spectrum of QCD

    SciTech Connect

    Robert Edwards

    2010-08-01

    The determination of the highly excited state spectrum of baryons within QCD is a major theoretical and experimental challenge. I will present recent results from lattice QCD that give some indications on the structure of these highly excited states, and outline on-going and future work needed for a full determination of the spectrum, including strong decays.

  19. Doubly Excited States in Be III

    NASA Astrophysics Data System (ADS)

    Andersen, T.; Bentzen, S. M.; Poulsen, O.

    1980-01-01

    The triplet spectrum of doubly excited Be III has been studied in the wavelength region of 75-5000 Å in order to test the validity of the theoretical term values reported by Lipsky et al. The beam-foil excitation technique was applied to effectively populate the doubly excited states. The identified lower-lying, doubly excited states 2p2 3P, 2pnp 3P, or 3D, and 2pnd 3P, or 3D (n = 3, 4) show that the theoretical term values should be slightly modified.

  20. Slow excited state phototautomerization in 3-hydroxyisoquinoline.

    PubMed

    Joshi, Neeraj Kumar; Arora, Priyanka; Pant, Sanjay; Joshi, Hem Chandra

    2014-06-01

    In the present work we report the spectral and photophysical properties of 3-hydroxyisoquinoline in various protic/aprotic solvents. Our steady state and time resolved fluorescence data indicates that in the monomer form of 3HIQ phototautomerization can take place in the excited state through excited state intramolecular proton, while as per earlier suggestions phototautomerization in 3HIQ occurs in dimer or complex (in the presence of acetic acid) form. Moreover, we find rather slow tautomerization (occurring on the nanosecond scale). It is found that proton transfer occurs both in the ground as well as excited states and is controlled by the polarity of the solvent.

  1. Membrane Curvature Induced by Aggregates of LH2s and Monomeric LH1s

    PubMed Central

    Chandler, Danielle E.; Gumbart, James; Stack, John D.; Chipot, Christophe; Schulten, Klaus

    2009-01-01

    Abstract The photosynthetic apparatus of purple bacteria is contained within organelles called chromatophores, which form as extensions of the cytoplasmic membrane. The shape of these chromatophores can be spherical (as in Rhodobacter sphaeroides), lamellar (as in Rhodopseudomonas acidophila and Phaeospirillum molischianum), or tubular (as in certain Rb. sphaeroides mutants). Chromatophore shape is thought to be influenced by the integral membrane proteins Light Harvesting Complexes I and II (LH1 and LH2), which pack tightly together in the chromatophore. It has been suggested that the shape of LH2, together with its close packing in the membrane, induces membrane curvature. The mechanism of LH2-induced curvature is explored via molecular dynamics simulations of multiple LH2 complexes in a membrane patch. LH2s from three species—Rb. sphaeroides, Rps. acidophila, and Phsp. molischianum—were simulated in different packing arrangements. In each case, the LH2s pack together and tilt with respect to neighboring LH2s in a way that produces an overall curvature. This curvature appears to be driven by a combination of LH2's shape and electrostatic forces that are modulated by the presence of well-conserved cytoplasmic charged residues, the removal of which inhibits LH2 curvature. The interaction of LH2s and an LH1 monomer is also explored, and it suggests that curvature is diminished by the presence of LH1 monomers. The implications of our results for chromatophore shape are discussed. PMID:19948127

  2. Hydrogen Bonds in Excited State Proton Transfer

    NASA Astrophysics Data System (ADS)

    Horke, D. A.; Watts, H. M.; Smith, A. D.; Jager, E.; Springate, E.; Alexander, O.; Cacho, C.; Chapman, R. T.; Minns, R. S.

    2016-10-01

    Hydrogen bonding interactions between biological chromophores and their surrounding protein and solvent environment significantly affect the photochemical pathways of the chromophore and its biological function. A common first step in the dynamics of these systems is excited state proton transfer between the noncovalently bound molecules, which stabilizes the system against dissociation and principally alters relaxation pathways. Despite such fundamental importance, studying excited state proton transfer across a hydrogen bond has proven difficult, leaving uncertainties about the mechanism. Through time-resolved photoelectron imaging measurements, we demonstrate how the addition of a single hydrogen bond and the opening of an excited state proton transfer channel dramatically changes the outcome of a photochemical reaction, from rapid dissociation in the isolated chromophore to efficient stabilization and ground state recovery in the hydrogen bonded case, and uncover the mechanism of excited state proton transfer at a hydrogen bond, which follows sequential hydrogen and charge transfer processes.

  3. New Insights in 4f(12)5d(1) Excited States of Tm(2+) through Excited State Excitation Spectroscopy.

    PubMed

    de Jong, Mathijs; Biner, Daniel; Krämer, Karl W; Barandiarán, Zoila; Seijo, Luis; Meijerink, Andries

    2016-07-21

    Optical excitation of ions or molecules typically leads to an expansion of the equilibrium bond lengths in the excited electronic state. However, for 4f(n-1)5d(1) excited states in lanthanide ions both expansion and contraction relative to the 4f(n) ground state have been reported, depending on the crystal field and nature of the 5d state. To probe the equilibrium distance offset between different 4f(n-1)5d(1) excited states, we report excited state excitation (ESE) spectra for Tm(2+) doped in CsCaBr3 and CsCaCl3 using two-color excited state excitation spectroscopy. The ESE spectra reveal sharp lines at low energies, confirming a similar distance offset for 4f(n-1)5d(t2g)(1) states. At higher energies, broader bands are observed, which indicate the presence of excited states with a different offset. On the basis of ab initio embedded-cluster calculations, the broad bands are assigned to two-photon d-d absorption from the excited state. In this work, we demonstrate that ESE is a powerful spectroscopic tool, giving access to information which cannot be obtained through regular one-photon spectroscopy. PMID:27347766

  4. New Insights in 4f(12)5d(1) Excited States of Tm(2+) through Excited State Excitation Spectroscopy.

    PubMed

    de Jong, Mathijs; Biner, Daniel; Krämer, Karl W; Barandiarán, Zoila; Seijo, Luis; Meijerink, Andries

    2016-07-21

    Optical excitation of ions or molecules typically leads to an expansion of the equilibrium bond lengths in the excited electronic state. However, for 4f(n-1)5d(1) excited states in lanthanide ions both expansion and contraction relative to the 4f(n) ground state have been reported, depending on the crystal field and nature of the 5d state. To probe the equilibrium distance offset between different 4f(n-1)5d(1) excited states, we report excited state excitation (ESE) spectra for Tm(2+) doped in CsCaBr3 and CsCaCl3 using two-color excited state excitation spectroscopy. The ESE spectra reveal sharp lines at low energies, confirming a similar distance offset for 4f(n-1)5d(t2g)(1) states. At higher energies, broader bands are observed, which indicate the presence of excited states with a different offset. On the basis of ab initio embedded-cluster calculations, the broad bands are assigned to two-photon d-d absorption from the excited state. In this work, we demonstrate that ESE is a powerful spectroscopic tool, giving access to information which cannot be obtained through regular one-photon spectroscopy.

  5. Hybrid Composites for LH2 Fuel Tank Structure

    NASA Technical Reports Server (NTRS)

    Grimsley, Brian W.; Cano, Roberto J.; Johnston, Norman J.; Loos, Alfred C.; McMahon, William M.

    2001-01-01

    The application of lightweight carbon fiber reinforced plastics (CFRP) as structure for cryogenic fuel tanks is critical to the success of the next generation of Reusable Launch Vehicles (RLV). The recent failure of the X-33 composite fuel tank occurred in part due to microcracking of the polymer matrix, which allowed cryogen to permeate through the inner skin to the honeycomb core. As part of an approach to solve these problems, NASA Langley Research Center (LaRC) and Marshall Space Flight Center (MSFC) are working to develop and investigate polymer films that will act as a barrier to the permeation of LH2 through the composite laminate. In this study two commercially available films and eleven novel LaRC films were tested in an existing cryogenics laboratory at MSFC to determine the permeance of argon at room temperature. Several of these films were introduced as a layer in the composite to form an interleaved, or hybrid, composite to determine the effects on permeability. In addition, the effects of the interleaved layer thickness, number, and location on the mechanical properties of the composite laminate were investigated. In this initial screening process, several of the films were found to exhibit lower permeability to argon than the composite panels tested.

  6. Close-in characteristics of LH2/LOX reactions

    NASA Technical Reports Server (NTRS)

    Riehl, W. A.; Ullian, L. J.

    1985-01-01

    In deriving shock overpressures from space vehicles employing LH2 and LOX, separate methods of analyses and prediction are recommended, as a function of the distance. Three methods of treatment are recommended. For the Far Field - where the expected shock overpressure is less than 40 psi (lambda = 5) - use the classical PYRO approach to determine TNT yield, and employ classical ordnance (Kingery) curve to obtain the overall value. For the Close-In Range, a suggested limit is 3D, or a zone from a distance of three times the tank diameter to the tank wall. Rather than estimate a specific distance from the center of explosion to the target, it is only necessary to estimate whether this could be within one, two, or three diameters away from the wall; i.e., in the 1, 2, or 3D zone. Then assess whether mixing mode is by the PYRO CBGS (spill) mode or CBM (internal mixing) mode. From the zone and mixing mode, the probability of attaining various shock overpressures is determined from the plots provided herein. For the transition zone, between 40 psi and the 3D distance, it is tentatively recommended that both of the preceding methods be used, and to be conservative, the higher resulting value be used.

  7. Characterisation of the LH2 spectral variants produced by the photosynthetic purple sulphur bacterium Allochromatium vinosum.

    PubMed

    Carey, Anne-Marie; Hacking, Kirsty; Picken, Nichola; Honkanen, Suvi; Kelly, Sharon; Niedzwiedzki, Dariusz M; Blankenship, Robert E; Shimizu, Yuuki; Wang-Otomo, Zheng-Yu; Cogdell, Richard J

    2014-11-01

    This study systematically investigated the different types of LH2 produced by Allochromatium (Alc.) vinosum, a photosynthetic purple sulphur bacterium, in response to variations in growth conditions. Three different spectral forms of LH2 were isolated and purified, the B800-820, B800-840 and B800-850 LH2 types, all of which exhibit an unusual split 800 peak in their low temperature absorption spectra. However, it is likely that more forms are also present. Relatively more B800-820 and B800-840 are produced under low light conditions, while relatively more B800-850 is produced under high light conditions. Polypeptide compositions of the three different LH2 types were determined by a combination of HPLC and TOF/MS. The B800-820, B800-840 and B800-850 LH2 types all have a heterogeneous polypeptide composition, containing multiple types of both α and β polypeptides, and differ in their precise polypeptide composition. They all have a mixed carotenoid composition, containing carotenoids of the spirilloxanthin series. In all cases the most abundant carotenoid is rhodopin; however, there is a shift towards carotenoids with a higher conjugation number in LH2 complexes produced under low light conditions. CD spectroscopy, together with the polypeptide analysis, demonstrates that these Alc. vinosum LH2 complexes are more closely related to the LH2 complex from Phs. molischianum than they are to the LH2 complexes from Rps. acidophila. PMID:25111749

  8. Characterisation of the LH2 spectral variants produced by the photosynthetic purple sulphur bacterium Allochromatium vinosum.

    PubMed

    Carey, Anne-Marie; Hacking, Kirsty; Picken, Nichola; Honkanen, Suvi; Kelly, Sharon; Niedzwiedzki, Dariusz M; Blankenship, Robert E; Shimizu, Yuuki; Wang-Otomo, Zheng-Yu; Cogdell, Richard J

    2014-11-01

    This study systematically investigated the different types of LH2 produced by Allochromatium (Alc.) vinosum, a photosynthetic purple sulphur bacterium, in response to variations in growth conditions. Three different spectral forms of LH2 were isolated and purified, the B800-820, B800-840 and B800-850 LH2 types, all of which exhibit an unusual split 800 peak in their low temperature absorption spectra. However, it is likely that more forms are also present. Relatively more B800-820 and B800-840 are produced under low light conditions, while relatively more B800-850 is produced under high light conditions. Polypeptide compositions of the three different LH2 types were determined by a combination of HPLC and TOF/MS. The B800-820, B800-840 and B800-850 LH2 types all have a heterogeneous polypeptide composition, containing multiple types of both α and β polypeptides, and differ in their precise polypeptide composition. They all have a mixed carotenoid composition, containing carotenoids of the spirilloxanthin series. In all cases the most abundant carotenoid is rhodopin; however, there is a shift towards carotenoids with a higher conjugation number in LH2 complexes produced under low light conditions. CD spectroscopy, together with the polypeptide analysis, demonstrates that these Alc. vinosum LH2 complexes are more closely related to the LH2 complex from Phs. molischianum than they are to the LH2 complexes from Rps. acidophila.

  9. Charmonium excited state spectrum in lattice QCD

    SciTech Connect

    Jozef Dudek; Robert Edwards; Nilmani Mathur; David Richards

    2008-02-01

    Working with a large basis of covariant derivative-based meson interpolating fields we demonstrate the feasibility of reliably extracting multiple excited states using a variational method. The study is performed on quenched anisotropic lattices with clover quarks at the charm mass. We demonstrate how a knowledge of the continuum limit of a lattice interpolating field can give additional spin-assignment information, even at a single lattice spacing, via the overlap factors of interpolating field and state. Excited state masses are systematically high with respect to quark potential model predictions and, where they exist, experimental states. We conclude that this is most likely a result of the quenched approximation.

  10. Impact of ground- and excited-state aromaticity on cyclopentadiene and silole excitation energies and excited-state polarities.

    PubMed

    Jorner, Kjell; Emanuelsson, Rikard; Dahlstrand, Christian; Tong, Hui; Denisova, Aleksandra V; Ottosson, Henrik

    2014-07-21

    A new qualitative model for estimating the properties of substituted cyclopentadienes and siloles in their lowest ππ* excited states is introduced and confirmed through quantum chemical calculations, and then applied to explain earlier reported experimental excitation energies. According to our model, which is based on excited-state aromaticity and antiaromaticity, siloles and cyclopentadienes are cross-hyperconjugated "aromatic chameleons" that adapt their electronic structures to conform to the various aromaticity rules in different electronic states (Hückel's rule in the π(2) electronic ground state (S0) and Baird's rule in the lowest ππ* excited singlet and triplet states (S1 and T1)). By using pen-and-paper arguments, one can explain polarity changes upon excitation of substituted cyclopentadienes and siloles, and one can tune their lowest excitation energies by combined considerations of ground- and excited-state aromaticity/antiaromaticity effects. Finally, the "aromatic chameleon" model can be extended to other monocyclic compound classes of potential use in organic electronics, thereby providing a unified view of the S0, T1, and S1 states of a range of different cyclic cross-π-conjugated and cross-hyperconjugated compound classes. PMID:25043523

  11. Excited intruder states in {sup 32}Mg

    SciTech Connect

    Tripathi, Vandana; Tabor, S. L.; Bender, P.; Hoffman, C. R.; Lee, Sangjin; Pepper, K.; Perry, M.; Utsuno, Y.; Otsuka, T.; Mantica, P. F.; Pinter, J. S.; Stoker, J. B.; Cook, J. M.; Pereira, J.; Weisshaar, D.

    2008-03-15

    The low energy level structure of N=20 {sup 32}Mg obtained via {beta}-delayed {gamma} spectroscopy is reported. The level structure of {sup 32}Mg is found to be completely dominated by intruders. An inversion between the 1p-1h and 3p-3h states is observed for the negative parity states, similar to the 0p-0h and 2p-2h inversion for the positive parity states in these N{approx}20 nuclei. The intruder excited states, both positive and negative parity, are reasonably explained by Monte Carlo shell model calculations, which suggest a shrinking N=20 shell gap with decreasing Z.

  12. Paramagnetic excited vortex states in superconductors

    NASA Astrophysics Data System (ADS)

    Gomes, Rodolpho Ribeiro; Doria, Mauro M.; Romaguera, Antonio R. de C.

    2016-06-01

    We consider excited vortex states, which are vortex states left inside a superconductor once the external applied magnetic field is switched off and whose energy is lower than of the normal state. We show that this state is paramagnetic and develop here a general method to obtain its Gibbs free energy through conformal mapping. The solution for any number of vortices in any cross-section geometry can be read off from the Schwarz-Christoffel mapping. The method is based on the first-order equations used by Abrikosov to discover vortices.

  13. STIRAP on helium: Excitation to Rydberg states

    NASA Astrophysics Data System (ADS)

    Yuan, Deqian

    Research in optically induced transitions between dierent atomic levels has a long history. For transitions between states driven by a coherent optical eld, the theoretical eciency could be ideally high as 100% but there could be many factors preventing this. In the three state helium atom excitation process, i.e. 23S→33P→nL , the stimulated emission from intermediate state makes it hard to achieve ecient population transfer to the nal state through an intuitive excitation order. One technique to achieve a higher eciency is Stimulated Raman Adiabatic Passage (STIRAP) which is being studied and under research in our lab. Unlike traditional three level excitation processes, STIRAP actually uses a counter intuitive pulsed laser beams timing arrangement. The excitation objects are metastable helium atoms traveling in a vacuum system with a longitudinal velocity of ~ 1070 m/s. We are using a 389 nm UV laser to connect the 23S and the 33P state and a frequency tunable ~790 nm IR laser to connect the 33P state and the dierent Rydberg states. A third 1083 nm wavelength laser beam drives the 23S → 23P transition to transversely separate the residual metastable atoms and the Rydberg atoms for eciency measurements. The data is taken by a stainless steel detector in the vacuum system. As the Rydberg atoms will get ionized by blackbody radiation under room temperature, we can utilize this for their detection. An ion detector sitting on the eld plate is capable to collect the ion signals of the Rydberg atoms for detection. So far the whole system has not been ready for data collection and measurement, so here we are using data and results from previous theses for discussions. The highest transition frequency that has ever been achieved in our lab is around 70% after corrections.

  14. Accelerating slow excited state proton transfer.

    PubMed

    Stewart, David J; Concepcion, Javier J; Brennaman, M Kyle; Binstead, Robert A; Meyer, Thomas J

    2013-01-15

    Visible light excitation of the ligand-bridged assembly [(bpy)(2)Ru(a)(II)(L)Ru(b)(II)(bpy)(OH(2))(4+)] (bpy is 2,2'-bipyridine; L is the bridging ligand, 4-phen-tpy) results in emission from the lowest energy, bridge-based metal-to-ligand charge transfer excited state (L(-•))Ru(b)(III)-OH(2) with an excited-state lifetime of 13 ± 1 ns. Near-diffusion-controlled quenching of the emission occurs with added HPO(4)(2-) and partial quenching by added acetate anion (OAc(-)) in buffered solutions with pH control. A Stern-Volmer analysis of quenching by OAc(-) gave a quenching rate constant of k(q) = 4.1 × 10(8) M(-1) • s(-1) and an estimated pK(a)* value of ~5 ± 1 for the [(bpy)(2)Ru(a)(II)(L(•-))Ru(b)(III)(bpy)(OH(2))(4+)]* excited state. Following proton loss and rapid excited-state decay to give [(bpy)(2)Ru(a)(II)(L)Ru(b)(II)(bpy)(OH)(3+)] in a H(2)PO(4)(-)/HPO(4)(2-) buffer, back proton transfer occurs from H(2)PO(4)(-) to give [(bpy)(2)Ru(a)(II)(L)Ru(b)(bpy)(OH(2))(4+)] with k(PT,2) = 4.4 × 10(8) M(-1) • s(-1). From the intercept of a plot of k(obs) vs. [H(2)PO(4)(-)], k = 2.1 × 10(6) s(-1) for reprotonation by water providing a dramatic illustration of kinetically limiting, slow proton transfer for acids and bases with pK(a) values intermediate between pK(a)(H(3)O(+)) = -1.74 and pK(a)(H(2)O) = 15.7. PMID:23277551

  15. Accelerating slow excited state proton transfer

    PubMed Central

    Stewart, David J.; Concepcion, Javier J.; Brennaman, M. Kyle; Binstead, Robert A.; Meyer, Thomas J.

    2013-01-01

    Visible light excitation of the ligand-bridged assembly [(bpy)2RuaII(L)RubII(bpy)(OH2)4+] (bpy is 2,2′-bipyridine; L is the bridging ligand, 4-phen-tpy) results in emission from the lowest energy, bridge-based metal-to-ligand charge transfer excited state (L−•)RubIII-OH2 with an excited-state lifetime of 13 ± 1 ns. Near–diffusion-controlled quenching of the emission occurs with added HPO42− and partial quenching by added acetate anion (OAc−) in buffered solutions with pH control. A Stern–Volmer analysis of quenching by OAc− gave a quenching rate constant of kq = 4.1 × 108 M−1⋅s−1 and an estimated pKa* value of ∼5 ± 1 for the [(bpy)2RuaII(L•−)RubIII(bpy)(OH2)4+]* excited state. Following proton loss and rapid excited-state decay to give [(bpy)2RuaII(L)RubII(bpy)(OH)3+] in a H2PO4−/HPO42− buffer, back proton transfer occurs from H2PO4− to give [(bpy)2RuaII(L)Rub(bpy)(OH2)4+] with kPT,2 = 4.4 × 108 M−1⋅s−1. From the intercept of a plot of kobs vs. [H2PO4−], k = 2.1 × 106 s−1 for reprotonation by water providing a dramatic illustration of kinetically limiting, slow proton transfer for acids and bases with pKa values intermediate between pKa(H3O+) = −1.74 and pKa(H2O) = 15.7. PMID:23277551

  16. CHARMONIUM EXCITED STATES FROM LATTICE QCD

    SciTech Connect

    Jozef Dudek; Robert Edwards; Nilmani Mathur; David Richards

    2007-11-20

    We apply the variational method with a large basis of interpolating operators to demonstrate the feasibility of extracting multiple excited states in charmonium from lattice QCD. The calculation is performed in the quenched approximation to QCD, using the clover fermion action on an anisotropic lattice. A crucial element of our approach is a knowledge of the continuum limit of the interpolating operators, providing important additional information on the spin assignment of the states, even at a single value of the lattice spacing. Though we find excited-state masses that are systematically high with respect to the quark potential model, and the experimental masses where known, we attribute this as most likely an artifact of the quenched approximation.

  17. Photoionization from excited states of helium

    NASA Technical Reports Server (NTRS)

    Jacobs, V. L.

    1973-01-01

    The cross sections for photoionization from the 2 1S, 2 3S, 2 1P and 2 3P excited states of helium are calculated for photoelectron energies below the n = 2 threshold of He(+) using Hylleraas bound state wave functions and 1s-2s-2p close coupling final state wave functions. The resonant structures associated with the lowest-lying 1S, 1P, 3P, and 1D autoionizing states of helium are found to be characterized by large values of the line profile parameter q. The cross sections and the photoelectron angular distribution asymmetry parameters for the P-states are calculated for various polarization states of the target atom and the incident photon. Experiments which would lead to the separate determinations of the S- and D- wave partial photoionization cross sections are discussed.

  18. Relaxation dynamics of the LH2 complex from a photosynthetic purple bacterium Thiorhodospira sibirica studied by the near-IR femtosecond pump-probe method

    SciTech Connect

    Razjivin, A P; Pishchal'nikov, R Yu; Kozlovskii, V S; Kompanets, V O; Chekalin, Sergei V; Moskalenko, A A; Makhneva, Z K

    2005-01-31

    Photoinduced changes in the absorption spectrum of the LH2 (B800-830-850) complex from a Thiorhodospira sibirica (Trs. sibirica) bacterium are studied by the pump-probe method. The complex has the anomalous absorption spectrum exhibiting three bands in the near-IR region at 793, 826.5, and 846.5 nm. At room temperature, the excitation energy transfer from the B800, B830, and B859 bands was detected with the time constants {tau}{sub 1{approx}}0.5 ps, {tau}{sub 2{approx}}2.5 ps, and {tau}{sub 3} of the order of a few hundreds of picoseconds, respectively. A rapid energy transfer from the B830 band compared to energy transfer from the B850 band ({tau}{sub 2}||{tau}{sub 3}) suggests that all the three bands belong to the same complex (i.e., that the LH2 complex from Trs. sibirica is homogeneous). A slower energy transfer (by three - five times) from the B830 band of the LH2 complex from Trs. sibirica compared to energy transfer from the B800 band of the LH2 complexes (B800-850 and especially B800-820) from other purple bacteria suggests that the electronic structures of ensembles of bacteriochlorophyll molecules in these complexes are substantially different. (laser applications and other topics in quantum electronics)

  19. Excited state baryon spectroscopy from lattice QCD

    DOE PAGES

    Robert G. Edwards; Dudek, Jozef J.; Richards, David G.; Wallace, Stephen J.

    2011-10-31

    Here, we present a calculation of the Nucleon and Delta excited state spectrum on dynamical anisotropic clover lattices. A method for operator construction is introduced that allows for the reliable identification of the continuum spins of baryon states, overcoming the reduced symmetry of the cubic lattice. Using this method, we are able to determine a spectrum of single-particle states for spins up to and including $J = 7/2$, of both parities, the first time this has been achieved in a lattice calculation. We find a spectrum of states identifiable as admixtures of $SU(6) Ⓧ O(3)$ representations and a counting ofmore » levels that is consistent with the non-relativistic $qqq$ constituent quark model. This dense spectrum is incompatible with quark-diquark model solutions to the "missing resonance problem" and shows no signs of parity doubling of states.« less

  20. Excited state baryon spectroscopy from lattice QCD

    SciTech Connect

    Edwards, Robert G.; Richards, David G.; Dudek, Jozef J.; Wallace, Stephen J.

    2011-10-01

    We present a calculation of the Nucleon and Delta excited state spectra on dynamical anisotropic clover lattices. A method for operator construction is introduced that allows for the reliable identification of the continuum spins of baryon states, overcoming the reduced symmetry of the cubic lattice. Using this method, we are able to determine a spectrum of single-particle states for spins up to and including J=(7/2), of both parities, the first time this has been achieved in a lattice calculation. We find a spectrum of states identifiable as admixtures of SU(6) x O(3) representations and a counting of levels that is consistent with the nonrelativistic qqq constituent quark model. This dense spectrum is incompatible with quark-diquark model solutions to the 'missing resonance problem' and shows no signs of parity doubling of states.

  1. Excited state baryon spectroscopy from lattice QCD

    SciTech Connect

    Robert G. Edwards; Dudek, Jozef J.; Richards, David G.; Wallace, Stephen J.

    2011-10-31

    Here, we present a calculation of the Nucleon and Delta excited state spectrum on dynamical anisotropic clover lattices. A method for operator construction is introduced that allows for the reliable identification of the continuum spins of baryon states, overcoming the reduced symmetry of the cubic lattice. Using this method, we are able to determine a spectrum of single-particle states for spins up to and including $J = 7/2$, of both parities, the first time this has been achieved in a lattice calculation. We find a spectrum of states identifiable as admixtures of $SU(6) Ⓧ O(3)$ representations and a counting of levels that is consistent with the non-relativistic $qqq$ constituent quark model. This dense spectrum is incompatible with quark-diquark model solutions to the "missing resonance problem" and shows no signs of parity doubling of states.

  2. Excited States of {sup 11}Be

    SciTech Connect

    Cappuzzello, F.; Cunsolo, A.; Fortier, S.; Foti, A.; Laurent, H.; Lenske, H.; Maison, J.M.; Melita, A.L.; Nociforo, C.; Rosier, L.; Stephan, C.; Tassan-Got, L.; Winfield, J.S.; Wolter, H.H.

    2000-12-31

    The {sup 11}B({sup 7}Li,{sup 7}Be){sup 11}Be reaction at 57 MeV incident energy was used to explore the {sup 11}Be excitation energy spectrum at forward angles. Angular distributions were extracted for the transitions to the ground and to the states of {sup 11}Be at excitation energies of E*=0.32, 1.78, 2.69, 3.41, 3.89, 3.96, 6.05 MeV combined with the ground and the first excited state of {sup 7}Be. Also the SDR [1][2] oscillation mode was observed at E*=9.5 MeV and FWHM{approx}9 MeV and a new peak at E*=6.05 MeV and FWHM{approx}0.3 MeV was observed. QRPA calculations in the G-matrix representation are in progress in order to describe the continuum structure of {sup 11}Be. DWBA calculations have been started to evaluate transferred angular momenta both in the one step and in the two steps dynamical framework.

  3. Ensemble density functional theory method correctly describes bond dissociation, excited state electron transfer, and double excitations

    SciTech Connect

    Filatov, Michael; Huix-Rotllant, Miquel; Burghardt, Irene

    2015-05-14

    State-averaged (SA) variants of the spin-restricted ensemble-referenced Kohn-Sham (REKS) method, SA-REKS and state-interaction (SI)-SA-REKS, implement ensemble density functional theory for variationally obtaining excitation energies of molecular systems. In this work, the currently existing version of the SA-REKS method, which included only one excited state into the ensemble averaging, is extended by adding more excited states to the averaged energy functional. A general strategy for extension of the REKS-type methods to larger ensembles of ground and excited states is outlined and implemented in extended versions of the SA-REKS and SI-SA-REKS methods. The newly developed methods are tested in the calculation of several excited states of ground-state multi-reference systems, such as dissociating hydrogen molecule, and excited states of donor–acceptor molecular systems. For hydrogen molecule, the new method correctly reproduces the distance dependence of the lowest excited state energies and describes an avoided crossing between the doubly excited and singly excited states. For bithiophene–perylenediimide stacked complex, the SI-SA-REKS method correctly describes crossing between the locally excited state and the charge transfer excited state and yields vertical excitation energies in good agreement with the ab initio wavefunction methods.

  4. Ensemble density functional theory method correctly describes bond dissociation, excited state electron transfer, and double excitations.

    PubMed

    Filatov, Michael; Huix-Rotllant, Miquel; Burghardt, Irene

    2015-05-14

    State-averaged (SA) variants of the spin-restricted ensemble-referenced Kohn-Sham (REKS) method, SA-REKS and state-interaction (SI)-SA-REKS, implement ensemble density functional theory for variationally obtaining excitation energies of molecular systems. In this work, the currently existing version of the SA-REKS method, which included only one excited state into the ensemble averaging, is extended by adding more excited states to the averaged energy functional. A general strategy for extension of the REKS-type methods to larger ensembles of ground and excited states is outlined and implemented in extended versions of the SA-REKS and SI-SA-REKS methods. The newly developed methods are tested in the calculation of several excited states of ground-state multi-reference systems, such as dissociating hydrogen molecule, and excited states of donor-acceptor molecular systems. For hydrogen molecule, the new method correctly reproduces the distance dependence of the lowest excited state energies and describes an avoided crossing between the doubly excited and singly excited states. For bithiophene-perylenediimide stacked complex, the SI-SA-REKS method correctly describes crossing between the locally excited state and the charge transfer excited state and yields vertical excitation energies in good agreement with the ab initio wavefunction methods.

  5. The role of betaArg-10 in the B800 bacteriochlorophyll and carotenoid pigment environment within the light-harvesting LH2 complex of Rhodobacter sphaeroides.

    PubMed

    Fowler, G J; Hess, S; Pullerits, T; Sundström, V; Hunter, C N

    1997-09-16

    within LH2. Similarly, carotenoid to bacteriochlorophyll energy transfer was largely unaffected, although shifts in the excitation spectra in the carotenoid region were noted. These betaArg-10 mutant complexes provide an opportunity to investigate the structural requirements for the binding of monomeric bacteriochlorophyll and to examine the basis of the red shift seen for bacteriochlorophyll in photosynthetic complexes, in addition to providing new information about the environment of the carotenoid pigments in this complex. PMID:9287171

  6. The role of betaArg-10 in the B800 bacteriochlorophyll and carotenoid pigment environment within the light-harvesting LH2 complex of Rhodobacter sphaeroides.

    PubMed

    Fowler, G J; Hess, S; Pullerits, T; Sundström, V; Hunter, C N

    1997-09-16

    within LH2. Similarly, carotenoid to bacteriochlorophyll energy transfer was largely unaffected, although shifts in the excitation spectra in the carotenoid region were noted. These betaArg-10 mutant complexes provide an opportunity to investigate the structural requirements for the binding of monomeric bacteriochlorophyll and to examine the basis of the red shift seen for bacteriochlorophyll in photosynthetic complexes, in addition to providing new information about the environment of the carotenoid pigments in this complex.

  7. Doubly excited states in some light atoms

    SciTech Connect

    Berry, H.G.; Brooks, R.L.; Hardis, J.E.; Ray, W.J.

    1981-01-01

    We have identified a singlet transition in doubly excited helium: 2p/sup 2/ /sup 1/D - 2p3d /sup 1/D, at 3298 +- 2A with a full width of 54A or 0.061 +- 0.005 eV. This width is in good agreement with a previous measurement and theory for the width of the 2p/sup 2/ /sup 1/D/sub 2/ state. We have remeasured the decay rate of 1s/sup 2/2p/sup 2/P - 1s2p/sup 2/ /sup 2/P in Li I and find it is in good agreement with theory. Several transitions in doubly excited Li II have been identified in the 1000A region. No evidence was found for doubly excited quartet transitions in Li I in the vacuum ultraviolet. We present measurements of wavelengths and fine structure of the 1s2s2p/sup 2/ /sup 5/P - 1s2p/sup 3/ /sup 5/S transitions in C III, N IV and O V.

  8. High-resolution AFM topographs of Rubrivivax gelatinosus light-harvesting complex LH2

    PubMed Central

    Scheuring, Simon; Reiss-Husson, Francoise; Engel, Andreas; Rigaud, Jean-Louis; Ranck, Jean-Luc

    2001-01-01

    Light-harvesting complexes 2 (LH2) are the accessory antenna proteins in the bacterial photosynthetic apparatus and are built up of αβ-heterodimers containing three bacteriochlorophylls and one carotenoid each. We have used atomic force microscopy (AFM) to investigate reconstituted LH2 from Rubrivivax gelatinosus, which has a C-terminal hydrophobic extension of 21 amino acids on the α-subunit. High-resolution topographs revealed a nonameric organization of the regularly packed cylindrical complexes incorporated into the membrane in both orientations. Native LH2 showed one surface which protruded by ∼6 Å and one that protruded by ∼14 Å from the membrane. Topographs of samples reconstituted with thermolysin-digested LH2 revealed a height reduction of the strongly protruding surface to ∼9 Å, and a change of its surface appearance. These results suggested that the α-subunit of R.gelatinosus comprises a single transmembrane helix and an extrinsic C-terminus, and allowed the periplasmic surface to be assigned. Occasionally, large rings (∼120 Å diameter) surrounded by LH2 rings were observed. Their diameter and appearance suggest the large rings to be LH1 complexes. PMID:11406579

  9. Lifetime of the Excited State In Vivo

    PubMed Central

    Govindjee; Hammond, J. H.; Merkelo, H.

    1972-01-01

    Lifetime of the excited state (τ) of bacteriochlorophyll (BChl) in photosynthetic bacteria, measured with a mode-locked argon laser (oscillating at 488 nm; mode locked at 56 MHz) as light source, ranged from 0.3 to 2.5 nsec. These τ values are reported with a precision of ±0.1 nsec. The value of τ at high exciting light intensity (I) was two to three times that at low intensity. For young cultures of green bacterium Chloropseudomonas ethylicum, τ ranged from 0.5 (low I) to 1.0 nsec (high I); for those of the purple bacterium Rhodospirillum rubrum, from 0.4 (low I) to 1.0 nsec (high I); and for those of the BChl b-containing Rhodopseudomonas viridis, from 1.0 (low I) to 2.5 nsec (high I). These data provide information regarding the efficiencies of the photochemical process in these bacteria. Quantum yield (ø) of BChl fluorescence, calculated from ø = τ/τ0 (where τ0 is the intrinsic lifetime of fluorescence), ranges from 2-6% at low intensities to 6-14% at high intensities. PMID:4624833

  10. Excited State Properties of Hybrid Perovskites.

    PubMed

    Saba, Michele; Quochi, Francesco; Mura, Andrea; Bongiovanni, Giovanni

    2016-01-19

    Metal halide perovskites have come to the attention of the scientific community for the progress achieved in solar light conversion. Energy sustainability is one of the priorities of our society, and materials advancements resulting in low-cost but efficient solar cells and large-area lighting devices represent a major goal for applied research. From a basic point of view, perovskites are an exotic class of hybrid materials combining some merits of organic and inorganic semiconductors: large optical absorption, large mobilities, and tunable band gap together with the possibility to be processed in solution. When a novel class of promising semiconductors comes into the limelight, lively discussions ensue on the photophysics of band-edge excitations, because just the states close to the band edge are entailed in energy/charge transport and light emission. This was the case several decades ago for III-V semiconductors, it has been up to 10 years ago for organics, and it is currently the case for perovskites. Our aim in this Account is to rationalize the body of experimental evidence on perovskite photophysics in a coherent theoretical framework, borrowing from the knowledge acquired over the years in materials optoelectronics. A crucial question is whether photon absorption leads to a population of unbound, conductive free charges or instead excitons, neutral and insulating bound states created by Coulomb interaction just below the energy of the band gap. We first focus on the experimental estimates of the exciton binding energy (Eb): at room temperature, Eb is comparable to the thermal energy kBT in MAPbI3 and increases up to values 2-3kBT in wide band gap MAPbBr3 and MAPbCl3. Statistical considerations predict that these values, even though comparable to or larger than thermal energy, let free carriers prevail over bound excitons for all levels of excitation densities relevant for devices. The analysis of photophysics evidence confirms that all hybrid halide

  11. Standoff alpha radiation detection via excited state absorption of air

    SciTech Connect

    Yao, Jimmy; Yin, Stuart Shizhuo; Brenizer, Jack; Hui, Rongqing

    2013-06-24

    A standoff alpha radiation detection technique based on the physical mechanism of excited state absorption of air molecules was explored and is presented in this paper. Instead of directly detecting the radiation via measuring the intensity of radiation induced air fluorescence, the radiation is detected via the excited state absorption of alpha radiation excited/ionized air molecules. Both theoretical analyses and experimental verifications were conducted. The experimental results confirmed that the radiation could be detected via excited state absorption of radiation excited/ionized air molecules at a 10 m standoff distance, which was consistent with the theoretical analyses.

  12. Transient simulation of LOX/LH2 rocket engine, LE-7

    NASA Astrophysics Data System (ADS)

    Kanmuri, Akio; Wakamatsu, Yoshio; Kanda, Takeshi; Torii, Yoshihiro; Nagao, Ryuuji; Kitakura, Kazuhisa; Okada, Masashi; Imoto, Takayuki; Saito, Takashi; Hasegawa, Keiichi

    A start transient simulation calculation program was developed for the LE-7 LOX/LH2 rocket engine based on the quasi-steady model. Comparisons between simulation and test results are reported which show that simulation improvements and engine parameter adjustments are required. A brief description of the engine system is given.

  13. Properties of chrysene in the higher triplet excited state

    NASA Astrophysics Data System (ADS)

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

    2003-01-01

    Properties of chrysene in the higher triplet excited state were studied by the two-color two-laser flash photolysis method. Triplet energy transfers from chrysene in the higher triplet excited state to quenchers such as biphenyl and naphthalene, and from the quenchers in the triplet excited state back to chrysene in the ground state were observed to proceed at the diffusion-controlled rate. From dependence of the quenching efficiency on the quencher concentration, the lifetime of chrysene in the higher triplet excited state was estimated to be 60 ps with considering the time-dependent quenching.

  14. Excited state quantum phase transitions in many-body systems

    SciTech Connect

    Caprio, M.A. Cejnar, P.; Iachello, F.

    2008-05-15

    Phenomena analogous to ground state quantum phase transitions have recently been noted to occur among states throughout the excitation spectra of certain many-body models. These excited state phase transitions are manifested as simultaneous singularities in the eigenvalue spectrum (including the gap or level density), order parameters, and wave function properties. In this article, the characteristics of excited state quantum phase transitions are investigated. The finite-size scaling behavior is determined at the mean-field level. It is found that excited state quantum phase transitions are universal to two-level bosonic and fermionic models with pairing interactions.

  15. Computing electronic structures: A new multiconfiguration approach for excited states

    SciTech Connect

    Cances, Eric . E-mail: cances@cermics.enpc.fr; Galicher, Herve . E-mail: galicher@cermics.enpc.fr; Lewin, Mathieu . E-mail: lewin@cermic.enpc.fr

    2006-02-10

    We present a new method for the computation of electronic excited states of molecular systems. This method is based upon a recent theoretical definition of multiconfiguration excited states [due to one of us, see M. Lewin, Solutions of the multiconfiguration equations in quantum chemistry, Arch. Rat. Mech. Anal. 171 (2004) 83-114]. Our algorithm, dedicated to the computation of the first excited state, always converges to a stationary state of the multiconfiguration model, which can be interpreted as an approximate excited state of the molecule. The definition of this approximate excited state is variational. An interesting feature is that it satisfies a non-linear Hylleraas-Undheim-MacDonald type principle: the energy of the approximate excited state is an upper bound to the true excited state energy of the N-body Hamiltonian. To compute the first excited state, one has to deform paths on a manifold, like this is usually done in the search for transition states between reactants and products on potential energy surfaces. We propose here a general method for the deformation of paths which could also be useful in other settings. We also compare our method to other approaches used in Quantum Chemistry and give some explanation of the unsatisfactory behaviours which are sometimes observed when using the latter. Numerical results for the special case of two-electron systems are provided: we compute the first singlet excited state potential energy surface of the H {sub 2} molecule.

  16. Proton release from Stentor photoreceptors in the excited states.

    PubMed Central

    Song, P S; Walker, E B; Auerbach, R A; Robinson, G W

    1981-01-01

    Steady-state and picosecond pulse excitations of the photophobic-phototactic receptors isolated from Stentor coeruleus produced anionic species predominantly in the excited singlet state, although neutral photoreceptors in the ground state were exclusively excited. The same photoreceptor in vivo also emits fluorescence from the excited state of its anionic species, with an excitation spectrum identical to the absorption spectrum of the neutral species in the ground state. The excited state dissociation of protons from the photoreceptor chromophore (stentorin; hypericin covalently linked to protein) efficiently occurs in less than 10 ps. A possible role of the transient-proton release from the photoreceptor, in the signal transduction photoresponse of Stentor, is briefly discussed. PMID:6791722

  17. Excited states in DNA strands investigated by ultrafast laser spectroscopy.

    PubMed

    Chen, Jinquan; Zhang, Yuyuan; Kohler, Bern

    2015-01-01

    Ultrafast laser experiments on carefully selected DNA model compounds probe the effects of base stacking, base pairing, and structural disorder on excited electronic states formed by UV absorption in single and double DNA strands. Direct π-orbital overlap between two stacked bases in a dinucleotide or in a longer single strand creates new excited states that decay orders of magnitude more slowly than the generally subpicosecond excited states of monomeric bases. Half or more of all excited states in single strands decay in this manner. Ultrafast mid-IR transient absorption experiments reveal that the long-lived excited states in a number of model compounds are charge transfer states formed by interbase electron transfer, which subsequently decay by charge recombination. The lifetimes of the charge transfer states are surprisingly independent of how the stacked bases are oriented, but disruption of π-stacking, either by elevating temperature or by adding a denaturing co-solvent, completely eliminates this decay channel. Time-resolved emission measurements support the conclusion that these states are populated very rapidly from initial excitons. These experiments also reveal the existence of populations of emissive excited states that decay on the nanosecond time scale. The quantum yield of these states is very small for UVB/UVC excitation, but increases at UVA wavelengths. In double strands, hydrogen bonding between bases perturbs, but does not quench, the long-lived excited states. Kinetic isotope effects on the excited-state dynamics suggest that intrastrand electron transfer may couple to interstrand proton transfer. By revealing how structure and non-covalent interactions affect excited-state dynamics, on-going experimental and theoretical studies of excited states in DNA strands can advance understanding of fundamental photophysics in other nanoscale systems.

  18. Excited-State Effective Masses in Lattice QCD

    SciTech Connect

    George Fleming, Saul Cohen, Huey-Wen Lin

    2009-10-01

    We apply black-box methods, i.e. where the performance of the method does not depend upon initial guesses, to extract excited-state energies from Euclidean-time hadron correlation functions. In particular, we extend the widely used effective-mass method to incorporate multiple correlation functions and produce effective mass estimates for multiple excited states. In general, these excited-state effective masses will be determined by finding the roots of some polynomial. We demonstrate the method using sample lattice data to determine excited-state energies of the nucleon and compare the results to other energy-level finding techniques.

  19. Systematics of α -decay transitions to excited states

    NASA Astrophysics Data System (ADS)

    Delion, D. S.; Dumitrescu, A.

    2015-08-01

    We systematize the available experimental material concerning α -decay transitions to low-lying excited states in even-even and odd-mass emitters. We generalize our previous theoretical prediction concerning the linear dependence between hindrance factors and the excitation energy for transitions in even-even α emitters. Thus, we show that α intensities for transitions to excited states depend linearly upon the excitation energy for all known even-even and odd-mass α emitters. It turns out that the well-known Viola-Seaborg law for α -decay transitions between ground states can be generalized for transitions to excited states. This rule can be used to predict any α -decay half-life to a low-lying excited state.

  20. The triplet excited state of Bodipy: formation, modulation and application.

    PubMed

    Zhao, Jianzhang; Xu, Kejing; Yang, Wenbo; Wang, Zhijia; Zhong, Fangfang

    2015-12-21

    Boron dipyrromethene (Bodipy) is one of the most extensively investigated organic chromophores. Most of the investigations are focused on the singlet excited state of Bodipy, such as fluorescence. In stark contrast, the study of the triplet excited state of Bodipy is limited, but it is an emerging area, since the triplet state of Bodipy is tremendously important for several areas, such as the fundamental photochemistry study, photodynamic therapy (PDT), photocatalysis and triplet-triplet annihilation (TTA) upconversion. The recent developments in the study of the production, modulation and application of the triplet excited state of Bodipy are discussed in this review article. The formation of the triplet state of Bodipy upon photoexcitation, via the well known approach such as the heavy atom effect (including I, Br, Ru, Ir, etc.), and the new methods, such as using a spin converter (e.g. C60), charge recombination, exciton coupling and the doubly substituted excited state, are summarized. All the Bodipy-based triplet photosensitizers show strong absorption of visible or near IR light and the long-lived triplet excited state, which are important for the application of the triplet excited state in PDT or photocatalysis. Moreover, the methods for switching (or modulation) of the triplet excited state of Bodipy were discussed, such as those based on the photo-induced electron transfer (PET), by controlling the competing Förster-resonance-energy-transfer (FRET), or the intermolecular charge transfer (ICT). Controlling the triplet excited state will give functional molecules such as activatable PDT reagents or molecular devices. It is worth noting that switching of the singlet excited state and the triplet state of Bodipy may follow different principles. Application of the triplet excited state of Bodipy in PDT, hydrogen (H2) production, photoredox catalytic organic reactions and TTA upconversion were discussed. The challenges and the opportunities in these areas were

  1. Experimental Investigation of Excited-State Lifetimes in Atomic Ytterbium

    SciTech Connect

    Bowers, C.J.; Budker, D.; Commins, E.D.; DeMille, D.; Freedman, S.J.; Nguyen, A.-T.; Shang, S.-Q.; Zolotorev, M.; /SLAC

    2011-11-15

    Lifetimes of 21 excited states in atomic Yb were measured using time-resolved fluorescence detection following pulsed laser excitation. The lifetime of the 4f{sup 14}5d6s {sup 3}D{sub 1} state, which is of particular importance for a proposed study of parity nonconservation in atoms, was measured to be 380(30) ns.

  2. Study of fuel systems for LH2-fueled subsonic transport aircraft, volume 1

    NASA Technical Reports Server (NTRS)

    Brewer, G. D.; Morris, R. E.; Davis, G. W.; Versaw, E. F.; Cunnington, G. R., Jr.; Riple, J. C.; Baerst, C. F.; Garmong, G.

    1978-01-01

    Several engine concepts examined to determine a preferred design which most effectively exploits the characteristics of hydrogen fuel in aircraft tanks received major emphasis. Many candidate designs of tank structure and cryogenic insulation systems were evaluated. Designs of all major elements of the aircraft fuel system including pumps, lines, valves, regulators, and heat exchangers received attention. Selected designs of boost pumps to be mounted in the LH2 tanks, and of a high pressure pump to be mounted on the engine were defined. A final design of LH2-fueled transport aircraft was established which incorporates a preferred design of fuel system. That aircraft was then compared with a conventionally fueled counterpart designed to equivalent technology standards.

  3. Development of advanced materials composites for use as insulations for LH2 tanks

    NASA Technical Reports Server (NTRS)

    Lemons, C. R.; Salmassy, O. K.

    1973-01-01

    A study of thread-reinforced polyurethane foam and glass fabric liner, serving as internally bonded insulation for space shuttle LH2 tanks, is reported. Emphasis was placed on an insulation system capable of reentry and multiple reuse in the shuttle environment. The optimized manufacturing parameters associated with each element of the composite are established and the results, showing successful completion of subscale system evaluation tests using the shuttle flight environmental requirements, are given.

  4. Charge-displacement analysis for excited states

    SciTech Connect

    Ronca, Enrico Tarantelli, Francesco; Pastore, Mariachiara Belpassi, Leonardo; De Angelis, Filippo; Angeli, Celestino; Cimiraglia, Renzo

    2014-02-07

    We extend the Charge-Displacement (CD) analysis, already successfully employed to describe the nature of intermolecular interactions [L. Belpassi et al., J. Am. Chem. Soc. 132, 13046 (2010)] and various types of controversial chemical bonds [L. Belpassi et al., J. Am. Chem. Soc. 130, 1048 (2008); N. Salvi et al., Chem. Eur. J. 16, 7231 (2010)], to study the charge fluxes accompanying electron excitations, and in particular the all-important charge-transfer (CT) phenomena. We demonstrate the usefulness of the new approach through applications to exemplary excitations in a series of molecules, encompassing various typical situations from valence, to Rydberg, to CT excitations. The CD functions defined along various spatial directions provide a detailed and insightful quantitative picture of the electron displacements taking place.

  5. Charge-displacement analysis for excited states

    NASA Astrophysics Data System (ADS)

    Ronca, Enrico; Pastore, Mariachiara; Belpassi, Leonardo; De Angelis, Filippo; Angeli, Celestino; Cimiraglia, Renzo; Tarantelli, Francesco

    2014-02-01

    We extend the Charge-Displacement (CD) analysis, already successfully employed to describe the nature of intermolecular interactions [L. Belpassi et al., J. Am. Chem. Soc. 132, 13046 (2010)] and various types of controversial chemical bonds [L. Belpassi et al., J. Am. Chem. Soc. 130, 1048 (2008); N. Salvi et al., Chem. Eur. J. 16, 7231 (2010)], to study the charge fluxes accompanying electron excitations, and in particular the all-important charge-transfer (CT) phenomena. We demonstrate the usefulness of the new approach through applications to exemplary excitations in a series of molecules, encompassing various typical situations from valence, to Rydberg, to CT excitations. The CD functions defined along various spatial directions provide a detailed and insightful quantitative picture of the electron displacements taking place.

  6. Excited-state dynamics of 3-hydroxyflavone anion in alcohols.

    PubMed

    Dereka, Bogdan; Letrun, Romain; Svechkarev, Denis; Rosspeintner, Arnulf; Vauthey, Eric

    2015-02-12

    The electronic absorption spectrum of 3-hydroxyflavone (3HF) in various solvents exhibits a long-wavelength (LW) band, whose origin has been debated. The excited-state dynamics of neutral and basic solutions of 3HF in alcohols upon excitation in this LW band has been investigated using a combination of fluorescence up-conversion and transient electronic and vibrational absorption spectroscopies. The ensemble of results reveals that, in neutral solutions, LW excitation results in the population of two excited species with similar fluorescence spectra but very different lifetimes, namely 40-100 ps and 2-3 ns, depending on the solvent. In basic solutions, the relative concentrations of these species change considerably in favor of that with the short-lived excited state. On the basis of the spectroscopic data and quantum chemistry calculations, the short lifetime is attributed to the excited state of 3HF anion, whereas the long one is tentatively assigned to an excited hydrogen-bonded complex with the solvent. Excited-state intermolecular proton transfer from the solvent to the anion yielding the tautomeric form of 3HF is not operative, as the excited anion decays to the ground state via an efficient nonradiative transition.

  7. The Evolution of Utilizing Manual Throttles to Avoid Low LH2 NPSP at the SSME Inlet

    NASA Technical Reports Server (NTRS)

    Henfling, Rick

    2011-01-01

    Even before the first flight of the Space Shuttle, it was understood low liquid hydrogen (LH2) Net Positive Suction Pressure (NPSP) at the inlet to the Space Shuttle Main Engine (SSME) can have adverse effects on engine operation. A number of failures within both the External Tank (ET) and the Orbiter Main Propulsion System could result in a low LH2 NPSP condition. Operational workarounds were developed to take advantage of the onboard crew s ability to manually throttle down the SSMEs, which alleviated the low LH2 NPSP condition. A throttling down of the SSME resulted in an increase in NPSP, mainly due to the reduction in frictional flow losses while at a lower throttle setting. As engineers refined their understanding of the NPSP requirements for the SSME (through a robust testing program), the operational techniques evolved to take advantage of these additional capabilities. Currently the procedure, which for early Space Shuttle missions required a Return-to-Launch-Site abort, now would result in a nominal Main Engine Cut Off (MECO) and no loss of mission objectives.

  8. Excited-State Deactivation of Branched Phthalocyanine Compounds.

    PubMed

    Zhu, Huaning; Li, Yang; Chen, Jun; Zhou, Meng; Niu, Yingli; Zhang, Xinxing; Guo, Qianjin; Wang, Shuangqing; Yang, Guoqiang; Xia, Andong

    2015-12-21

    The excited-state relaxation dynamics and chromophore interactions in two phthalocyanine compounds (bis- and trisphthalocyanines) are studied by using steady-state and femtosecond transient absorption spectral measurements, where the excited-state energy-transfer mechanism is explored. By exciting phthalocyanine compounds to their second electronically excited states and probing the subsequent relaxation dynamics, a multitude of deactivation pathways are identified. The transient absorption spectra show the relaxation pathway from the exciton state to excimer state and then back to the ground state in bisphthalocyanine (bis-Pc). In trisphthalocyanine (tris-Pc), the monomeric and dimeric subunits are excited and the excitation energy transfers from the monomeric vibrationally hot S1 state to the exciton state of a pre-associated dimer, with subsequent relaxation to the ground state through the excimer state. The theoretical calculations and steady-state spectra also show a face-to-face conformation in bis-Pc, whereas in tris-Pc, two of the three phthalocyanine branches form a pre-associated face-to-face dimeric conformation with the third one acting as a monomeric unit; this is consistent with the results of the transient absorption experiments from the perspective of molecular structure. The detailed structure-property relationships in phthalocyanine compounds is useful for exploring the function of molecular aggregates in energy migration of natural photosynthesis systems.

  9. Photoionization of ground and excited states of Ti I

    NASA Astrophysics Data System (ADS)

    Nahar, Sultana N.

    2015-07-01

    Detailed photoionization of ground and many excited states with autoionizing resonances of neutral Ti are presented. Ti I with 22 electrons forms a large number of bound states, the present work finds a total of 908 bound states with n ⩽ 10 and l ⩽ 8 . Photoionization cross sections (σPI) for all these bound states have been obtained. Calculations were carried out in the close-coupling R-matrix method using a wave function expansion that included 36 states of core ion Ti II. It is found that the resonances enhance the low energy region of photoionization of the ground and low lying excited states. The resonant features will increase the opacity, as expected of astrophysical observation, and hence play important role in determination of abundances in the elements in the astronomical objects. The excited states also show prominent structures of Seaton or photo-excitation-of-core resonances.

  10. Excitation of weakly bound molecules to trilobitelike Rydberg states.

    PubMed

    Bellos, M A; Carollo, R; Banerjee, J; Eyler, E E; Gould, P L; Stwalley, W C

    2013-08-01

    We observe "trilobitelike" states of ultracold (85)Rb(2) molecules, in which a ground-state atom is bound by the electronic wave function of its Rydberg-atom partner. We populate these states through the ultraviolet excitation of weakly bound molecules, and access a regime of trilobitelike states at low principal quantum numbers and with vibrational turning points around 35 Bohr radii. This demonstrates that, unlike previous studies that used free-to-bound transitions, trilobitelike states can also be excited through bound-to-bound transitions. This approach provides high excitation probabilities without requiring high-density samples, and affords the ability to control the excitation radius by selection of the initial-state vibrational level.

  11. Spectroscopic studies of two spectral variants of light-harvesting complex 2 (LH2) from the photosynthetic purple sulfur bacterium Allochromatium vinosum.

    PubMed

    Niedzwiedzki, Dariusz M; Bina, David; Picken, Nichola; Honkanen, Suvi; Blankenship, Robert E; Holten, Dewey; Cogdell, Richard J

    2012-09-01

    Two spectral forms of the peripheral light-harvesting complex (LH2) from the purple sulfur photosynthetic bacterium Allochromatium vinosum were purified and their photophysical properties characterized. The complexes contain bacteriochlorophyll a (BChl a) and multiple species of carotenoids. The composition of carotenoids depends on the light conditions applied during growth of the cultures. In addition, LH2 grown under high light has a noticeable split of the B800 absorption band. The influence of the change of carotenoid distribution as well as the spectral change of the excitonic absorption of the bacteriochlorophylls on the light-harvesting ability was studied using steady-state absorption, fluorescence and femtosecond time-resolved absorption at 77K. The results demonstrate that the change of the distribution of the carotenoids when cells were grown at low light adapts the absorptive properties of the complex to the light conditions and maintains maximum photon-capture performance. In addition, an explanation for the origin of the enigmatic split of the B800 absorption band is provided. This spectral splitting is also observed in LH2 complexes from other photosynthetic sulfur purple bacterial species. According to results obtained from transient absorption spectroscopy, the B800 band split originates from two spectral forms of the associated BChl a monomeric molecules bound within the same complex.

  12. Disentangling intrinsic ultrafast excited-state dynamics of cytosine tautomers.

    PubMed

    Ho, Jr-Wei; Yen, Hung-Chien; Chou, Wei-Kuang; Weng, Chih-Nan; Cheng, Li-Hao; Shi, Hui-Qi; Lai, Szu-Hsueh; Cheng, Po-Yuan

    2011-08-01

    Gas-phase ultrafast excited-state dynamics of cytosine, 1-methylcytosine, and 5-fluorocytosine were investigated in molecular beams using femtosecond pump-probe photoionization spectroscopy to identify the intrinsic dynamics of the major cytosine tautomers. The results indicate that, upon photoexcitation in the first absorption band, the cytosine enol tautomer exhibits a significantly longer excited-state lifetime than its keto and imino counterparts. The initially excited states of the cytosine keto and imino tautomers decay with sub-picosecond dynamics for excitation wavelengths shorter than 300 nm, whereas that of the cytosine enol tautomer decays with time constants ranging from 3 to 45 ps for excitation between 260 and 285 nm.

  13. Study of excited nucleon states at EBAC: status and plans

    SciTech Connect

    Hiroyuki Kamano

    2009-12-01

    We present an overview of a research program for the excited nucleon states in Excited Baryon Analysis Center (EBAC) at Jefferson Lab. Current status of our analysis of the meson production reactions based on the unitary dynamical coupled-channels model is summarized, and the N* pole positions extracted from the constructed scattering amplitudes are presented. Our plans for future developments are also discussed.

  14. Excited-State Dynamics in Folic Acid and 6-CARBOXYPTERIN upon Uva Excitation

    NASA Astrophysics Data System (ADS)

    Huang, Huijuan; Vogt, R. Aaron; Crespo-Hernandez, Carlos E.

    2013-06-01

    The excited-state dynamics of folic acid (FA) and 6-carboxypterin (6CP) are poorly understood and work is needed to uncover the relaxation pathways that ultimately lead to their oxidative damage of DNA. In our approach, broad-band transient absorption spectroscopy was used to monitor the evolution of the excited states in FA and 6CP in basic aqueous solution upon excitation at 350 nm. In addition, quantum-chemical calculations were performed to assist in the interpretation of the experimental results and in the postulation of kinetic mechanisms. The combined experimental and computational results support a kinetic model where excitation of FA results in ultrafast charge separation (τ = 0.6 ps), which decays back to the ground state primarily by charge recombination with a lifetime of 2.2 ps. A small fraction of the charge transfer state undergoes intersystem crossing to populate the lowest-energy triplet state with a lifetime of 200 ps. On the other hand, a large fraction of the initially excited singlet state in 6CP decays by fluorescence emission with a lifetime of 100 ps, while intersystem crossing to the triplet state occurs with a lifetime of 4.4 ns. The potential implications of these results to the oxidative damage of DNA by FA and 6CP will be discussed. Funding from the National Science Foundation is gratefully acknowledged (CHE-1255084).

  15. A note on calm excited states of inflation

    SciTech Connect

    Ashoorioon, Amjad; Shiu, Gary E-mail: shiu@physics.wisc.edu

    2011-03-01

    We identify a two-parameter family of excited states within slow-roll inflation for which either the corrections to the two-point function or the characteristic signatures of excited states in the three-point function — i.e. the enhancement for the flattened momenta configurations– are absent. These excited states may nonetheless violate the adiabaticity condition maximally. We dub these initial states of inflation calm excited states. We show that these two sets do not intersect, i.e., those that leave the power-spectrum invariant can be distinguished from their bispectra, and vice versa. The same set of calm excited states that leave the two-point function invariant for slow-roll inflation, do the same task for DBI inflation. However, at the level of three-point function, the calm excited states whose flattened configuration signature is absent for slow-roll inflation, will lead to an enhancement for DBI inflation generally, although the signature is smaller than what suggested by earlier analysis. This example also illustrates that imposing the Wronskian condition is important for obtaining a correct estimate of the non-Gaussian signatures.

  16. Vibronic coupling in the excited-states of carotenoids.

    PubMed

    Miki, Takeshi; Buckup, Tiago; Krause, Marie S; Southall, June; Cogdell, Richard J; Motzkus, Marcus

    2016-04-28

    The ultrafast femtochemistry of carotenoids is governed by the interaction between electronic excited states, which has been explained by the relaxation dynamics within a few hundred femtoseconds from the lowest optically allowed excited state S2 to the optically dark state S1. Extending this picture, some additional dark states (3A(g)(-) and 1B(u)(-)) and their interaction with the S2 state have also been suggested to play a major role in the ultrafast deactivation of carotenoids and their properties. Here, we investigate the interaction between such dark and bright electronic excited states of open chain carotenoids, particularly its dependence on the number of conjugated double bonds (N). We focus on the ultrafast wave packet motion on the excited potential surface, which is modified by the interaction between bright and dark electronic states. Such a coupling between electronic states leads to a shift of the vibrational frequency during the excited-state evolution. In this regard, pump-degenerate four-wave mixing (pump-DFWM) is applied to a series of carotenoids with different numbers of conjugated double bonds N = 9, 10, 11 and 13 (neurosporene, spheroidene, lycopene and spirilloxanthin, respectively). Moreover, we demonstrate in a closed-chain carotenoid (lutein) that the coupling strength and therefore the vibrational shift can be tailored by changing the energy degeneracy between the 1B(u)(+) and 1B(u)(-) states via solvent interaction.

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

    NASA Astrophysics Data System (ADS)

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

    2009-07-01

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

  18. CFD investigation of thermal and pressurization performance in LH2 tank during discharge

    NASA Astrophysics Data System (ADS)

    Wang, Lei; Li, Yanzhong; Li, Cui; Zhao, Zhixiang

    2013-10-01

    Predictions of thermal and pressurization performance in a liquid hydrogen (LH2) tank during liquid discharge is of significance to the design and optimization of a rocket pressurization system. In this paper, a computational fluid dynamic (CFD) model is introduced to simulate the pressurized discharge event of LH2 tank. The wall region together with the fluid region is simultaneously considered as the computational domain, and low-Re k-ε model is applied to account for the fluid-wall heat exchange effect. Liquid-vapor phase change effect is also involved in the model. Comparison of the numerical results with existing experimental data suggests that the CFD model has a good adaptability in pressurization computation. Detailed characteristics, such as pressurant gas requirement, pressure altering history, and temperature distribution inside the tank, can be obtained by the model. The difference of pressurant gas, selecting helium or vapor H2, may result in the variations in pressure and temperature histories. Pressurization by vapor H2 supplies a higher pressure and also a temperature rise, which is significant to consider the selection of pressurant gas. The influences of phase change effect and injector structure on pressurization behaviors are also analyzed. The computational results show that liquid-vapor phase change has a slight influence on the pressurization behaviors. Significant pressure decay at the beginning stage of process may occur in the case of no-diffuser injector application since the incoming gas is excessively cooled by cold LH2. The results show that the present CFD model has a good adaptability in the prediction of pressurization behaviors and is a useful tool for the design and optimization of a pressurization system.

  19. Peroxyacetyl radical: Electronic excitation energies, fundamental vibrational frequencies, and symmetry breaking in the first excited state

    SciTech Connect

    Copan, Andreas V.; Wiens, Avery E.; Nowara, Ewa M.; Schaefer, Henry F.; Agarwal, Jay

    2015-02-07

    Peroxyacetyl radical [CH{sub 3}C(O)O{sub 2}] is among the most abundant peroxy radicals in the atmosphere and is involved in OH-radical recycling along with peroxyacetyl nitrate formation. Herein, the ground (X{sup ~}) and first (A{sup ~}) excited state surfaces of cis and trans peroxyacetyl radical are characterized using high-level ab initio methods. Geometries, anharmonic vibrational frequencies, and adiabatic excitation energies extrapolated to the complete basis-set limit are reported from computations with coupled-cluster theory. Excitation of the trans conformer is found to induce a symmetry-breaking conformational change due to second-order Jahn-Teller interactions with higher-lying excited states. Additional benchmark computations are provided to aid future theoretical work on peroxy radicals.

  20. Characterizing RNA Excited States Using NMR Relaxation Dispersion.

    PubMed

    Xue, Yi; Kellogg, Dawn; Kimsey, Isaac J; Sathyamoorthy, Bharathwaj; Stein, Zachary W; McBrairty, Mitchell; Al-Hashimi, Hashim M

    2015-01-01

    Changes in RNA secondary structure play fundamental roles in the cellular functions of a growing number of noncoding RNAs. This chapter describes NMR-based approaches for characterizing microsecond-to-millisecond changes in RNA secondary structure that are directed toward short-lived and low-populated species often referred to as "excited states." Compared to larger scale changes in RNA secondary structure, transitions toward excited states do not require assistance from chaperones, are often orders of magnitude faster, and are localized to a small number of nearby base pairs in and around noncanonical motifs. Here, we describe a procedure for characterizing RNA excited states using off-resonance R1ρ NMR relaxation dispersion utilizing low-to-high spin-lock fields (25-3000 Hz). R1ρ NMR relaxation dispersion experiments are used to measure carbon and nitrogen chemical shifts in base and sugar moieties of the excited state. The chemical shift data are then interpreted with the aid of secondary structure prediction to infer potential excited states that feature alternative secondary structures. Candidate structures are then tested by using mutations, single-atom substitutions, or by changing physiochemical conditions, such as pH and temperature, to either stabilize or destabilize the candidate excited state. The resulting chemical shifts of the mutants or under different physiochemical conditions are then compared to those of the ground and excited states. Application is illustrated with a focus on the transactivation response element from the human immune deficiency virus type 1, which exists in dynamic equilibrium with at least two distinct excited states. PMID:26068737

  1. A simple formula for the energies of doubly excited states

    SciTech Connect

    Lin, C.D.; Watanabe, S.

    1986-11-01

    A simple formula for the energy levels of doubly excited states of atoms and multiply charged ions is derived and expressed in terms of a set of new correlation quantum numbers. The accuracy of the formula is checked by comparing with the results from other elaborate calculations. Modification of the formula for doubly excited states of multielectron atoms are also presented. 12 refs., 2 tabs.

  2. Characterizing RNA Excited States Using NMR Relaxation Dispersion.

    PubMed

    Xue, Yi; Kellogg, Dawn; Kimsey, Isaac J; Sathyamoorthy, Bharathwaj; Stein, Zachary W; McBrairty, Mitchell; Al-Hashimi, Hashim M

    2015-01-01

    Changes in RNA secondary structure play fundamental roles in the cellular functions of a growing number of noncoding RNAs. This chapter describes NMR-based approaches for characterizing microsecond-to-millisecond changes in RNA secondary structure that are directed toward short-lived and low-populated species often referred to as "excited states." Compared to larger scale changes in RNA secondary structure, transitions toward excited states do not require assistance from chaperones, are often orders of magnitude faster, and are localized to a small number of nearby base pairs in and around noncanonical motifs. Here, we describe a procedure for characterizing RNA excited states using off-resonance R1ρ NMR relaxation dispersion utilizing low-to-high spin-lock fields (25-3000 Hz). R1ρ NMR relaxation dispersion experiments are used to measure carbon and nitrogen chemical shifts in base and sugar moieties of the excited state. The chemical shift data are then interpreted with the aid of secondary structure prediction to infer potential excited states that feature alternative secondary structures. Candidate structures are then tested by using mutations, single-atom substitutions, or by changing physiochemical conditions, such as pH and temperature, to either stabilize or destabilize the candidate excited state. The resulting chemical shifts of the mutants or under different physiochemical conditions are then compared to those of the ground and excited states. Application is illustrated with a focus on the transactivation response element from the human immune deficiency virus type 1, which exists in dynamic equilibrium with at least two distinct excited states.

  3. Development of advanced materials composites for use as insulations for LH2 tanks

    NASA Technical Reports Server (NTRS)

    Lemons, C. R.; Watts, C. R.; Salmassy, O. K.

    1972-01-01

    A study of internal insulation materials and fabrication processes for space shuttle LH2 tanks is reported. Emphasis was placed on an insulation system capable of reentry and multiple reuse in the Shuttle environment. Results are given on the optimization and manufacturing process scale-up of a 3D fiberreinforced foam insulation, BX-251-3D, derived from the Saturn S-4B internal insulation. It is shown that BX-251-3D can be satisfactorily installed in large-scale tanks under conditions that will permit a significant cost saving over the existing S-4B technology.

  4. Electron-impact excitation and ionization cross sections for ground state and excited helium atoms

    SciTech Connect

    Ralchenko, Yu. Janev, R.K.; Kato, T.; Fursa, D.V.; Bray, I.; Heer, F.J. de

    2008-07-15

    Comprehensive and critically assessed cross sections for the electron-impact excitation and ionization of ground state and excited helium atoms are presented. All states (atomic terms) with n{<=}4 are treated individually, while the states with n{>=}5 are considered degenerate. For the processes involving transitions to and from n{>=}5 levels, suitable cross section scaling relations are presented. For a large number of transitions, from both ground and excited states, convergent close coupling calculations were performed to achieve a high accuracy of the data. The evaluated/recommended cross section data are presented by analytic fit functions, which preserve the correct asymptotic behavior of the cross sections. The cross sections are also displayed in graphical form.

  5. Investigation into chromophore excited-state coupling in allophycocyanin

    NASA Astrophysics Data System (ADS)

    Zheng, Xiguang; Zhao, Fuli; Wang, He Z.; Gao, Zhaolan; Yu, Zhenxin; Zhu, Jinchang; Xia, Andong; Jiang, Lijin

    1994-08-01

    Both theoretical and experimental studies are presented on chromophore excited-state coupling in linker-free allophycocyanin (APC), one of the antenna phycobiliproteins in algal photosynthesis. A three-site-coupling model has been introduced to describe the exciton interaction mechanism amoung the excited (beta) chromophore in APC, and the exciton energy splitting is estimated. Picosecond polarized fluorescence experiments both on monomeric and trimeric APC isolated from alga Spirulina platensis have been performed. The experimental results show that APC monomer and trimer exhibit remarkedly different spectropic characteristics, and satisfy the suggestion of strong excited- state coupling among chromophores in APC.

  6. Characterizing RNA Excited States using NMR Relaxation Dispersion

    PubMed Central

    Xue, Yi; Kellogg, Dawn; Kimsey, Isaac J; Sathyamoorthy, Bharathwaj; Stein, Zachary W; McBrairty, Mitchell; Al-Hashimi, Hashim M.

    2016-01-01

    Changes in RNA secondary structure play fundamental roles in the cellular functions of a growing number of non-coding RNAs. This chapter describes NMR-based approaches for characterizing microsecond-to-millisecond changes in RNA secondary structure that are directed toward short-lived and low-populated species often referred to as “excited states”. Compared to larger-scale changes in RNA secondary structure, transitions towards excited states do not require assistance from chaperones, are often orders of magnitude faster, and are localized to a small number of nearby base pairs in and around non-canonical motifs. Here we describe a procedure for characterizing RNA excited states using off-resonance R1ρ NMR relaxation dispersion utilizing low-to-high spin-lock fields (25–3000 Hz). R1ρ NMR relaxation dispersion experiments are used to measure carbon and nitrogen chemical shifts in base and sugar moieties of the excited state. The chemical shift data is then interpreted with the aid of secondary structure prediction to infer potential excited states that feature alternative secondary structures. Candidate structures are then tested by using mutations, single-atom substitutions, or by changing physiochemical conditions, such as pH and temperature, to either stabilize or destabilize the candidate excited state. The resulting chemical shifts of the mutants or under different physiochemical conditions are then compared to those of the ground and excited state. Application is illustrated with a focus on the transactivation response element (TAR) from the human immune deficiency virus type 1 (HIV-1), which exists in dynamic equilibrium with at least two distinct excited states. PMID:26068737

  7. Microwave spectroscopy of furfural in vibrationally excited states

    NASA Astrophysics Data System (ADS)

    Motiyenko, R. A.; Alekseev, E. A.; Dyubko, S. F.

    2007-07-01

    The results of microwave spectrum investigation of the excited vibrational states of furfural in the frequency range between 49 and 149 GHz are reported. In total 15 excited vibrational states (9 for trans-furfural and 6 for cis-furfural) were assigned and analyzed. Six of the 15 investigated states were assigned for the first time. Accurate values of rigid rotor and quartic centrifugal distortion constants of asymmetric top Hamiltonian have been determined for 13 excited states. Also for some states several sextic and octic level constants were needed in order to fit the data within experimental accuracy. The vt = 3 and vs = 1, va = 1 states of trans-furfural were found to be strongly perturbed and only rotational transitions with low Ka values can be reliably identified in this study.

  8. Excited States of the divacancy in SiC

    NASA Astrophysics Data System (ADS)

    Bockstedte, Michel; Garratt, Thomas; Ivady, Viktor; Gali, Adam

    2014-03-01

    The divacancy in SiC - a technologically mature material that fulfills the necessary requirements for hosting defect based quantum computing - is a good candidate for implementing a solid state quantum bit. Its ground state is isovalent to the NV center in diamond as demonstrated by density functional theory (DFT). Furthermore, coherent manipulation of divacancy spins in SiC has been demonstrated. The similarities to NV might indicate that the same inter system crossing (ICS) from the high to the low spin state is responsible for its spin-dependent fluorescent signal. By DFT and a DFT-based multi-reference hamiltonian we analyze the excited state spectrum of the defects. In contrast to the current picture of the spin dynamics of the NV center, we predict that a static Jahn-Teller effect in the first excited triplet states governs an ICS both with the excited and ground state of the divacancy.

  9. Neutral Excitations in the Gaffnian state

    NASA Astrophysics Data System (ADS)

    Kang, Byungmin; Moore, Joel E.

    The Fractional Quantum Hall Effect (FQHE) is one of the most well-studied systems having topological order. Starting with the pioneering work by Laughlin, the model wave function approach has been shown to provide essential information for understanding topological order in gapped incompressible states. We study a model wave function called the Gaffnian state which is believed to represent a gapless, strongly correlated state that is very different from conventional metals. To understand this exotic gapless state better, we provide a representation in which the pairing structure of the Gaffnian state becomes more explicit. We employ the single-mode approximation of the Girvin-MacDonald-Platzman (GMP) mode, which is a neutral collective exitation mode, in order to have a physical picture of the gaplessness of the Gaffnian state. In particular, we discuss how to extract systematically the relevant physics in the long-distance, large electron number limit of the FQH states using a numerical calculation with relatively few electrons.

  10. Dual state antiphase excitability in optically injected quantum dot lasers

    NASA Astrophysics Data System (ADS)

    Kelleher, B.; Goulding, D.; Tykalewicz, B.; Fedorov, N.; Dubinkin, I.; Hegarty, S. P.; Huyet, G.; Erneux, T.; Viktorov, E. A.

    2016-04-01

    Depending on device and operating parameters, the emission of lasers based on InAs quantum dot (QD) material may come from the ground state (GS) only, from the first excited state (ES) only or simultaneously from both states. When the emission is from the ES only, optical injection at the GS frequency can completely suppress the ES output and instead, phase-locked emission from the GS can be obtained. We report on a variety of non-linear phenomena obtained when the frequency of the master laser is varied revealing two antiphase, dual-state excitable regimes.

  11. First observation of excited states in Li12

    NASA Astrophysics Data System (ADS)

    Hall, C. C.; Lunderberg, E. M.; Deyoung, P. A.; Baumann, T.; Bazin, D.; Blanchon, G.; Bonaccorso, A.; Brown, B. A.; Brown, J.; Christian, G.; Denby, D. H.; Finck, J.; Frank, N.; Gade, A.; Hinnefeld, J.; Hoffman, C. R.; Luther, B.; Mosby, S.; Peters, W. A.; Spyrou, A.; Thoennessen, M.

    2010-02-01

    The neutron-unbound ground state and two excited states of Li12 were formed by the two-proton removal reaction from a 53.4-MeV/u B14 beam. The decay energy spectrum of Li12 was measured with the Modular Neutron Array (MoNA) and the Sweeper dipole superconducting magnet at the National Superconducting Cyclotron Laboratory. Two excited states at resonance energies of 250 ± 20 keV and 555 ± 20 keV were observed for the first time and the data are consistent with the previously reported s-wave ground state with a scattering length of as=-13.7 fm.

  12. Lifetime and g-factor measurements of excited states using Coulomb excitation and alpha transfer reactions

    NASA Astrophysics Data System (ADS)

    Guevara, Z. E.; Torres, D. A.

    2016-07-01

    In this contribution the challenges in the use of a setup to simultaneously measure lifetimes and g-factor values will be presented. The simultaneous use of the transient field technique and the Doppler Shift Attenuation Method, to measure magnetic moments and lifetimes respectively, allows to obtain a complete characterization of the currents of nucleons and the deformation in excited states close to the ground state. The technique is at the moment limited to Coulomb excitation and alpha-transfer reactions, what opens an interesting perspective to consider this type of experiments with radioactive beams. The use of deep-inelastic and fusion-evaporation reactions will be discussed. An example of a setup that makes use of a beam of 106Cd to study excited states of 110Sn and the beam nuclei itself will be presented.

  13. Development and validation of cryogenic foam insulation for LH2 subsonic transports

    NASA Technical Reports Server (NTRS)

    Anthony, F. M.; Colt, J. Z.; Helenbrook, R. G.

    1981-01-01

    Fourteen foam insulation specimens were tested. Some were plain foam while others contained flame retardants, chopped fiberglass reinforcement and/or vapor barriers. The thermal performance of the insulation was determined by measuring the rate at which LH2 boiled from an aluminum tank insulated with the test material. The test specimens were approximately 50 mm (2 in.) thick. They were structurally scaled so that the test cycle would duplicate the maximum thermal stresses predicted for the thicker insulation of an aircraft liquid hydrogen fuel tank during a typical subsonic flight. The simulated flight cycle of approximately 10 minutes duration heated the other insulation surface to 316 K (110 F) and cooled it to 226 K (20 F) while the inner insulation surface remained at liquid hydrogen temperature of 20 K (-423 F). Two urethane foam insulations exceeded the initial life goal of 2400 simulated flight cycles and sustained 4400 cycles with only minor damage. The addition of fiberglass reinforcement of flame retardant materials to an insulation degraded thermal performance and/or the life of the foam material. Installation of vapor barriers enhanced the structural integrity of the material but did not improve thermal performance. All of the foams tested were available materials; none were developed specifically for LH2 service.

  14. An experimental study of a small high speed LH2 rocket pump: Fundamental mechanical design

    NASA Astrophysics Data System (ADS)

    Kikuchi, Masataka; Suzuki, Mineo; Shimura, Takashi; Watanabe, Mitsuo; Kamijo, Kenjiro; Nosaka, Masataka; Warashina, Shougo

    1991-09-01

    A small high speed Liquid Hydrogen (LH2) pump was designed, fabricated, and tested in order to obtain technical data necessary for the development of upper stage rocket engines, e.g., the LE-5 and Orbiter Transfer Vehicle (OTV) engines. The pump's basic mechanical design is described, as well as its mechanical performance during tests using LH2 (both at nominal operating and rapid start and stop conditions). It was confirmed that the same materials employed for liquid oxygen pump components can be used, except for the impeller. An impeller made of titanium alloy (Ti-5Al-2.5Sn) was machined and then diffusion bonded, and subsequently withstood a high speed operating condition (50,000 rpm) for 350 sec. A balance piston configuration was selected for axial thrust control, where the impeller acts as a balance disk. The piston's performance was satisfactory, although the impeller's balance position during the tests was different from design calculations. Post-test examinations revealed light rubbing traces on the impeller and casing at the balance piston orifice. This positional discrepancy was caused by an inaccurate estimate of the orifice flow coefficients and leakage flow rate. Stress analysis on other components and machine specifications for critical mating parts were also verified as satisfactory. Self lubricated ball bearings and rotating shaft seals showed adequate performance. Results indicate that smooth operation was achieved, thus confirming the soundness of the pump's mechanical design.

  15. Orbiter LH2 Feedline Flowliner Cracking Problem. Version 1.0

    NASA Technical Reports Server (NTRS)

    Harris, Charles E.; Cragg, Clinton H.; Raju, Ivatury S.; Elliot, Kenny B.; Madaras, Eric I.; Piascik, Robert S.; Halford, Gary R.; Bonacuse, Peter J.; Sutliff, Daniel L.; Bakhle, Milind A.

    2005-01-01

    In May of 2002, three cracks were found in the downstream flowliner at the gimbal joint in the LH2 feedline at the interface with the Low Pressure Fuel Turbopump (LPFP) of Space Shuttle Main Engine (SSME) #1 of Orbiter OV-104. Subsequent inspections of the feedline flowliners in the other orbiters revealed the existence of 8 additional cracks. No cracks were found in the LO2 feedline flowliners. A solution to the cracking problem was developed and implemented on all orbiters. The solution included weld repair of all detectable cracks and the polishing of all slot edges to remove manufacturing discrepancies that could initiate new cracks. Using the results of a fracture mechanics analysis with a scatter factor of 4 on the predicted fatigue life, the orbiters were cleared for return to flight with a one-flight rationale requiring inspections after each flight. OV-104 flew mission STS-112 and OV-105 flew mission STS-113. The post-flight inspections did not find any cracks in the repaired flowliners. At the request of the Orbiter Program, the NESC conducted an assessment of the Orbiter LH2 Feedline Flowliner cracking problem with a team of subject matter experts from throughout NASA.

  16. Direct observation of photoinduced bent nitrosyl excited-state complexes

    SciTech Connect

    Sawyer, Karma R.; Steele, Ryan P.; Glascoe, Elizabeth A.; Cahoon, James F.; Schlegel, Jacob P.; Head-Gordon, Martin; Harris, Charles B.

    2008-06-28

    Ground state structures with side-on nitrosyl ({eta}{sup 2}-NO) and isonitrosyl (ON) ligands have been observed in a variety of transition-metal complexes. In contrast, excited state structures with bent-NO ligands have been proposed for years but never directly observed. Here we use picosecond time-resolved infrared spectroscopy and density functional theory (DFT) modeling to study the photochemistry of Co(CO){sub 3}(NO), a model transition-metal-NO compound. Surprisingly, we have observed no evidence for ON and {eta}{sup 2}-NO structural isomers, but have observed two bent-NO complexes. DFT modeling of the ground and excited state potentials indicates that the bent-NO complexes correspond to triplet excited states. Photolysis of Co(CO){sub 3}(NO) with a 400-nm pump pulse leads to population of a manifold of excited states which decay to form an excited state triplet bent-NO complex within 1 ps. This structure relaxes to the ground triplet state in ca. 350 ps to form a second bent-NO structure.

  17. The excited state antiaromatic benzene ring: a molecular Mr Hyde?

    PubMed

    Papadakis, Raffaello; Ottosson, Henrik

    2015-09-21

    The antiaromatic character of benzene in its first ππ* excited triplet state (T1) was deduced more than four decades ago by Baird using perturbation molecular orbital (PMO) theory [J. Am. Chem. Soc. 1972, 94, 4941], and since then it has been confirmed through a range of high-level quantum chemical calculations. With focus on benzene we now first review theoretical and computational studies that examine and confirm Baird's rule on reversal in the electron count for aromaticity and antiaromaticity of annulenes in their lowest triplet states as compared to Hückel's rule for the ground state (S0). We also note that the rule according to quantum chemical calculations can be extended to the lowest singlet excited state (S1) of benzene. Importantly, Baird, as well as Aihara [Bull. Chem. Soc. Jpn. 1978, 51, 1788], early put forth that the destabilization and excited state antiaromaticity of the benzene ring should be reflected in its photochemical reactivity, yet, today these conclusions are often overlooked. Thus, in the second part of the article we review photochemical reactions of a series of benzene derivatives that to various extents should stem from the excited state antiaromatic character of the benzene ring. We argue that benzene can be viewed as a molecular "Dr Jekyll and Mr Hyde" with its largely unknown excited state antiaromaticity representing its "Mr Hyde" character. The recognition of the "Jekyll and Hyde" split personality feature of the benzene ring can likely be useful in a range of different areas. PMID:25960203

  18. The excited state antiaromatic benzene ring: a molecular Mr Hyde?

    PubMed

    Papadakis, Raffaello; Ottosson, Henrik

    2015-09-21

    The antiaromatic character of benzene in its first ππ* excited triplet state (T1) was deduced more than four decades ago by Baird using perturbation molecular orbital (PMO) theory [J. Am. Chem. Soc. 1972, 94, 4941], and since then it has been confirmed through a range of high-level quantum chemical calculations. With focus on benzene we now first review theoretical and computational studies that examine and confirm Baird's rule on reversal in the electron count for aromaticity and antiaromaticity of annulenes in their lowest triplet states as compared to Hückel's rule for the ground state (S0). We also note that the rule according to quantum chemical calculations can be extended to the lowest singlet excited state (S1) of benzene. Importantly, Baird, as well as Aihara [Bull. Chem. Soc. Jpn. 1978, 51, 1788], early put forth that the destabilization and excited state antiaromaticity of the benzene ring should be reflected in its photochemical reactivity, yet, today these conclusions are often overlooked. Thus, in the second part of the article we review photochemical reactions of a series of benzene derivatives that to various extents should stem from the excited state antiaromatic character of the benzene ring. We argue that benzene can be viewed as a molecular "Dr Jekyll and Mr Hyde" with its largely unknown excited state antiaromaticity representing its "Mr Hyde" character. The recognition of the "Jekyll and Hyde" split personality feature of the benzene ring can likely be useful in a range of different areas.

  19. Photocyclization Reactions of Diarylethenes via the Excited Triplet State.

    PubMed

    Murata, Ryutaro; Yago, Tomoaki; Wakasa, Masanobu

    2015-11-12

    Cyclization reactions of three diarylethene derivatives, 1,2-bis(2-methyl-3-benzothienyl)perfluorocyclopentene (BT), 1,2-bis(2-hexyl-3-benzothienyl)perfluorocyclopentene (BTHex), and 1,2-bis(2-isopropyl-3-benzothienyl)perfluorocyclopentene (BTiPr), via their excited triplet states were studied by means of steady-state and nanosecond transient absorption spectroscopy. The excited triplet states of BT, BTHex, and BTiPr were generated by energy transfer from the photoexcited triplet states of sensitizers such as xanthone, phenanthrene, and pyrene. The single-step quantum yields of the cyclization reactions from the excited triplet states of BT, BTHex, and BTiPr were determined to be 0.34, 0.53, and 0.65, respectively. The triplet energies of these three BTs were estimated to be 190-200 kJ mol(-1). PMID:26490486

  20. Controlling chimera states: The influence of excitable units.

    PubMed

    Isele, Thomas; Hizanidis, Johanne; Provata, Astero; Hövel, Philipp

    2016-02-01

    We explore the influence of a block of excitable units on the existence and behavior of chimera states in a nonlocally coupled ring-network of FitzHugh-Nagumo elements. The FitzHugh-Nagumo system, a paradigmatic model in many fields from neuroscience to chemical pattern formation and nonlinear electronics, exhibits oscillatory or excitable behavior depending on the values of its parameters. Until now, chimera states have been studied in networks of coupled oscillatory FitzHugh-Nagumo elements. In the present work, we find that introducing a block of excitable units into the network may lead to several interesting effects. It allows for controlling the position of a chimera state as well as for generating a chimera state directly from the synchronous state.

  1. Controlling chimera states: The influence of excitable units

    NASA Astrophysics Data System (ADS)

    Isele, Thomas; Hizanidis, Johanne; Provata, Astero; Hövel, Philipp

    2016-02-01

    We explore the influence of a block of excitable units on the existence and behavior of chimera states in a nonlocally coupled ring-network of FitzHugh-Nagumo elements. The FitzHugh-Nagumo system, a paradigmatic model in many fields from neuroscience to chemical pattern formation and nonlinear electronics, exhibits oscillatory or excitable behavior depending on the values of its parameters. Until now, chimera states have been studied in networks of coupled oscillatory FitzHugh-Nagumo elements. In the present work, we find that introducing a block of excitable units into the network may lead to several interesting effects. It allows for controlling the position of a chimera state as well as for generating a chimera state directly from the synchronous state.

  2. Nature of ground and electronic excited states of higher acenes.

    PubMed

    Yang, Yang; Davidson, Ernest R; Yang, Weitao

    2016-08-30

    Higher acenes have drawn much attention as promising organic semiconductors with versatile electronic properties. However, the nature of their ground state and electronic excited states is still not fully clear. Their unusual chemical reactivity and instability are the main obstacles for experimental studies, and the potentially prominent diradical character, which might require a multireference description in such large systems, hinders theoretical investigations. Here, we provide a detailed answer with the particle-particle random-phase approximation calculation. The (1)Ag ground states of acenes up to decacene are on the closed-shell side of the diradical continuum, whereas the ground state of undecacene and dodecacene tilts more to the open-shell side with a growing polyradical character. The ground state of all acenes has covalent nature with respect to both short and long axes. The lowest triplet state (3)B2u is always above the singlet ground state even though the energy gap could be vanishingly small in the polyacene limit. The bright singlet excited state (1)B2u is a zwitterionic state to the short axis. The excited (1)Ag state gradually switches from a double-excitation state to another zwitterionic state to the short axis, but always keeps its covalent nature to the long axis. An energy crossing between the (1)B2u and excited (1)Ag states happens between hexacene and heptacene. Further energetic consideration suggests that higher acenes are likely to undergo singlet fission with a low photovoltaic efficiency; however, the efficiency might be improved if a singlet fission into multiple triplets could be achieved. PMID:27528690

  3. Nature of ground and electronic excited states of higher acenes.

    PubMed

    Yang, Yang; Davidson, Ernest R; Yang, Weitao

    2016-08-30

    Higher acenes have drawn much attention as promising organic semiconductors with versatile electronic properties. However, the nature of their ground state and electronic excited states is still not fully clear. Their unusual chemical reactivity and instability are the main obstacles for experimental studies, and the potentially prominent diradical character, which might require a multireference description in such large systems, hinders theoretical investigations. Here, we provide a detailed answer with the particle-particle random-phase approximation calculation. The (1)Ag ground states of acenes up to decacene are on the closed-shell side of the diradical continuum, whereas the ground state of undecacene and dodecacene tilts more to the open-shell side with a growing polyradical character. The ground state of all acenes has covalent nature with respect to both short and long axes. The lowest triplet state (3)B2u is always above the singlet ground state even though the energy gap could be vanishingly small in the polyacene limit. The bright singlet excited state (1)B2u is a zwitterionic state to the short axis. The excited (1)Ag state gradually switches from a double-excitation state to another zwitterionic state to the short axis, but always keeps its covalent nature to the long axis. An energy crossing between the (1)B2u and excited (1)Ag states happens between hexacene and heptacene. Further energetic consideration suggests that higher acenes are likely to undergo singlet fission with a low photovoltaic efficiency; however, the efficiency might be improved if a singlet fission into multiple triplets could be achieved.

  4. Charge transfer excitations from excited state Hartree-Fock subsequent minimization scheme

    NASA Astrophysics Data System (ADS)

    Theophilou, Iris; Tassi, M.; Thanos, S.

    2014-04-01

    Photoinduced charge-transfer processes play a key role for novel photovoltaic phenomena and devices. Thus, the development of ab initio methods that allow for an accurate and computationally inexpensive treatment of charge-transfer excitations is a topic that nowadays attracts a lot of scientific attention. In this paper we extend an approach recently introduced for the description of single and double excitations [M. Tassi, I. Theophilou, and S. Thanos, Int. J. Quantum Chem. 113, 690 (2013); M. Tassi, I. Theophilou, and S. Thanos, J. Chem. Phys. 138, 124107 (2013)] to allow for the description of intermolecular charge-transfer excitations. We describe an excitation where an electron is transferred from a donor system to an acceptor one, keeping the excited state orthogonal to the ground state and avoiding variational collapse. These conditions are achieved by decomposing the space spanned by the Hartree-Fock (HF) ground state orbitals into four subspaces: The subspace spanned by the occupied orbitals that are localized in the region of the donor molecule, the corresponding for the acceptor ones and two more subspaces containing the virtual orbitals that are localized in the neighborhood of the donor and the acceptor, respectively. Next, we create a Slater determinant with a hole in the subspace of occupied orbitals of the donor and a particle in the virtual subspace of the acceptor. Subsequently we optimize both the hole and the particle by minimizing the HF energy functional in the corresponding subspaces. Finally, we test our approach by calculating the lowest charge-transfer excitation energies for a set of tetracyanoethylene-hydrocarbon complexes that have been used earlier as a test set for such kind of excitations.

  5. Charge transfer excitations from excited state Hartree-Fock subsequent minimization scheme

    SciTech Connect

    Theophilou, Iris; Tassi, M.; Thanos, S.

    2014-04-28

    Photoinduced charge-transfer processes play a key role for novel photovoltaic phenomena and devices. Thus, the development of ab initio methods that allow for an accurate and computationally inexpensive treatment of charge-transfer excitations is a topic that nowadays attracts a lot of scientific attention. In this paper we extend an approach recently introduced for the description of single and double excitations [M. Tassi, I. Theophilou, and S. Thanos, Int. J. Quantum Chem. 113, 690 (2013); M. Tassi, I. Theophilou, and S. Thanos, J. Chem. Phys. 138, 124107 (2013)] to allow for the description of intermolecular charge-transfer excitations. We describe an excitation where an electron is transferred from a donor system to an acceptor one, keeping the excited state orthogonal to the ground state and avoiding variational collapse. These conditions are achieved by decomposing the space spanned by the Hartree-Fock (HF) ground state orbitals into four subspaces: The subspace spanned by the occupied orbitals that are localized in the region of the donor molecule, the corresponding for the acceptor ones and two more subspaces containing the virtual orbitals that are localized in the neighborhood of the donor and the acceptor, respectively. Next, we create a Slater determinant with a hole in the subspace of occupied orbitals of the donor and a particle in the virtual subspace of the acceptor. Subsequently we optimize both the hole and the particle by minimizing the HF energy functional in the corresponding subspaces. Finally, we test our approach by calculating the lowest charge-transfer excitation energies for a set of tetracyanoethylene-hydrocarbon complexes that have been used earlier as a test set for such kind of excitations.

  6. Super-atom molecular orbital excited states of fullerenes.

    PubMed

    Johansson, J Olof; Bohl, Elvira; Campbell, Eleanor E B

    2016-09-13

    Super-atom molecular orbitals are orbitals that form diffuse hydrogenic excited electronic states of fullerenes with their electron density centred at the centre of the hollow carbon cage and a significant electron density inside the cage. This is a consequence of the high symmetry and hollow structure of the molecules and distinguishes them from typical low-lying molecular Rydberg states. This review summarizes the current experimental and theoretical studies related to these exotic excited electronic states with emphasis on femtosecond photoelectron spectroscopy experiments on gas-phase fullerenes.This article is part of the themed issue 'Fullerenes: past, present and future, celebrating the 30th anniversary of Buckminster Fullerene'.

  7. Lifetime of the Excited State In Vivo

    PubMed Central

    Mar, T.; Govindjee; Singhal, G. S.; Merkelo, H.

    1972-01-01

    Using a mode-locked laser (λ, 632.8 nm), fluorescence decay of chlorophyll (Chl) a in the green alga Chlorella pyrenoidosa, the red alga Porphyridium cruentum, and the blue-green alga Anacystis nidulans was measured by the phase-shift method under conditions when photosynthesis was not operative (3-(3,4-dichlorophenyl)-1,1-dimethylurea [DCMU] poisoning, or cooling to 77°K). In the presence of 10-5 M DCMU, the lifetime of Chl a fluorescence (τ) at room temperature is about 1.7 nsec in Chlorella, 1.0 nsec in Porphyridium, and 0.7 nsec in Anacystis. At 77°K, τ is 1.4 nsec (for fluorescence at about 685 nm, F-685) and 2.3 nsec (for F-730) in Chlorella, 0.9 nsec (F-685) and 1.2 nsec (F-730) in Porphyridium, and 0.8 nsec (F-685 and F-730) in Anacystis. From the above measurement, and the assumption that τ0 (the intrinsic fluorescence lifetime) for Chl a in all three algae is 15.2 nsec, we have calculated the rate constants of radiationless transition (that includes energy transfer to weakly fluorescent system I) processes competing with fluorescence at room temperature to be about 5 × 108 sec-1 in Chlorella, 9 × 108 sec-1 in Porphyridium, and 13 × 108 sec-1 in Anacystis. At 77°K, this rate constant for Chl a that fluoresces at 685 nm remains, in the first approximation, the same as at room temperature. From the τ data, the rate constant for the trapping of excitation energy is calculated to be about 1.2 × 109 sec-1 for Chlorella, 2 × 109 sec-1 for Porphyridium, and 2 × 109 sec-1 for Anacystis. The efficiency of trapping is calculated to be about 66% (Chlorella), 68% (Porphyridium), and 60% (Anacystis). (It is recognized that variations in the above values are to be expected if algae grown under different conditions are used for experimentation.) The maximum quantum yield of Chl a fluorescence for system II (λ, 632.8 nm), calculated from τ measurements, is about 10% in Chlorella, 6-7% in Porhyridium, and 5% in Anacystis under conditions when photosynthesis

  8. Multiscale excited state lifetimes of protonated dimethyl aminopyridines.

    PubMed

    Soorkia, Satchin; Broquier, Michel; Grégoire, Gilles

    2016-09-14

    The excited state dynamics of protonated ortho (2-) and para (4-) dimethyl aminopyridine molecules (DMAPH(+)) has been studied through pump-probe photofragmentation spectroscopy and excited state coupled-cluster CC2 calculations. Multiscale temporal dynamics has been recorded over 9 orders of magnitude from subpicosecond to millisecond. The initially locally excited ππ* state rapidly decays within about 100 fs into a charge transfer state following 90° twist motion of the dimethyl amino group. While this twisted intramolecular charge transfer (TICT) state does not trigger any fragmentation, it selectively leads to specific two-color photofragments through absorption of the probe photon at 355 nm. Besides, the optically dark TICT state provides an efficient deactivation path with high intersystem probability to non-dissociative long-lived triplet states. Such a multiscale pump-probe photodissociation scheme paves the way to systematic studies of charge transfer reactions in the excited state of cold ionic systems stored in a cryogenic cooled ion trap and probed continuously up to the millisecond time scale. PMID:27524459

  9. Multiscale excited state lifetimes of protonated dimethyl aminopyridines.

    PubMed

    Soorkia, Satchin; Broquier, Michel; Grégoire, Gilles

    2016-09-14

    The excited state dynamics of protonated ortho (2-) and para (4-) dimethyl aminopyridine molecules (DMAPH(+)) has been studied through pump-probe photofragmentation spectroscopy and excited state coupled-cluster CC2 calculations. Multiscale temporal dynamics has been recorded over 9 orders of magnitude from subpicosecond to millisecond. The initially locally excited ππ* state rapidly decays within about 100 fs into a charge transfer state following 90° twist motion of the dimethyl amino group. While this twisted intramolecular charge transfer (TICT) state does not trigger any fragmentation, it selectively leads to specific two-color photofragments through absorption of the probe photon at 355 nm. Besides, the optically dark TICT state provides an efficient deactivation path with high intersystem probability to non-dissociative long-lived triplet states. Such a multiscale pump-probe photodissociation scheme paves the way to systematic studies of charge transfer reactions in the excited state of cold ionic systems stored in a cryogenic cooled ion trap and probed continuously up to the millisecond time scale.

  10. Electronic excited states and relaxation dynamics in polymer heterojunction systems

    NASA Astrophysics Data System (ADS)

    Ramon, John Glenn Santos

    The potential for using conducting polymers as the active material in optoelectronic devices has come to fruition in the past few years. Understanding the fundamental photophysics behind their operations points to the significant role played by the polymer interface in their performance. Current device architectures involve the use of bulk heterojunctions which intimately blend the donor and acceptor polymers to significantly increase not only their interfacial surface area but also the probability of exciton formation within the vicinity of the interface. In this dissertation, we detail the role played by the interface on the behavior and performance of bulk heterojunction systems. First, we explore the relation between the exciton binding energy to the band offset in determining device characteristics. As a general rule, when the exciton binding energy is greater than the band offset, the exciton remains the lowest energy excited state leading to efficient light-emitting properties. On the other hand, if the offset is greater than the binding energy, charge separation becomes favorable leading to better photovoltaic behavior. Here, we use a Wannier function, configuration interaction based approach to examine the essential excited states and predict the vibronic absorption and emission spectra of the PPV/BBL, TFB/F8BT and PFB/F8BT heterojunctions. Our results underscore the role of vibrational relaxation in the formation of charge-transfer states following photoexcitation. In addition, we look at the relaxation dynamics that occur upon photoexcitation. For this, we adopt the Marcus-Hush semiclassical method to account for lattice reorganization in the calculation of the interconversion rates in TFB/F8BT and PFB/F8BT. We find that, while a tightly bound charge-transfer state (exciplex) remains the lowest excited state, a regeneration pathway to the optically active lowest excitonic state in TFB/F8BT is possible via thermal repopulation from the exciplex. Finally

  11. Spectroscopy and excited state dynamics of the HNF (DNF) molecule

    NASA Astrophysics Data System (ADS)

    Chen, Jing; Dagdigian, Paul J.

    1992-05-01

    Laser fluorescence excitation has been employed to detect HNF and its isotopomer DNF in the F/HN3(DN3) system. The observation of this molecule in the F+HN3 reaction has confirmed that this reaction proceeds to form HNF+N2, as well as the well-known HF+N3 products. Laser fluorescence excitation scans were taken for a number of HNF and DNF à 2A'(0,v'2,0)-X˜ 2A`(0,0,0) bands. For DNF, excitation of the à (0,2,1) and (0,3,1) levels were also detected. A partial rotational analysis of the DNF bands was carried out. With the derived A rotational constants and previously determined HNF rotational constants, it was possible to derive ground and excited state vibrationally averaged geometries. The K structure of the bands was observed to become simpler with increasing v2, reflecting the reduction in the highest K' levels observable by fluorescence excitation. Decay lifetimes for a variety of HNF and DNF à 2A' excited levels were determined. It was found that the decay rate, scaled approximately by the ν3 factor, increases abruptly at an energy of 23 800±500 cm-1 above the HNF(X˜ 2A`) zero-point level. This threshold is tentatively assigned to the onset of a predissociation channel. The ground and excited states of HNF form a Renner-Teller pair, whose energies become degenerate at linear geometries. The excited state dynamics of HNF (DNF) is compared with the dynamics of the well-studied Renner-Teller molecules HCO and HNO.

  12. Thermal Design of Vapor Cooling of Flight Vehicle Structures Using LH2 Boil-Off

    NASA Technical Reports Server (NTRS)

    Wang, Xiao-Yen; Zoeckler, Joseph

    2015-01-01

    Using hydrogen boil-off vapor to cool the structure of a flight vehicle cryogenic upper stage can reduce heat loads to the stage and increase the usable propellant in the stage or extend the life of the stage. The hydrogen vapor can be used to absorb incoming heat as it increases in temperature before being vented overboard. In theory, the amount of heat leaking into the hydrogen tank from the structure will be reduced if the structure is cooled using the propellant boil-off vapor. However, the amount of boil-off vapor available to be used for cooling and the reduction in heat leak to the propellant tank are dependent to each other. The amount of heat leak reduction to the LH2 tank also depends on the total heat load on the stage and the vapor cooling configurations.

  13. Photoionization of furan from the ground and excited electronic states

    NASA Astrophysics Data System (ADS)

    Ponzi, Aurora; Sapunar, Marin; Angeli, Celestino; Cimiraglia, Renzo; Došlić, Nada; Decleva, Piero

    2016-02-01

    Here we present a comparative computational study of the photoionization of furan from the ground and the two lowest-lying excited electronic states. The study aims to assess the quality of the computational methods currently employed for treating bound and continuum states in photoionization. For the ionization from the ground electronic state, we show that the Dyson orbital approach combined with an accurate solution of the continuum one particle wave functions in a multicenter B-spline basis, at the density functional theory (DFT) level, provides cross sections and asymmetry parameters in excellent agreement with experimental data. On the contrary, when the Dyson orbitals approach is combined with the Coulomb and orthogonalized Coulomb treatments of the continuum, the results are qualitatively different. In excited electronic states, three electronic structure methods, TDDFT, ADC(2), and CASSCF, have been used for the computation of the Dyson orbitals, while the continuum was treated at the B-spline/DFT level. We show that photoionization observables are sensitive probes of the nature of the excited states as well as of the quality of excited state wave functions. This paves the way for applications in more complex situations such as time resolved photoionization spectroscopy.

  14. Photoionization of furan from the ground and excited electronic states.

    PubMed

    Ponzi, Aurora; Sapunar, Marin; Angeli, Celestino; Cimiraglia, Renzo; Došlić, Nađa; Decleva, Piero

    2016-02-28

    Here we present a comparative computational study of the photoionization of furan from the ground and the two lowest-lying excited electronic states. The study aims to assess the quality of the computational methods currently employed for treating bound and continuum states in photoionization. For the ionization from the ground electronic state, we show that the Dyson orbital approach combined with an accurate solution of the continuum one particle wave functions in a multicenter B-spline basis, at the density functional theory (DFT) level, provides cross sections and asymmetry parameters in excellent agreement with experimental data. On the contrary, when the Dyson orbitals approach is combined with the Coulomb and orthogonalized Coulomb treatments of the continuum, the results are qualitatively different. In excited electronic states, three electronic structure methods, TDDFT, ADC(2), and CASSCF, have been used for the computation of the Dyson orbitals, while the continuum was treated at the B-spline/DFT level. We show that photoionization observables are sensitive probes of the nature of the excited states as well as of the quality of excited state wave functions. This paves the way for applications in more complex situations such as time resolved photoionization spectroscopy. PMID:26931702

  15. State-Selective Excitation of Quantum Systems via Geometrical Optimization.

    PubMed

    Chang, Bo Y; Shin, Seokmin; Sola, Ignacio R

    2015-09-01

    We lay out the foundations of a general method of quantum control via geometrical optimization. We apply the method to state-selective population transfer using ultrashort transform-limited pulses between manifolds of levels that may represent, e.g., state-selective transitions in molecules. Assuming that certain states can be prepared, we develop three implementations: (i) preoptimization, which implies engineering the initial state within the ground manifold or electronic state before the pulse is applied; (ii) postoptimization, which implies engineering the final state within the excited manifold or target electronic state, after the pulse; and (iii) double-time optimization, which uses both types of time-ordered manipulations. We apply the schemes to two important dynamical problems: To prepare arbitrary vibrational superposition states on the target electronic state and to select weakly coupled vibrational states. Whereas full population inversion between the electronic states only requires control at initial time in all of the ground vibrational levels, only very specific superposition states can be prepared with high fidelity by either pre- or postoptimization mechanisms. Full state-selective population inversion requires manipulating the vibrational coherences in the ground electronic state before the optical pulse is applied and in the excited electronic state afterward, but not during all times.

  16. Accurate Excited State Geometries within Reduced Subspace TDDFT/TDA.

    PubMed

    Robinson, David

    2014-12-01

    A method for the calculation of TDDFT/TDA excited state geometries within a reduced subspace of Kohn-Sham orbitals has been implemented and tested. Accurate geometries are found for all of the fluorophore-like molecules tested, with at most all valence occupied orbitals and half of the virtual orbitals included but for some molecules even fewer orbitals. Efficiency gains of between 15 and 30% are found for essentially the same level of accuracy as a standard TDDFT/TDA excited state geometry optimization calculation. PMID:26583218

  17. 2{sup +} excitation of the {sup 12}C Hoyle state

    SciTech Connect

    Freer, M.; Fujita, H.; Carter, J.; Usman, I.; Buthelezi, Z.; Foertsch, S. V.; Neveling, R.; Perez, S. M.; Smit, F. D.; Fearick, R. W.; Papka, P.; Swartz, J. A.

    2009-10-15

    A high-energy-resolution magnetic spectrometer has been used to measure the {sup 12}C excitation energy spectrum to search for the 2{sup +} excitation of the 7.65 MeV, 0{sup +} Hoyle state. By measuring in the diffractive minimum of the angular distribution for the broad 0{sup +} background, evidence is found for a possible 2{sup +} state at 9.6(1) MeV with a width of 600(100) keV. The implications for the {sup 8}Be+{sup 4}He reaction rate in stellar environments are discussed.

  18. First-principles Calculation of Excited State Spectra in QCD

    SciTech Connect

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

    2011-05-01

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

  19. Coherent excitation of a single atom to a Rydberg state

    SciTech Connect

    Miroshnychenko, Y.; Gaeetan, A.; Evellin, C.; Grangier, P.; Wilk, T.; Browaeys, A.; Comparat, D.; Pillet, P.

    2010-07-15

    We present the coherent excitation of a single Rubidium atom to the Rydberg state 58d{sub 3/2} using a two-photon transition. The experimental setup is described in detail, as are experimental techniques and procedures. The coherence of the excitation is revealed by observing Rabi oscillations between ground and Rydberg states of the atom. We analyze the observed oscillations in detail and compare them to numerical simulations which include imperfections of our experimental system. Strategies for future improvements on the coherent manipulation of a single atom in our settings are given.

  20. Formation of metastable excited states during sputtering of transition metals

    SciTech Connect

    Wucher, A.; Sroubek, Z.

    1997-01-01

    We propose a simple model which treats the formation of metastable excited neutral atoms during sputtering of a transition metal as a two step process. First, the energy deposited into the electronic system of the solid by electronic energy losses of all moving particles in the collision cascade is considered to lead to a locally altered equilibrium electronic state of the solid. It is found that this step is dominated by collective interaction with the conduction band electrons rather than by electron promotion in binary atom-atom collisions. Second, sputtered excited atoms are assumed to be formed by resonant neutralization of excited ions (reflecting the altered equilibrium state) while crossing the surface. It is shown that this model explains the total as well as the velocity dependent excitation probability observed in recent experiments on sputtered neutral silver atoms, which cannot be understood in terms of existing theories describing the formation of excited states in sputtering. {copyright} {ital 1996} {ital The American Physical Society}

  1. Formation of ground and excited states of antihydrogen

    SciTech Connect

    Nahar, S.N.; Wadehra, J.M.

    1988-06-01

    Differential and integrated cross sections for the formation of antihydrogen by the impact of intermediate-energy (20--500 keV) antiprotons on positronium are calculated using the first Born approximation. The calculations are carried out for the formation of antihydrogen in ground and various excited electronic states (n = 1--3) when positronium, the target atom, is in the ground state, and for the formation of antihydrogen in the ground state when the positronium is in various excited electronic states (n = 1--2). The 1/n/sup 3/ behavior for the capture cross sections is used to calculate the total (that is, all states added together) integrated cross sections. The cross sections for the formation of antihydrogen presented here are obtained from those for the formation of positronium by the impact of positrons on hydrogen atoms by using charge invariance and the principle of detailed balance.

  2. Crystallization and preliminary X-ray diffraction analysis of the peripheral light-harvesting complex LH2 from Marichromatium purpuratum.

    PubMed

    Cranston, Laura J; Roszak, Aleksander W; Cogdell, Richard J

    2014-06-01

    LH2 from the purple photosynthetic bacterium Marichromatium (formerly known as Chromatium) purpuratum is an integral membrane pigment-protein complex that is involved in harvesting light energy and transferring it to the LH1-RC `core' complex. The purified LH2 complex was crystallized using the sitting-drop vapour-diffusion method at 294 K. The crystals diffracted to a resolution of 6 Å using synchrotron radiation and belonged to the tetragonal space group I4, with unit-cell parameters a=b=109.36, c=80.45 Å. The data appeared to be twinned, producing apparent diffraction symmetry I422. The tetragonal symmetry of the unit cell and diffraction for the crystals of the LH2 complex from this species reveal that this complex is an octamer.

  3. Crystallization and preliminary X-ray diffraction analysis of the peripheral light-harvesting complex LH2 from Marichromatium purpuratum

    PubMed Central

    Cranston, Laura J.; Roszak, Aleksander W.; Cogdell, Richard J.

    2014-01-01

    LH2 from the purple photosynthetic bacterium Marichromatium (formerly known as Chromatium) purpuratum is an integral membrane pigment–protein complex that is involved in harvesting light energy and transferring it to the LH1–RC ‘core’ complex. The purified LH2 complex was crystallized using the sitting-drop vapour-diffusion method at 294 K. The crystals diffracted to a resolution of 6 Å using synchrotron radiation and belonged to the tetragonal space group I4, with unit-cell parameters a = b = 109.36, c = 80.45 Å. The data appeared to be twinned, producing apparent diffraction symmetry I422. The tetragonal symmetry of the unit cell and diffraction for the crystals of the LH2 complex from this species reveal that this complex is an octamer. PMID:24915099

  4. Tuning ground states and excitations in complex electronic materials

    SciTech Connect

    Bishop, A.R.

    1996-09-01

    Modern electronic materials are characterized by a great variety of broken-symmetry ground states and excitations. Their control requires understanding and tuning underlying driving forces of spin-charge-lattice coupling, critical to macroscopic properties and applications. We report representative model calculations which demonstrate some of the richness of the phenomena and the challenges for successful microscopic modeling.

  5. Suppression of excited-state absorption in laser crystals

    NASA Astrophysics Data System (ADS)

    Kuznetsova, Elena; Kolesov, Roman; Kocharovskaya, Olga

    2004-10-01

    Currently, a lot of experimental effort in solid-state optics is devoted to searching for laser materials suitable for tunable lasing, primarily in UV and VUV spectral regions. Researchers mainly focus on optical crystals doped with either transition metal or rare-earth ions. The latter ones doped into wide bandgap dielectric crystals have spectrally broad vibronic emission bands associated with 4fn-15d â" 4fn interconfigurational transitions, whose energies lie mostly in UV and VUV regions of the spectrum. The transitions are electric-dipole-allowed, therefore have large absorption and emission cross-sections, and are promising for efficient tunable laser action. However, in almost all promising crystals laser action in UV and VUV is hindered or completely prohibited due to excited-state absorption (ESA), i.e. absorption from metastable laser levels to higher-energy states, which occurs at emission or/and pump wavelengths. A method of suppression of losses due to excited-state absorption (ESA) in laser crystals is proposed, based on a well-known phenomenon of electromagnetically induced transparency (EIT). Absorption from a populated excited electronic state can be reduced under the action of an additional driving coherent field, resonantly coupling the terminal state of ESA to some intermediate discrete state.

  6. Two-Photon Excitation of trans-Stilbene: Spectroscopy and Dynamics of Electronically Excited States above S1.

    PubMed

    Houk, Amanda L; Zheldakov, Igor L; Tommey, Tyler A; Elles, Christopher G

    2015-07-23

    The photoisomerization dynamics of trans-stilbene have been well studied in the lowest excited state, but much less is known about the behavior following excitation to higher-lying electronically excited states. This contribution reports a combined study of the spectroscopy and dynamics of two-photon accessible states above S1. Two-photon absorption (2PA) measurements using a broadband pump-probe technique reveal distinct bands near 5.1 and 6.4 eV. The 2PA bands have absolute cross sections of 40 ± 16 and 270 ± 110 GM, respectively, and a pump-probe polarization dependence that suggests both of the transitions access Ag-symmetry excited states. Separate transient absorption measurements probe the excited-state dynamics following two-photon excitation into each of the bands using intense pulses of 475 and 380 nm light, respectively. The initially excited states rapidly relax via internal conversion, leading to the formation of an S1 excited-state absorption band that is centered near 585 nm and evolves on a time scale of 1-2 ps due to intramolecular vibrational relaxation. The subsequent evolution of the S1 excited-state absorption is identical to the behavior following direct one-photon excitation of the lowest excited state at 4.0 eV. The complementary spectroscopy and dynamics measurements provide new benchmarks for computational studies of the electronic structure and dynamics of this model system on excited states above S1. Probing the dynamics of molecules in their higher-lying excited states is an important frontier in chemical reaction dynamics.

  7. Excited state nucleon spectrum with two flavors of dynamical fermions

    SciTech Connect

    Bulava, John M.; Foley, Justin; Morningstar, Colin; Edwards, Robert G.; Joo, Balint; Lin, Huey-Wen; Richards, David G.; Engelson, Eric; Wallace, Stephen J.; Lichtl, Adam; Mathur, Nilmani

    2009-02-01

    Highly excited states for isospin (1/2) baryons are calculated for the first time using lattice QCD with two flavors of dynamical quarks. Anisotropic lattices are used with two pion masses, m{sub {pi}}=416(36) MeV and 578(29) MeV. The lowest four energies are reported in each of the six irreducible representations of the octahedral group at each pion mass. The lattices used have dimensions 24{sup 3}x64, spatial lattice spacing a{sub s}{approx_equal}0.11 fm, and temporal lattice spacing a{sub t}=(1/3)a{sub s}. Clear evidence is found for a (5{sup -}/2) state in the pattern of negative-parity excited states. This agrees with the pattern of physical states and spin (5/2) has been realized for the first time on the lattice.

  8. Lattice QCD determination of patterns of excited baryon states

    SciTech Connect

    Basak, Subhasish; Edwards, R. G.; Richards, D. G.; Fleming, G. T.; Juge, K. J.; Lichtl, A.; Morningstar, C.; Sato, I.; Wallace, S. J.

    2007-10-01

    Energies for excited isospin I=(1/2) and I=(3/2) states that include the nucleon and {delta} families of baryons are computed using quenched, anisotropic lattices. Baryon interpolating field operators that are used include nonlocal operators that provide G{sub 2} irreducible representations of the octahedral group. The decomposition of spin (5/2) or higher spin states is realized for the first time in a lattice QCD calculation. We observe patterns of degenerate energies in the irreducible representations of the octahedral group that correspond to the subduction of the continuum spin (5/2) or higher. The overall pattern of low-lying excited states corresponds well to the pattern of physical states subduced to the irreducible representations of the octahedral group.

  9. Lattice QCD determination of patterns of excited baryon states

    SciTech Connect

    Subhasish Basak; Robert Edwards; George Fleming; Keisuke Juge; Adam Lichtl; Colin Morningstar; David Richards; Ikuro Sato; Stephen Wallace

    2007-10-01

    Energies for excited isospin I = 1/2 and I = 3/2 states that include the nucleon and Delta families of baryons are computed using quenched, anisotropic lattices. Baryon interpolating field operators that are used include nonlocal operators that provide G2 irreducible representations of the octahedral group. The decomposition of spin 5/2 or higher spin states is realized for the first time in a lattice QCD calculation. We observe patterns of degenerate energies in the irreducible representations of the octahedral group that correspond to the subduction of the continuum spin 5/2 or higher. The overall pattern of low-lying excited states corresponds well to the pattern of physical states subduced to the irreducible representations of the octahedral group.

  10. Excited-state quantum phase transition in the Rabi model

    NASA Astrophysics Data System (ADS)

    Puebla, Ricardo; Hwang, Myung-Joong; Plenio, Martin B.

    2016-08-01

    The Rabi model, a two-level atom coupled to a harmonic oscillator, can undergo a second-order quantum phase transition (QPT) [M.-J. Hwang et al., Phys. Rev. Lett. 115, 180404 (2015), 10.1103/PhysRevLett.115.180404]. Here we show that the Rabi QPT accompanies critical behavior in the higher-energy excited states, i.e., the excited-state QPT (ESQPT). We derive analytic expressions for the semiclassical density of states, which show a logarithmic divergence at a critical energy eigenvalue in the broken symmetry (superradiant) phase. Moreover, we find that the logarithmic singularities in the density of states lead to singularities in the relevant observables in the system such as photon number and atomic polarization. We corroborate our analytical semiclassical prediction of the ESQPT in the Rabi model with its numerically exact quantum mechanical solution.

  11. Exotic nucleus helium 9 and its excited states

    SciTech Connect

    Seth, K.K.; Artuso, M.; Barlow, D.; Iversen, S.; Kaletka, M.; Nann, H.; Parker, B.; Soundranayagam, R.

    1987-05-11

    The ground state and several excited states of /sup 9/He, the most neutron-rich nucleus to date, have been identified by means of the reaction /sup 9/Be(..pi../sup -/,..pi../sup +/) /sup 9/He. The mass excess of the ground state has been measured and it is found that the nucleus is unbound against single-neutron decay by 1.13 +- 0.10 MeV only. It is found that the excited-state spectrum of this nucleus, which is very far from the valley of stability, is in good agreement with the predictions of ''no-core'' shell-model calculations whose parameters were optimized for the stable nuclei in the valley.

  12. Excited state cross sections for Er-doped glasses

    NASA Astrophysics Data System (ADS)

    Zemon, Stanley A.; Lambert, Gary M.; Miniscalco, William J.; Davies, Richard W.; Hall, Bruce T.; Folweiler, Robert C.; Wei, Ta-Sheng; Andrews, Leonard J.; Singh, Mahendra P.

    1991-01-01

    Excited-state-absorption (ESA) cross sections were determined for the region between 760 and 900 nm for Er-doped fluorophosphate phosphate and silicate glasses. Measurements were performed on multimode fibers pumping at 647 nm with powers 1 . 5 Wto invert the population into the saturation regime. Over much of the 800-nm band ground-state-absorption (GSA) cross sections are equal to or greater than ESA cross sections. For comparison ESA was also measured for singlemode Al/P-doped silica fiber. The cross sections were incorporated into an amplifier model and the phosphate and fluorophosphate glasses were found to provide higher gain than silica for pumping in the 800-nm band. Photoexcited fluorozirconates were found to have substantial populations in the first four excited states and ESA transitions originating from these states are identified.

  13. Direct excitation of butterfly states in Rydberg molecules

    NASA Astrophysics Data System (ADS)

    Lippe, Carsten; Niederpruem, Thomas; Thomas, Oliver; Eichert, Tanita; Ott, Herwig

    2016-05-01

    Since their first theoretical prediction Rydberg molecules have become an increasing field of research. These exotic states originate from the binding of a ground state atom in the electronic wave function of a highly-excited Rydberg atom mediated by a Fermi contact type interaction. A special class of long-range molecular states, the butterfly states, were first proposed by Greene et al.. These states arise from a shape resonance in the p-wave scattering channel of a ground state atom and a Rydberg electron and are characterized by an electron wavefunction whose density distribution resembles the shape of a butterfly. We report on the direct observation of deeply bound butterfly states of Rydberg molecules of 87 Rb. The butterfly states are studied by high resolution spectroscopy of UV-excited Rydberg molecules. We find states bound up to - 50 GHz from the 25 P1/2 , F = 1 state, corresponding to binding lengths of 50a0 to 500a0 and with permanent electric dipole moments of up to 500 Debye. This distinguishes the observed butterfly states from the previously observed long range Rydberg molecules in rubidium.

  14. Ultrafast excited-state dynamics of copper(I) complexes.

    PubMed

    Iwamura, Munetaka; Takeuchi, Satoshi; Tahara, Tahei

    2015-03-17

    Bis-diimine Cu(I) complexes exhibit strong absorption in the visible region owing to the metal-to-ligand charge transfer (MLCT) transitions, and the triplet MLCT ((3)MLCT) states have long lifetimes. Because these characteristics are highly suitable for photosensitizers and photocatalysts, bis-diimine Cu(I) complexes have been attracting much interest. An intriguing feature of the Cu(I) complexes is the photoinduced structural change called "flattening". Bis-diimine Cu(I) complexes usually have tetrahedron-like D2d structures in the ground (S0) state, in which two ligands are perpendicularly attached to the Cu(I) ion. With MLCT excitation, the central Cu(I) ion is formally oxidized to Cu(II), which induces the structural change to the "flattened" square-planar-like structure that is seen for usual Cu(II) complexes. In this Account, we review our recent studies on ultrafast excited-state dynamics of bis-diimine Cu(I) complexes carried out using femtosecond time-resolved optical spectroscopy. Focusing on three prototypical bis-diimine Cu(I) complexes that have 1,10-phenanthroline ligands with different substituents at the 2,9-positions, i.e., [Cu(phen)2](+) (phen = 1,10-phenanthroline), [Cu(dmphen)2](+) (dmphen = 2,9-dimethyl-1,10-phenanthroline), and [Cu(dpphen)2](+) (dpphen = 2,9-diphenyl-1,10-phenanthroline), we examined their excited-state dynamics by time-resolved emission and absorption spectroscopies with 200 fs time resolution, observed the excited-state coherent nuclear motion with 30 fs time resolution and performed complementary theoretical calculations. This combined approach vividly visualizes excited-state processes in the MLCT state of bis-diimine Cu(I) complexes. It was demonstrated that flattening distortion, internal conversion, and intersystem crossing occur on the femtosecond-early picosecond time scale, and their dynamics is clearly identified separately. The flattening distortion predominantly occurs in the S1 state on the subpicosecond time

  15. Excited States of the Diatomic Molecule CrHe

    NASA Astrophysics Data System (ADS)

    Pototschnig, Johann V.; Ratschek, Martin; Hauser, Andreas W.; Ernst, Wolfgang E.

    2013-06-01

    Chromium (Cr) atoms embedded in superfluid helium nanodroplets (He_N) have been investigated by laser induced fluorescence, beam depletion and resonant two-photon ionization spectroscopy in current experiments at our institute. Cr is found to reside inside the He_N in the a^7S ground state. Two electronically excited states, z^7P and y^7P, are involved in a photoinduced ejection process which allowed us to study Fano resonances in the photoionisation spectra The need for a better understanding of the experimental observations triggered a theoretical approach towards the computation of electronically excited states via high-level methods of computational chemistry. Two well-established, wave function-based methods, CASSCF and MRCI, are combined to calculate the potential energy curves for the three states involved. The character of the two excited states z^7P and y^7P turns out to be significantly different. Theory predicts the ejection of the Cr atom in the case of an y^7P excitation as was observed experimentally. The quasi-inert helium environment is expected to weaken spin selection rules, allowing a coupling between different spin states especially during the ejection process. We therefore extend our theoretical analysis to the lowest state in the triplet- and quintet- manifold. Most of these alternative states show very weak bonding of only a few wn. A. Kautsch, M. Hasewend, M. Koch and W. E. Ernst, Phys. Rev. A 86, 033428 (2012). A. Kautsch, M. Koch and W. E. Ernst, J. Phys. Chem. A, accepted, doi:10.1021/jp312336m}.

  16. Doubly Excited Resonance States of Helium Atom: Complex Entropies

    NASA Astrophysics Data System (ADS)

    Kuroś, Arkadiusz; Kościk, Przemysław; Saha, Jayanta K.

    2016-09-01

    We provide a diagonal form of a reduced density matrix of S-symmetry resonance states of two electron systems determined under the framework of the complex scaling method. We have employed the variational Hylleraas type wavefunction to estimate the complex entropies in doubly excited resonance states of helium atom. Our results are in good agreement with the corresponding ones determined under the framework of the stabilization method (Lin and Ho in Few-Body Syst 56:157, 2015).

  17. Integrating proton coupled electron transfer (PCET) and excited states

    SciTech Connect

    Gagliardi, Christopher J.; Westlake, Brittany C.; Kent, Caleb A.; Paul, Jared J.; Papanikolas, John M.; Meyer, Thomas J.

    2010-11-01

    In many of the chemical steps in photosynthesis and artificial photosynthesis, proton coupled electron transfer (PCET) plays an essential role. An important issue is how excited state reactivity can be integrated with PCET to carry out solar fuel reactions such as water splitting into hydrogen and oxygen or water reduction of CO2 to methanol or hydrocarbons. The principles behind PCET and concerted electron–proton transfer (EPT) pathways are reasonably well understood. In Photosystem II antenna light absorption is followed by sensitization of chlorophyll P680 and electron transfer quenching to give P680+. The oxidized chlorophyll activates the oxygen evolving complex (OEC), a CaMn4 cluster, through an intervening tyrosine–histidine pair, YZ. EPT plays a major role in a series of four activation steps that ultimately result in loss of 4e-/4H+ from the OEC with oxygen evolution. The key elements in photosynthesis and artificial photosynthesis – light absorption, excited state energy and electron transfer, electron transfer activation of multiple-electron, multiple-proton catalysis – can also be assembled in dye sensitized photoelectrochemical synthesis cells (DS-PEC). In this approach, molecular or nanoscale assemblies are incorporated at separate electrodes for coupled, light driven oxidation and reduction. Separate excited state electron transfer followed by proton transfer can be combined in single semi-concerted steps (photo-EPT) by photolysis of organic charge transfer excited states with H-bonded bases or in metal-to-ligand charge transfer (MLCT) excited states in pre-associated assemblies with H-bonded electron transfer donors or acceptors. In these assemblies, photochemically induced electron and proton transfer occur in a single, semi-concerted event to give high-energy, redox active intermediates.

  18. Excited-state collisions of trapped 85Rb atoms

    NASA Astrophysics Data System (ADS)

    Hoffmann, D.; Feng, P.; Williamson, R. S., III; Walker, T.

    1992-08-01

    We descrbe a new method for measuring excited-state collisions between optically trapped atoms. With this method, trap-loss collision rates are deduced from the loading behavior of clouds of trapped atoms in the regime where radiation trapping limits the atom density. Our measurements indicate that 85Rb trap-loss collisions occur at significantly smaller rates than expected both from previous work on Cs and from recent models. In addition, the dependence of the trap-loss collisions on the frequency of the light used to excite the atom pairs is also different from that of Cs, suggesting that assumptions about the dynamics in these models need modification.

  19. Photodissociation of N2O: excitation of 1A" states.

    PubMed

    Schinke, Reinhard; Schmidt, Johan A

    2012-11-26

    We investigate the contributions of the lowest two (1)A" states in the UV photodissociation of N(2)O employing three-dimensional potential energy surfaces and transition dipole moment functions. Because the transition dipole moments are much smaller than for the 2 (1)A' state, we conclude that excitation of the (1)A" states has a marginal effect. The dense vibrational spectrum of the quasi-bound 2(1)A" state possibly explains some of the tiny, noise-like structures of the measured absorption spectrum. PMID:22536943

  20. Excited S-symmetry states of positronic lithium and beryllium

    NASA Astrophysics Data System (ADS)

    Strasburger, Krzysztof

    2016-04-01

    The possibility of the existence of excited S-symmetry states of positronic lithium and beryllium, resulting from the positron attachment to high-spin P parent atomic states, is examined and confirmed with variational calculations in the basis of explicitly correlated Gaussian functions. The unexpectedly different order of the energies of the S and P states is explained by the formation of the positronium cluster structure and associated disappearance of the destabilizing centrifugal force. The annihilation properties of newly discovered states are discussed in the context of prospective experimental detection.

  1. Excited S-symmetry states of positronic lithium and beryllium.

    PubMed

    Strasburger, Krzysztof

    2016-04-14

    The possibility of the existence of excited S-symmetry states of positronic lithium and beryllium, resulting from the positron attachment to high-spin P parent atomic states, is examined and confirmed with variational calculations in the basis of explicitly correlated Gaussian functions. The unexpectedly different order of the energies of the S and P states is explained by the formation of the positronium cluster structure and associated disappearance of the destabilizing centrifugal force. The annihilation properties of newly discovered states are discussed in the context of prospective experimental detection. PMID:27083730

  2. Intramolecular energy transfer and excitation coupling in metal-to-ligand charge transfer (MLCT) excited states

    NASA Astrophysics Data System (ADS)

    Riesen, Hans; Krausz, Elmars

    1995-02-01

    Several new spectroscopic studies relating to the coupling and dynamics in the spin-forbidden 3MLCT excited states of the chromophores [Ru(bpy)3]2+ and [Os(bpy)3]2+ (bpy equals 2,2'-bipyridine) in the racemic crystal lattices [Ru(bpy)3](PF6)2, [Ru(bpy)3](ClO4)2 and [Zn(bpy)3](ClO4)2 are presented. In the first of these lattices there are three closely related chromophoric sites at low temperatures, each with trigonal (C3) symmetry. In the two, isomorphic perchlorate salts there is a single chromophoric site, which has C2 symmetry. Using time resolved luminescence line narrowing, we have been able to directly measure the excitation transfer rate between two equivalent metal-ligand units in the [Ru(bpy)3]2+ chromophore doped in the [Zn(bpy)3](ClO4)2 lattice. The rate obtained (approximately equals 1 X 108 sec-1) is in excellent accord with estimates made from the observed linewidth in Stark swept transient hole-burning experiments made on the same system and confirm the single ligand, localized nature of the lowest emitting excited states and thus the very weak intramolecular coupling between metal ligand sub-units within this chromophore. The corresponding coupling in the [Os(bpy)3]2+ system is stronger and, in contrast to the ruthenium analogue, gives rise to additional features in the optical spectra in the origin region of the lowest 3MLCT excited states. The magnitude of the coupling can be probed and assessed by preparing modified chromophoric materials, in which one or two of the bpy ligands are perdeuterated (bpy-d8). This selective deuteration breaks the (near) degeneracy of excitations involving crystallographically equivalent ligands by approximately equals 30 - 40 cm-1 and this competes with or completely overrides the exciton coupling process. The exciton coupling is found to be approximately equals 2.4 cm-1 for [Os(bpy)3]2+ doped in [Ru(bpy)3](PF6)2 and can be understood within a mini-exciton description. Stronger couplings for the same chromophore in

  3. Description of electronic excited states using electron correlation operator.

    PubMed

    Nichols, Bryan; Rassolov, Vitaly A

    2013-09-14

    The electron correlation energy in a chemical system is defined as a difference between the energy of an exact energy for a given Hamiltonian, and a mean-field, or single determinant, approximation to it. A promising way to model electron correlation is through the expectation value of a linear two-electron operator for the Kohn-Sham single determinant wavefunction. For practical reasons, it is desirable for such an operator to be universal, i.e., independent of the positions and types of nuclei in a molecule. The correlation operator models the effect of electron correlation on the interaction energy in a electron pair. We choose an operator expanded in a small number of Gaussians as a model for electron correlation, and test it by computing atomic and molecular adiabatic excited states. The computations are performed within the Δ Self-Consistent Field (ΔSCF) formalism, and are compared to the time-dependent density functional theory model with popular density functionals. The simplest form of the correlation operator contains only one parameter derived from the helium atom ground state correlation energy. The correlation operator approach significantly outperforms other methods in computation of atomic excitation energies. The accuracy of molecular excitation energies computed with the correlation operator is limited by the shortcomings of the ΔSCF methodology in describing excited states.

  4. Link atom bond length effect in ONIOM excited state calculations.

    PubMed

    Caricato, Marco; Vreven, Thom; Trucks, Gary W; Frisch, Michael J

    2010-08-01

    We investigate how the choice of the link atom bond length affects an electronic transition energy calculation with the so-called our own N-layer integrated molecular orbital molecular mechanics (ONIOM) hybrid method. This follows our previous paper [M. Caricato et al., J. Chem. Phys. 131, 134105 (2009)], where we showed that ONIOM is able to accurately approximate electronic transition energies computed at a high level of theory such as the equation of motion coupled cluster singles and doubles (EOM-CCSD) method. In this study we show that the same guidelines used in ONIOM ground state calculations can also be followed in excited state calculations, and that the link atom bond length has little effect on the ONIOM energy when a sensible model system is chosen. We also suggest further guidelines for excited state calculations which can help in checking the effectiveness of the definition of the model system and controlling the noise in the calculation.

  5. Characterising a configuration interaction excited state using natural transition geminals

    NASA Astrophysics Data System (ADS)

    Coe, J. P.; Paterson, M. J.

    2014-03-01

    We introduce natural transition geminals as a means to qualitatively understand a transition where double excitations are important. The first two A1 singlet states of the CH cation are used as an initial example. We calculate these states with configuration interaction singles and state-averaged Monte Carlo configuration interaction (SA-MCCI). For each method, we compare the important natural transition geminals with the dominant natural transition orbitals. We then compare SA-MCCI and full configuration interaction with regards to the natural transition geminals using the beryllium atom. We compare using the natural transition geminals with analysing the important configurations in the CI expansion to give the dominant transition for the beryllium atom and the carbon dimer. Finally, we calculate the natural transition geminals for two electronic excitations of formamide.

  6. Controlling excited-state contamination in nucleon matrix elements

    NASA Astrophysics Data System (ADS)

    Yoon, Boram; Gupta, Rajan; Bhattacharya, Tanmoy; Engelhardt, Michael; Green, Jeremy; Joó, Bálint; Lin, Huey-Wen; Negele, John; Orginos, Kostas; Pochinsky, Andrew; Richards, David; Syritsyn, Sergey; Winter, Frank; Nucleon Matrix Elements NME Collaboration

    2016-06-01

    We present a detailed analysis of methods to reduce statistical errors and excited-state contamination in the calculation of matrix elements of quark bilinear operators in nucleon states. All the calculations were done on a 2 +1 -flavor ensemble with lattices of size 323×64 generated using the rational hybrid Monte Carlo algorithm at a =0.081 fm and with Mπ=312 MeV . The statistical precision of the data is improved using the all-mode-averaging method. We compare two methods for reducing excited-state contamination: a variational analysis and a 2-state fit to data at multiple values of the source-sink separation tsep. We show that both methods can be tuned to significantly reduce excited-state contamination and discuss their relative advantages and cost effectiveness. A detailed analysis of the size of source smearing used in the calculation of quark propagators and the range of values of tsep needed to demonstrate convergence of the isovector charges of the nucleon to the tsep→∞ estimates is presented.

  7. Embedding potentials for excited states of embedded species

    SciTech Connect

    Wesolowski, Tomasz A.

    2014-05-14

    Frozen-Density-Embedding Theory (FDET) is a formalism to obtain the upper bound of the ground-state energy of the total system and the corresponding embedded wavefunction by means of Euler-Lagrange equations [T. A. Wesolowski, Phys. Rev. A 77(1), 012504 (2008)]. FDET provides the expression for the embedding potential as a functional of the electron density of the embedded species, electron density of the environment, and the field generated by other charges in the environment. Under certain conditions, FDET leads to the exact ground-state energy and density of the whole system. Following Perdew-Levy theorem on stationary states of the ground-state energy functional, the other-than-ground-state stationary states of the FDET energy functional correspond to excited states. In the present work, we analyze such use of other-than-ground-state embedded wavefunctions obtained in practical calculations, i.e., when the FDET embedding potential is approximated. Three computational approaches based on FDET, that assure self-consistent excitation energy and embedded wavefunction dealing with the issue of orthogonality of embedded wavefunctions for different states in a different manner, are proposed and discussed.

  8. Reexamination of the excited states of C12

    NASA Astrophysics Data System (ADS)

    Freer, M.; Boztosun, I.; Bremner, C. A.; Chappell, S. P. G.; Cowin, R. L.; Dillon, G. K.; Fulton, B. R.; Greenhalgh, B. J.; Munoz-Britton, T.; Nicoli, M. P.; Rae, W. D. M.; Singer, S. M.; Sparks, N.; Watson, D. L.; Weisser, D. C.

    2007-09-01

    An analysis of the C12(C12,3α)C12 reaction was made at beam energies between 82 and 106 MeV. Decays to both the ground state and the excited states of Be8 were isolated, allowing states of different characters to be identified. In particular, evidence was found for a previously observed state at 11.16 MeV. An analysis of the angular distributions of the unnatural parity states at 11.83 and 13.35 MeV, previously assigned Jπ=2-, calls into question the validity of these assignments, suggesting that at least one of the states may correspond to Jπ=4-. Evidence is also found for 1- and 3- strengths associated with broad states between 11 and 14 MeV.

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

    NASA Astrophysics Data System (ADS)

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

    2011-02-01

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

  10. Negative-parity nucleon excited state in nuclear matter

    NASA Astrophysics Data System (ADS)

    Ohtani, Keisuke; Gubler, Philipp; Oka, Makoto

    2016-10-01

    Spectral functions of the nucleon and its negative-parity excited state in nuclear matter are studied by using QCD sum rules and the maximum entropy method (MEM). It is found that in-medium modifications of the spectral functions are attributed mainly to density dependencies of the and condensates. The MEM reproduces the lowest-energy peaks of both the positive- and negative-parity nucleon states at finite density up to ρ ˜ρN (normal nuclear matter density). As the density grows, the residue of the nucleon ground state decreases gradually while the residue of the lowest negative-parity excited state increases slightly. On the other hand, the positions of the peaks, which correspond to the total energies of these states, are almost density independent for both parity states. The density dependencies of the effective masses and vector self-energies are also extracted by assuming phenomenological mean-field-type propagators for the peak states. We find that, as the density increases, the nucleon effective mass decreases while the vector self-energy increases. The density dependence of these quantities for the negative-parity state on the other hand turns out to be relatively weak.

  11. Excitation on the Coherent States of Pseudoharmonic Oscillator

    SciTech Connect

    Popov, Dusan; Pop, Nicolina; Sajfert, Vjekoslav

    2009-05-22

    In the last decades, much attention has been paid to the excitation on coherent states, especially for coherent states of the harmonic oscillator ([1] and references therein). But an interesting anharmonic oscillator with many potential applications is also the pseudoharmonic oscillator (PHO). So, in the present paper we have defined the excitation on the Klauder-Perelomov coherent states (E-KP-CSs) for the PHO. These states are obtained by repeatedly operating the raising operator K{sub +} on a usual Klauder-Perelomov coherent state (KP-CS) of the PHO [2]. We have verified that really, the E-KP-CSs fulfill all the properties of the coherent states, as stated by Klauder [3]. We have examined the nonclassical properties of the E-KP-CSs, by using the density matrix formalism and examining the dependence of the Mandel parameter Q{sub z,k;m}(|z|{sup 2}) on the |z|{sup 2} and on the m. It seems that these states can be used in optical communication field and in the physics of quantum information, as signal beams, due to the fact that in these fields the nonclassicality plays an important role.

  12. Recent Advances in LOX / LH2 Propulsion System for Reusable Vehicle Testing

    NASA Astrophysics Data System (ADS)

    Tokudome, Shinichiro; Naruo, Yoshihiro; Yagishita, Tsuyoshi; Nonaka, Satoshi; Shida, Maki; Mori, Hatsuo; Nakamura, Takeshi

    The third-generation vehicle RVT#3 equipped with a pressure-fed engine, which had upgraded in terms of durability enhancement and a LH2 tank of composite material, successfully performed in repeated flight operation tests; and the vehicle reached its maximum flying altitude of 42m in October 2003. The next step for demonstrating entire sequence of full-scale operation is to put a turbopump-fed system into propulsion system. From a result of primary system analysis, we decided to build an expander-cycle engine by diverting a pair of turbopumps, which had built for another research program, to the present study. A combustion chamber with long cylindrical portion adapted to the engine cycle was also newly made. Two captive firing tests have been conducted with two different thrust control methods, following the component tests of combustor and turbopumps separately conducted. A considerable technical issues recognized in the tests were the robustness enhancement of shaft seal design, the adjustment of shaft stiffness, and start-up operation adapted to the specific engine system. Experimental study of GOX/GH2 RCS thrusters have also been started as a part of a conceptual study of the integration of the propulsion system associated with simplification and reliability improvement of the vehicle system.

  13. Higher excited states of acceptors in cubic semiconductors

    NASA Astrophysics Data System (ADS)

    Said, M.; Kanehisa, M. A.; Balkanski, M.

    1986-02-01

    For the first time, higher excited states of shallow acceptors up to the 3s and 4s states are calculated based on the Balderschi and Lipari theory including the cubic correction. The eigenvalues and eigenvectors of the effective mass Hamiltonian for shallow acceptor states were obtained by the finite element method. The resultant sparse matrix is diagonalized by a newly developed Saad's method based on Arnoldi's algorithm. Comparison with experimental spectra on ZnTe:Li and ZnTe:P gives best valence band parameters for ZnTe; μ = 0.60 and δ = 0.12.

  14. Excited-state quantum phase transitions in Dicke superradiance models.

    PubMed

    Brandes, Tobias

    2013-09-01

    We derive analytical results for various quantities related to the excited-state quantum phase transitions in a class of Dicke superradiance models in the semiclassical limit. Based on a calculation of a partition sum restricted to Dicke states, we discuss the singular behavior of the derivative of the density of states and find observables such as the mean (atomic) inversion and the boson (photon) number and its fluctuations at arbitrary energies. Criticality depends on energy and a parameter that quantifies the relative weight of rotating versus counterrotating terms, and we find a close analogy to the logarithmic and jump-type nonanalyticities known from the Lipkin-Meshkov-Glick model. PMID:24125239

  15. Strong-Field Photoionization as Excited-State Tunneling.

    PubMed

    Serebryannikov, E E; Zheltikov, A M

    2016-03-25

    We show that, in an intense laser field, ultrafast photoionization can occur through quantum pathways that cannot be categorized as multiphoton ionization or ground-state tunneling. In this regime, the subcycle electron-wave-packet dynamics leading to photoionization occurs via electron excited states, from where the electrons tunnel to the continuum within a tiny fraction of the field cycle. For high field intensities, this ionization pathway is shown to drastically enhance the dynamic leakage of the electron wave packet into the continuum, opening an ionization channel that dominates over ground-state electron tunneling. PMID:27058079

  16. Signature of nonadiabatic coupling in excited-state vibrational modes.

    PubMed

    Soler, Miguel A; Nelson, Tammie; Roitberg, Adrian E; Tretiak, Sergei; Fernandez-Alberti, Sebastian

    2014-11-13

    Using analytical excited-state gradients, vibrational normal modes have been calculated at the minimum of the electronic excited-state potential energy surfaces for a set of extended conjugated molecules with different coupling between them. Molecular model systems composed of units of polyphenylene ethynylene (PPE), polyphenylenevinylene (PPV), and naphthacene/pentacene (NP) have been considered. In all cases except the NP model, the influence of the nonadiabatic coupling on the excited-state equilibrium normal modes is revealed as a unique highest frequency adiabatic vibrational mode that overlaps with the coupling vector. This feature is removed by using a locally diabatic representation in which the effect of NA interaction is removed. Comparison of the original adiabatic modes with a set of vibrational modes computed in the locally diabatic representation demonstrates that the effect of nonadiabaticity is confined to only a few modes. This suggests that the nonadiabatic character of a molecular system may be detected spectroscopically by identifying these unique state-specific high frequency vibrational modes. PMID:24844735

  17. Controlling autoionization in strontium two-electron-excited states

    NASA Astrophysics Data System (ADS)

    Fields, Robert; Zhang, Xinyue; Dunning, F. Barry; Yoshida, Shuhei; Burgdörfer, Joachim

    2016-05-01

    One challenge in engineering long-lived two-electron-excited states, i.e., so-called planetary atoms, is autoionization. Autoionization, however, can be suppressed if the outermost electron is placed in a high- n, n ~ 300 - 600 , high- L state because such states have only a very small overlap with the inner electron, even when this is also excited to a state of relatively high n and hence of relatively long lifetime. Here the L-dependence of the autoionization rate for high- n strontium Rydberg atoms is examined during excitation of the core ion 5 s 2S1 / 2 - 5 p 2P3 / 2 transition. Measurements in which the angular momentum of the Rydberg electron is controlled using a pulsed electric field show that the autoionization rate decreases rapidly with increasing L and becomes very small for values larger than ~ 20 . The data are analyzed with the aid of calculations undertaken using complex scaling. Research supported by the NSF and Robert A. Welch Foundation.

  18. Excited states in the heavy nuclide {sup 254}No

    SciTech Connect

    Kankaanpaeae, H.; Leino, M.; Cocks, J. F. C.; Dorvaux, O.; Helariutta, K.; Jones, P.; Julin, R.; Juutinen, S.; Kettunen, H.; Kuusiniemi, P.; Muikku, M.; Nieminen, P.; Rahkila, P.; Savelius, A.; Trzaska, W. H.; Herzberg, R.-D.; Chewter, A. J.; Butler, P. A.; Greenlees, P. T.; Jones, G. D.

    1999-11-16

    In-beam {gamma}-ray spectroscopy of the excited states in the heavy nuclide {sup 254}No have been studied in the reaction {sup 208}Pb({sup 48}Ca,2n){sup 254}No. The techniques of recoil-gating and recoil-decay-tagging were needed due to the dominant fission background. Prompt {gamma}-rays were detected with a Ge detector array, consisting of four clover detectors in close geometry, and a gas-filled recoil separator (RITU) was used for detecting recoils and their {alpha}-decays. The observed six {gamma}-rays were associated with E2-transitions in the ground state rotational band of {sup 254}No. The value {beta}{sub 2}=0.27{+-}0.03 was extracted for the quadrupole deformation from the extrapolated 2{sup +} excitation energy.

  19. Photoionization of potassium atoms from the ground and excited states

    SciTech Connect

    Zatsarinny, O.; Tayal, S. S.

    2010-04-15

    The Dirac-based B-spline R-matrix method is used to investigate the photoionization of atomic potassium from the 4s ground and 4p, 5s-7s, 3d-5d excited states. The effect of the core polarization by the outer electron is included through the polarized pseudostates. Besides the dipole core polarization, we also found a noticeable influence of the quadrupole core polarization. We obtained excellent agreement with experiment for cross sections of the 4s photoionization, including accurate description of the near-threshold Cooper-Seaton minimum. We also obtained close agreement with experiment for the 4p photoionization, but there are unexpectedly large discrepancies with available experimental data for photoionization of the 5d and 7s excited states.

  20. Tunable rubidium excited state Voigt atomic optical filter.

    PubMed

    Yin, Longfei; Luo, Bin; Xiong, Junyu; Guo, Hong

    2016-03-21

    A tunable rubidium excited state Voigt atomic optical filter working at optical communication wavelength (1.5 μm) is realized. The filter achieves a peak transmittance of 57.6% with a double-peak structure, in which each one has a bandwidth of 600 MHz. Benefiting from the Voigt type structure, the magnetic field of the filter can be tuned from 0 to 1600 gauss, and a peak transmittance tunability of 1.6 GHz can thus be realized. Different from the excited state Faraday type filter, the pump efficiency in the Voigt filter is affected a lot by the pump polarization. Measured absorption results of the pump laser and transmittances of the signal laser both prove that the vertical linear polarization pumping is the most efficient in the Voigt filter. PMID:27136803

  1. Excited states in large molecular systems through polarizable embedding.

    PubMed

    List, Nanna Holmgaard; Olsen, Jógvan Magnus Haugaard; Kongsted, Jacob

    2016-07-27

    In this perspective, we provide an overview of recent work within the polarizable embedding scheme to describe properties of molecules in realistic environments of increasing complexity. After an outline of the theoretical basis for the polarizable embedding model, we discuss the importance of using an accurate embedding potential, and how this may be used to significantly reduce the size of the part of the system treated using quantum mechanics without compromising the accuracy of the final results. Furthermore, we discuss the calculation of local electronic excited states based on response theory. We finally discuss aspects related to two recent extensions of the model (i) effective external field and (ii) polarizable density embedding emphasizing their importance for efficient yet accurate description of excited-state properties in complex environments. PMID:27416749

  2. Compilation of giant electric dipole resonances built on excited states

    SciTech Connect

    Schiller, A. . E-mail: schiller@nscl.msu.edu; Thoennessen, M.

    2007-07-15

    Giant Electric Dipole Resonance (GDR) parameters for {gamma} decay to excited states with finite spin and temperature are compiled. Over 100 original works have been reviewed and from some 70 of them, about 350 sets of hot GDR parameters for different isotopes, excitation energies, and spin regions have been extracted. All parameter sets have been brought onto a common footing by calculating the equivalent Lorentzian parameters. The current compilation is complementary to an earlier compilation by Samuel S. Dietrich and Barry L. Berman (At. Data Nucl. Data Tables 38 (1988) 199-338) on ground-state photo-neutron and photo-absorption cross sections and their Lorentzian parameters. A comparison of the two may help shed light on the evolution of GDR parameters with temperature and spin. The present compilation is current as of July 2006.

  3. Physical Properties, Exciton Analysis, and Visualization of Core-Excited States: An Intermediate State Representation Approach.

    PubMed

    Wenzel, Jan; Dreuw, Andreas

    2016-03-01

    The theoretical simulation of X-ray absorption spectra is in general a challenging task. However, for small and medium-sized organic molecules, the algebraic diagrammatic construction scheme (ADC) for the polarization operator in combination with the core-valence separation approximation (CVS) has proven to yield core-excitation energies and transition moments with almost quantitative accuracy allowing for reliable construction of X-ray absorption spectra. Still, to understand core-excitation processes in detail, it is not sufficient to only compute energies, but also properties like static dipole moments and state densities are important as they provide deeper insight into the nature of core-excited states. Here, we present for the first time an implementation of the intermediate state representation (ISR) approach in combination with the CVS approximation (CVS-ISR), which gives, in combination with the CVS-ADC method, direct access to core-excited state properties. The performance of the CVS-ADC/CVS-ISR approach is demonstrated by means of small- and medium-sized organic molecules. Besides the calculation of core-excited state dipole moments, advanced analyses of core-excited state densities are performed using descriptors like exciton sizes and distances. Plotting electron and hole densities helps to determine the character of the state, and in particular, the investigation of detachment/attachment densities provides information about orbital relaxation effects that are crucial for understanding core excitations.

  4. Temperature dependence of the excited state absorption of alexandrite

    SciTech Connect

    Shand, M.L.; Jenssen, H.P.

    1983-03-01

    The temperature dependence from 28 to 290/sup 0/C of the excited-state absorption cross section sigma /SUB 2a/ (E) in the gain wavelength region of alexandrite has been determined from the temperature dependence of the single pass gain (SPG) and of the fluorescence. sigma /SUB 2a/ (E) and the emission cross section increase with temperature at approximately the same rate.

  5. Connection between decoherence and excited state quantum phase transitions

    SciTech Connect

    Perez-Fernandez, P.; Arias, J. M.; Relano, A.; Dukelsky, J.; Garcia-Ramos, J. E.

    2010-04-26

    In this work we explore the relationship between an excited state quantum phase transition (ESQPT) and the phenomenon of quantum decoherence. For this purpose, we study how the decoherence is affected by the presence of a continuous ESQPT in the environment. This one is modeled as a two level boson system described by a Lipkin Hamiltonian. We will show that the decoherence of the system is maximal when the environment undergoes a continuous ESQPT.

  6. Minimal-excitation states for electron quantum optics using levitons.

    PubMed

    Dubois, J; Jullien, T; Portier, F; Roche, P; Cavanna, A; Jin, Y; Wegscheider, W; Roulleau, P; Glattli, D C

    2013-10-31

    The on-demand generation of pure quantum excitations is important for the operation of quantum systems, but it is particularly difficult for a system of fermions. This is because any perturbation affects all states below the Fermi energy, resulting in a complex superposition of particle and hole excitations. However, it was predicted nearly 20 years ago that a Lorentzian time-dependent potential with quantized flux generates a minimal excitation with only one particle and no hole. Here we report that such quasiparticles (hereafter termed levitons) can be generated on demand in a conductor by applying voltage pulses to a contact. Partitioning the excitations with an electronic beam splitter generates a current noise that we use to measure their number. Minimal-excitation states are observed for Lorentzian pulses, whereas for other pulse shapes there are significant contributions from holes. Further identification of levitons is provided in the energy domain with shot-noise spectroscopy, and in the time domain with electronic Hong-Ou-Mandel noise correlations. The latter, obtained by colliding synchronized levitons on a beam splitter, exemplifies the potential use of levitons for quantum information: using linear electron quantum optics in ballistic conductors, it is possible to imagine flying-qubit operation in which the Fermi statistics are exploited to entangle synchronized electrons emitted by distinct sources. Compared with electron sources based on quantum dots, the generation of levitons does not require delicate nanolithography, considerably simplifying the circuitry for scalability. Levitons are not limited to carrying a single charge, and so in a broader context n-particle levitons could find application in the study of full electron counting statistics. But they can also carry a fraction of charge if they are implemented in Luttinger liquids or in fractional quantum Hall edge channels; this allows the study of Abelian and non-Abelian quasiparticles in the

  7. Minimal-excitation states for electron quantum optics using levitons

    NASA Astrophysics Data System (ADS)

    Dubois, J.; Jullien, T.; Portier, F.; Roche, P.; Cavanna, A.; Jin, Y.; Wegscheider, W.; Roulleau, P.; Glattli, D. C.

    2013-10-01

    The on-demand generation of pure quantum excitations is important for the operation of quantum systems, but it is particularly difficult for a system of fermions. This is because any perturbation affects all states below the Fermi energy, resulting in a complex superposition of particle and hole excitations. However, it was predicted nearly 20 years ago that a Lorentzian time-dependent potential with quantized flux generates a minimal excitation with only one particle and no hole. Here we report that such quasiparticles (hereafter termed levitons) can be generated on demand in a conductor by applying voltage pulses to a contact. Partitioning the excitations with an electronic beam splitter generates a current noise that we use to measure their number. Minimal-excitation states are observed for Lorentzian pulses, whereas for other pulse shapes there are significant contributions from holes. Further identification of levitons is provided in the energy domain with shot-noise spectroscopy, and in the time domain with electronic Hong-Ou-Mandel noise correlations. The latter, obtained by colliding synchronized levitons on a beam splitter, exemplifies the potential use of levitons for quantum information: using linear electron quantum optics in ballistic conductors, it is possible to imagine flying-qubit operation in which the Fermi statistics are exploited to entangle synchronized electrons emitted by distinct sources. Compared with electron sources based on quantum dots, the generation of levitons does not require delicate nanolithography, considerably simplifying the circuitry for scalability. Levitons are not limited to carrying a single charge, and so in a broader context n-particle levitons could find application in the study of full electron counting statistics. But they can also carry a fraction of charge if they are implemented in Luttinger liquids or in fractional quantum Hall edge channels; this allows the study of Abelian and non-Abelian quasiparticles in the

  8. Ultrafast internal conversion in ethylene. I. The excited state lifetime

    NASA Astrophysics Data System (ADS)

    Tao, H.; Allison, T. K.; Wright, T. W.; Stooke, A. M.; Khurmi, C.; van Tilborg, J.; Liu, Y.; Falcone, R. W.; Belkacem, A.; Martinez, T. J.

    2011-06-01

    Using a combined theoretical and experimental approach, we investigate the non-adiabatic dynamics of the prototypical ethylene (C2H4) molecule upon π → π* excitation. In this first part of a two part series, we focus on the lifetime of the excited electronic state. The femtosecond time-resolved photoelectron spectrum (TRPES) of ethylene is simulated based on our recent molecular dynamics simulation using the ab initio multiple spawning method with multi-state second order perturbation theory [H. Tao, B. G. Levine, and T. J. Martinez, J. Phys. Chem. A 113, 13656 (2009)], 10.1021/jp9063565. We find excellent agreement between the TRPES calculation and the photoion signal observed in a pump-probe experiment using femtosecond vacuum ultraviolet (hν = 7.7 eV) pulses for both pump and probe. These results explain the apparent discrepancy over the excited state lifetime between theory and experiment that has existed for ten years, with experiments [e.g., P. Farmanara, V. Stert, and W. Radloff, Chem. Phys. Lett. 288, 518 (1998), 10.1016/S0009-2614(98)00312-1 and K. Kosma, S. A. Trushin, W. Fuss, and W. E. Schmid, J. Phys. Chem. A 112, 7514 (2008)], 10.1021/jp803548c reporting much shorter lifetimes than predicted by theory. Investigation of the TRPES indicates that the fast decay of the photoion yield originates from both energetic and electronic factors, with the energetic factor playing a larger role in shaping the signal.

  9. Note: Excited State Studies of Ozone using State-Specific Multireference Coupled Cluster Methods

    SciTech Connect

    Bhaskaran-Nair, Kiran; Kowalski, Karol

    2012-12-07

    Vertical excitation energies obtained with state-specific multi-reference coupled cluster (MRCC) methods are reported for the ozone molecule. Using state-specific MRCC non-iterative methods with singles, doubles, and non-iterative triples (MRCCSD(T)) we obtain 4.40 eV for the challenging doubly excited 21A1 state when using a reliable model space. This estimate is in good agreement with experiment (4.5 eV). We also compare our MRCC results with the excitation energies obtained with high-order equation-of-motion coupled cluster methods

  10. Excited State Dynamics of Protonated Phenylalanine and Tyrosine: Photo-Induced Reactions Following Electronic Excitation.

    PubMed

    Féraud, Géraldine; Broquier, Michel; Dedonder, Claude; Jouvet, Christophe; Grégoire, Gilles; Soorkia, Satchin

    2015-06-11

    The electronic spectroscopy and the electronic excited state properties of cold protonated phenylalanine and protonated tyrosine have been revisited on a large spectral domain and interpreted by comparison with ab initio calculations. The protonated species are stored in a cryogenically cooled Paul trap, maintained at ∼10 K, and the parent and all the photofragment ions are mass-analyzed in a time-of-flight mass spectrometer, which allows detecting the ionic species with an improved mass resolution compared to what is routinely achieved with a quadrupole mass spectrometer. These new results emphasize the competition around the band origin between two proton transfer reactions from the ammonium group toward either the aromatic chromophore or the carboxylic acid group. These reactions are initiated by the coupling of the locally excited ππ* state with higher charge transfer states, the positions and coupling of which depend on the conformation of the protonated molecules. Each of these reaction processes gives rise to specific fragmentation channels that supports the conformer selectivity observed in the photofragmentation spectra of protonated tyrosine and phenylalanine.

  11. Delayed fluorescence during the deactivation of highly excited triplet states

    SciTech Connect

    Skvortsov, V.I.; Alfimov, M.V.

    1987-06-01

    It has been suggested that the T state may be not only an electron donor but an acceptor, i.e., it may give a charge transfer state in a photoreduction reaction: A(T) + M ..-->.. /sup 3/(A/sup .-/M/sup +./). In this connection, it may be assumed that the quenching may also be connected with the nonradiative deactivation of excitation energy in charge transfer states (A/sup .-/M/sup +./). Aromatic molecules are characterized by an extremely low quantum yield for intramolecular intersystem crossing. However, in charge-transfer states the efficiency of intersystem crossing may be enhanced. The authors have investigated the laws governing DF in conditions where the deactivation of T states occurs. The systems studied were frozen (77 K) solutions of the aromatic additives naphthalene, diphenyl, and chrysene in toluene, MCH, and ethanol.

  12. An incompressible state of a photo-excited electron gas

    PubMed Central

    Chepelianskii, Alexei D.; Watanabe, Masamitsu; Nasyedkin, Kostyantyn; Kono, Kimitoshi; Konstantinov, Denis

    2015-01-01

    Two-dimensional electrons in a magnetic field can form new states of matter characterized by topological properties and strong electronic correlations as displayed in the integer and fractional quantum Hall states. In these states, the electron liquid displays several spectacular characteristics, which manifest themselves in transport experiments with the quantization of the Hall resistance and a vanishing longitudinal conductivity or in thermodynamic equilibrium when the electron fluid becomes incompressible. Several experiments have reported that dissipationless transport can be achieved even at weak, non-quantizing magnetic fields when the electrons absorb photons at specific energies related to their cyclotron frequency. Here we perform compressibility measurements on electrons on liquid helium demonstrating the formation of an incompressible electronic state under these resonant excitation conditions. This new state provides a striking example of irradiation-induced self-organization in a quantum system. PMID:26007282

  13. Excited states of the helium-antihydrogen system.

    PubMed

    Sharipov, Vasily; Labzowsky, Leonti N; Plunien, Günter

    2007-03-01

    Potential energy curves for excited leptonic states of the helium-antihydrogen system are calculated within the Ritz variational approach. An explicitly correlated ansatz for the leptonic wave function is employed describing accurately the motion of the leptons (two electrons and positron) in the field of the helium nucleus and of the antiproton with an arbitrary orbital angular momentum projection Lambda onto the internuclear axis. Results for Lambda=0, 1, and 30 are presented. For quasibound states with large values of Lambda and rotational quantum numbers J>Lambda no annihilation and rearrangement decay channels occur; i.e., they are metastable.

  14. Modular Hamiltonian for Excited States in Conformal Field Theory

    NASA Astrophysics Data System (ADS)

    Lashkari, Nima

    2016-07-01

    We present a novel replica trick that computes the relative entropy of two arbitrary states in conformal field theory. Our replica trick is based on the analytic continuation of partition functions that break the Zn replica symmetry. It provides a method for computing arbitrary matrix elements of the modular Hamiltonian corresponding to excited states in terms of correlation functions. We show that the quantum Fisher information in vacuum can be expressed in terms of two-point functions on the replica geometry. We perform sample calculations in two-dimensional conformal field theories.

  15. Modular Hamiltonian for Excited States in Conformal Field Theory.

    PubMed

    Lashkari, Nima

    2016-07-22

    We present a novel replica trick that computes the relative entropy of two arbitrary states in conformal field theory. Our replica trick is based on the analytic continuation of partition functions that break the Z_{n} replica symmetry. It provides a method for computing arbitrary matrix elements of the modular Hamiltonian corresponding to excited states in terms of correlation functions. We show that the quantum Fisher information in vacuum can be expressed in terms of two-point functions on the replica geometry. We perform sample calculations in two-dimensional conformal field theories. PMID:27494465

  16. Leptonic partial widths of the excited {psi} states

    SciTech Connect

    Mo, X. H.; Yuan, C. Z.; Wang, P.

    2010-10-01

    The resonance parameters of the excited {psi}-family resonances, namely, the {psi}(4040), {psi}(4160), and {psi}(4415), were determined by fitting the R values measured by experiments. It is found that the previously reported leptonic partial widths of these states were merely one possible solution among a four-fold ambiguity. By fitting the most precise experimental data on the R values measured by the BES collaboration, this work presents all four sets of solutions. These results may affect the interpretation of the charmonium and charmonium-like states above 4 GeV/c{sup 2}.

  17. Modular Hamiltonian for Excited States in Conformal Field Theory.

    PubMed

    Lashkari, Nima

    2016-07-22

    We present a novel replica trick that computes the relative entropy of two arbitrary states in conformal field theory. Our replica trick is based on the analytic continuation of partition functions that break the Z_{n} replica symmetry. It provides a method for computing arbitrary matrix elements of the modular Hamiltonian corresponding to excited states in terms of correlation functions. We show that the quantum Fisher information in vacuum can be expressed in terms of two-point functions on the replica geometry. We perform sample calculations in two-dimensional conformal field theories.

  18. The safe removal of frozen air from the annulus of an LH2 storage tank

    NASA Astrophysics Data System (ADS)

    Krenn, A.; Starr, S.; Youngquist, R.; Nurge, M.; Sass, J.; Fesmire, J.; Cariker, C.; Bhattacharya, A.

    2015-12-01

    Large Liquid Hydrogen (LH2) storage tanks are vital infrastructure for NASA. Eventually, air may leak into the evacuated and perlite filled annular region of these tanks. Although the vacuum level is monitored in this region, the extremely cold temperature causes all but the helium and neon constituents of air to freeze. A small, often unnoticeable pressure rise is the result. As the leak persists, the quantity of frozen air increases, as does the thermal conductivity of the insulation system. Consequently, a notable increase in commodity boil-off is often the first indicator of an air leak. Severe damage can result from normal draining of the tank. The warming air will sublimate which will cause a pressure rise in the annulus. When the pressure increases above the triple point, the frozen air will begin to melt and migrate downward. Collection of liquid air on the carbon steel outer shell may chill it below its ductility range, resulting in fracture. In order to avoid a structural failure, as described above, a method for the safe removal of frozen air is needed. A thermal model of the storage tank has been created using SINDA/FLUINT modelling software. Experimental work is progressing in an attempt to characterize the thermal conductivity of a perlite/frozen nitrogen mixture. A statistical mechanics model is being developed in parallel for comparison to experimental work. The thermal model will be updated using the experimental/statistical mechanical data, and used to simulate potential removal scenarios. This paper will address methodologies and analysis techniques for evaluation of two proposed air removal methods.

  19. Northrop Grumman TR202 LOX/LH2 Deep Throttling Engine Technology Project Status

    NASA Technical Reports Server (NTRS)

    Gromski, Jason; Majamaki, Annik; Chianese, Silvio; Weinstock, Vladimir; Kim, Tony S.

    2010-01-01

    NASA's Propulsion and Cryogenic Advanced Development (PCAD) project is currently developing enabling propulsion technologies in support of future lander missions. To meet lander requirements, several technical challenges need to be overcome, one of which is the ability for the descent engine(s) to operate over a deep throttle range with cryogenic propellants. To address this need, PCAD has enlisted Northrop Grumman Aerospace Systems (NGAS) in a technology development effort associated with the TR202 engine. The TR202 is a LOX/LH2 expander cycle engine driven by independent turbopump assemblies and featuring a variable area pintle injector similar to the injector used on the TR200 Apollo Lunar Module Descent Engine (LMDE). Since the Apollo missions, NGAS has continued to mature deep throttling pintle injector technology. The TR202 program has completed two series of pintle injector testing. The first series of testing used ablative thrust chambers and demonstrated igniter operation as well as stable performance at discrete points throughout the designed 10:1 throttle range. The second series was conducted with calorimeter chambers and demonstrated injector performance at discrete points throughout the throttle range as well as chamber heat flow adequate to power an expander cycle design across the throttle range. This paper provides an overview of the TR202 program, describing the different phases and key milestones. It describes how test data was correlated to the engine conceptual design. The test data obtained has created a valuable database for deep throttling cryogenic pintle technology, a technology that is readily scalable in thrust level.

  20. The Safe Removal of Frozen Air from the Annulus of an LH2 Storage Tank

    NASA Technical Reports Server (NTRS)

    Krenn, A.; Starr, S.; Youngquist, R.; Nurge, M.; Sass, J.; Fesmire, J.; Cariker, C.; Bhattacharya, A.

    2015-01-01

    Large Liquid Hydrogen (LH2) storage tanks are vital infrastructure for NASA. Eventually, air may leak into the evacuated and perlite filled annular region of these tanks. Although the vacuum level is monitored in this region, the extremely cold temperature causes all but the helium and neon constituents of air to freeze. A small, often unnoticeable pressure rise is the result. As the leak persists, the quantity of frozen air increases, as does the thermal conductivity of the insulation system. Consequently, a notable increase in commodity boil-off is often the first indicator of an air leak. Severe damage can result from normal draining of the tank. The warming air will sublimate which will cause a pressure rise in the annulus. When the pressure increases above the triple point, the frozen air will begin to melt and migrate downward. Collection of liquid air on the carbon steel outer shell may chill it below its ductility range, resulting in fracture. In order to avoid a structural failure, as described above, a method for the safe removal of frozen air is needed. A thermal model of the storage tank has been created using SINDA/FLUINT modeling software. Experimental work is progressing in an attempt to characterize the thermal conductivity of a perlite/frozen nitrogen mixture. A statistical mechanics model is being developed in parallel for comparison to experimental work. The thermal model will be updated using the experimental/statistical mechanical data, and used to simulate potential removal scenarios. This paper will address methodologies and analysis techniques for evaluation of two proposed air removal methods.

  1. Operational Issues in the Development of a Cost-Effective Reusable LOX/LH2 Engine

    NASA Technical Reports Server (NTRS)

    Ballard, Richard O.

    2003-01-01

    The NASA Space Launch Initiative (SLI) was initiated in early 2001 to conduct technology development and to reduce the business and technical risk associated with developing the next-generation reusable launch system. In the field of main propulsion, two LOXLH2 rocket engine systems, the Pratt & Whitney / Aerojet Joint Venture (JV) COBRA and the Rocketdyne RS-83, were funded to develop a safe, economical, and reusable propulsion system. Given that a large-thrust reusable rocket engine program had not been started in the U.S. since 1971, with the Space Shuttle Main Engine (SSME), this provided an opportunity to build on the experience developed on the SSME system, while exploiting advances in technology that had occurred in the intervening 30 years. One facet of engine development that was identified as being especially vital in order to produce an optimal system was in the areas of operability and maintainability. In order to achieve the high levels of performance required by the Space Shuttle, the SSME system is highly complex with very tight tolerances and detailed requirements. Over the lifetime of the SSME program, the engine has required a high level of manpower to support the performance of inspections, maintenance (scheduled and unscheduled) and operations (prelaunch and post-flight). As a consequence, the labor- intensive needs of the SSME provide a significant impact to the overall cost efficiency of the Space Transportation System (STS). One of the strategic goals of the SLI is to reduce cost by requiring the engine(s) to be easier (Le. less expensive) to operate and maintain. The most effective means of accomplishing this goal is to infuse the operability and maintainability features into the engine design from the start. This paper discusses some of the operational issues relevant to a reusable LOx/LH2 main engine, and the means by which their impact is mitigated in the design phase.

  2. Observation of the highly excited states of Lanthanum

    SciTech Connect

    Xue, P.; Xu, X. Y.; Huang, W.; Xu, C. B.; Zhao, R. C.; Xie, X. P.

    1997-01-15

    The highly excited states of Lanthanum are studied by means of laser resonance ionization time-of-flight spectrometer. Based on the two-step laser resonance excitation with intermediate state 5d{sup 2}({sup 3}F)6p {sup 2}D{sub 5/2}{sup 0}, three new Rydberg state (RS) series (5d{sup 2}(a{sup 3}F{sub 2})ns, 5d{sup 2}(a{sup 3}F{sub 3})nd and 5d{sup 2}(a{sup 1}D{sub 2})ns) and a number of autoionizing states (AIS) are obtained. Theoretical calculation leads the quantum defects of ns and nd series to the value {delta}s=4.35 and {delta}{sub d}=2.80 respectively, which are very close to the experimental results. The Rydberg state series 5d{sup 2}(a{sup 3}F{sub 2})ns gives the first ionization limit to be 44979.8{+-}0.3 cm{sup -1}, which is an order more accurate than ever.

  3. Observation of interference effects via four-photon excitation of highly excited Rydberg states in thermal cesium vapor

    NASA Astrophysics Data System (ADS)

    Kondo, Jorge M.; Šibalić, Nikola; Guttridge, Alexander; Wade, Christopher G.; De Melo, Natalia R.; Adams, Charles S.; Weatherill, Kevin J.

    2015-12-01

    We report on the observation of electromagnetically induced transparency (EIT) and absorption (EIA) of highly excited Rydberg states in thermal Cs vapor using a four-step excitation scheme. The advantage of this four-step scheme is that the final transition to the Rydberg state has a large dipole moment and one can achieve similar Rabi frequencies to two- or three-step excitation schemes using two orders of magnitude less laser power. This scheme enables new applications such as dephasing free Rydberg excitation. The observed lineshapes are in good agreement with simulations based on multilevel optical Bloch equations.

  4. Excited states in 146Sm and 147Sm

    NASA Astrophysics Data System (ADS)

    Kownacki, J.; Sujkowski, Z.; Hammarén, E.; Liukkonen, E.; Piiparinen, M.; Lindblad, Th.; Ryde, H.; Paar, V.

    1980-03-01

    The 144, 146Nd(α, χn) and 146,148Nd( 3He, χn) reactions with Eα = 20-43 MeV and E3He , = 19-27 MeV are used to investigate excited states in the isotopes 146Sm and 147Sm. The experiments involve measurements of singles γ-ray spectra and conversion electron spectra, γ-ray angular distributions and three-parameter ( Eγ- Eγ-time) coincidences. From these experiments information is obtained for states with spin up to I = 13 +and I = {27}/{2}-, respectively. These states are interpreted within the framework of the cluster-vibration model (CVM) as well as the shell model. In the latter approach, the energies of several well established states, in both isotopes, are calculated using empirical singleparticle energies, empirical two-particle interaction matrix elements and angular momentum algebra. The average deviation between the calculated and the experimental energies is less than 100 keV. The CVM calculations involve the coupling of a three-particle neutron cluster to the quadrupole vibration of the core. For 147Sm, these calculations reproduce the observed sequence of states based on the I π = {7}/{2}- ground state, as well as the sequence of states based on the I π = {13}/{2}+ excited state. The CVM calculations also reproduce the ground band in 146Sm, while for the negative parity states based on the cluster (f {7}/{2}i {13}/{2}) 3 --10 - an additional shift in energy is expected due to the mixing with octupole phonons.

  5. Excited-State Properties of Molecular Solids from First Principles.

    PubMed

    Kronik, Leeor; Neaton, Jeffrey B

    2016-05-27

    Molecular solids have attracted attention recently in the context of organic (opto)electronics. These materials exhibit unique charge carrier generation and transport phenomena that are distinct from those of conventional semiconductors. Understanding these phenomena is fundamental to optoelectronics and requires a detailed description of the excited-state properties of molecular solids. Recent advances in many-body perturbation theory (MBPT) and density functional theory (DFT) have made such description possible and have revealed many surprising electronic and optical properties of molecular crystals. Here, we review this progress. We summarize the salient aspects of MBPT and DFT as well as various properties that can be described by these methods. These properties include the fundamental gap and its renormalization, hybridization and band dispersion, singlet and triplet excitations, optical spectra, and excitonic properties. For each, we present concrete examples, a comparison to experiments, and a critical discussion.

  6. Excited-State Properties of Molecular Solids from First Principles.

    PubMed

    Kronik, Leeor; Neaton, Jeffrey B

    2016-05-27

    Molecular solids have attracted attention recently in the context of organic (opto)electronics. These materials exhibit unique charge carrier generation and transport phenomena that are distinct from those of conventional semiconductors. Understanding these phenomena is fundamental to optoelectronics and requires a detailed description of the excited-state properties of molecular solids. Recent advances in many-body perturbation theory (MBPT) and density functional theory (DFT) have made such description possible and have revealed many surprising electronic and optical properties of molecular crystals. Here, we review this progress. We summarize the salient aspects of MBPT and DFT as well as various properties that can be described by these methods. These properties include the fundamental gap and its renormalization, hybridization and band dispersion, singlet and triplet excitations, optical spectra, and excitonic properties. For each, we present concrete examples, a comparison to experiments, and a critical discussion. PMID:27090844

  7. Excited-State Properties of Molecular Solids from First Principles

    NASA Astrophysics Data System (ADS)

    Kronik, Leeor; Neaton, Jeffrey B.

    2016-05-01

    Molecular solids have attracted attention recently in the context of organic (opto)electronics. These materials exhibit unique charge carrier generation and transport phenomena that are distinct from those of conventional semiconductors. Understanding these phenomena is fundamental to optoelectronics and requires a detailed description of the excited-state properties of molecular solids. Recent advances in many-body perturbation theory (MBPT) and density functional theory (DFT) have made such description possible and have revealed many surprising electronic and optical properties of molecular crystals. Here, we review this progress. We summarize the salient aspects of MBPT and DFT as well as various properties that can be described by these methods. These properties include the fundamental gap and its renormalization, hybridization and band dispersion, singlet and triplet excitations, optical spectra, and excitonic properties. For each, we present concrete examples, a comparison to experiments, and a critical discussion.

  8. Enhanced non-Gaussianity from excited initial states

    SciTech Connect

    Holman, R; Tolley, Andrew J E-mail: atolley@perimeterinstitute.ca

    2008-05-15

    We use the techniques of effective field theory in an expanding universe to examine the effect of choosing an excited inflationary initial state built over the Bunch-Davies state on the CMB bi-spectrum. We find that, even for Hadamard states, there are unexpected enhancements in the bi-spectrum for certain configurations in momentum space due to interactions of modes in the early stages of inflation. These enhancements can be parametrically larger than the standard ones and are potentially observable in future data. These initial state effects have a characteristic signature in l-space which distinguishes them from the usual contributions, with the enhancement being most pronounced for configurations corresponding to flattened triangles for which two momenta are collinear.

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

    SciTech Connect

    Alagia, M.; Coreno, M.; Farrokhpour, H.; Omidyan, R.; Tabrizchi, M.; Franceschi, P.; Mihelic, A.; Zitnik, M.; Moise, A.; Prince, K. C.; Richter, R.; Soederstroem, J.; Stranges, S.

    2009-04-17

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

  10. Radiative lifetimes of the bound excited states of Pt-

    NASA Astrophysics Data System (ADS)

    Chartkunchand, K. C.; Kamińska, M.; Anderson, E. K.; Kristiansson, M. K.; Eklund, G.; Hole, O. M.; Nascimento, R. F.; Blom, M.; Björkhage, M.; Källberg, A.; Löfgren, P.; Reinhed, P.; Rosén, S.; Simonsson, A.; Thomas, R. D.; Mannervik, S.; Davis, V. T.; Neill, P. A.; Thompson, J. S.; Hanstorp, D.; Zettergren, H.; Cederquist, H.; Schmidt, H. T.

    2016-09-01

    The intrinsic radiative lifetimes of the 5 d106 s1/2 2S and 5 d96 s2 3/2 2D bound excited states in the platinum anion Pt-have been studied at cryogenic temperatures at the Double ElectroStatic Ion Ring Experiment (DESIREE) facility at Stockholm University. The intrinsic lifetime of the higher-lying 5 d106 s 1/2 2S state was measured to be 2.54 ±0.10 s , while only a lifetime in the range of 50-200 ms could be estimated for the 5 d96 s2 3/2 2D fine-structure level. The storage lifetime of the Pt- ion beam was measured to be a little over 15 min at a ring temperature of 13 K . The present study reports the lifetime of an atomic negative ion in an excited bound state with an electron configuration different from that of the ground state.

  11. Radiative lifetimes of the bound excited states of Pt-

    NASA Astrophysics Data System (ADS)

    Chartkunchand, K. C.; Kamińska, M.; Anderson, E. K.; Kristiansson, M. K.; Eklund, G.; Hole, O. M.; Nascimento, R. F.; Blom, M.; Björkhage, M.; Källberg, A.; Löfgren, P.; Reinhed, P.; Rosén, S.; Simonsson, A.; Thomas, R. D.; Mannervik, S.; Davis, V. T.; Neill, P. A.; Thompson, J. S.; Hanstorp, D.; Zettergren, H.; Cederquist, H.; Schmidt, H. T.

    2016-09-01

    The intrinsic radiative lifetimes of the 5 d106 s 1/2 2S and 5 d96 s2 3/2 2D bound excited states in the platinum anion Pt-have been studied at cryogenic temperatures at the Double ElectroStatic Ion Ring Experiment (DESIREE) facility at Stockholm University. The intrinsic lifetime of the higher-lying 5 d106 s 1/2 2S state was measured to be 2.54 ±0.10 s , while only a lifetime in the range of 50-200 ms could be estimated for the 5 d96 s2 3/2 2D fine-structure level. The storage lifetime of the Pt- ion beam was measured to be a little over 15 min at a ring temperature of 13 K . The present study reports the lifetime of an atomic negative ion in an excited bound state with an electron configuration different from that of the ground state.

  12. Self-scattering for Dark Matter with an excited state

    SciTech Connect

    Schutz, Katelin; Slatyer, Tracy R. E-mail: tslatyer@mit.edu

    2015-01-01

    Self-interacting dark matter scenarios have recently attracted much attention, as a possible means to alleviate the tension between N-body simulations and observations of the dark matter distribution on galactic and sub-galactic scales. The presence of internal structure for the dark matter—for example, a nearly-degenerate state in the spectrum that could decay, or be collisionally excited or de-excited—has also been proposed as a possible means to address these discrepancies. Such internal structure can be a source of interesting signatures in direct and indirect dark matter searches, for example providing a novel explanation for the 3.5 keV line recently observed in galaxies and galaxy clusters. We analyze a simple model of dark matter self-scattering including a nearly-degenerate excited state, and develop an accurate analytic approximation for the elastic and inelastic s-wave cross sections, which is valid outside the perturbative regime provided the particle velocity is sufficiently low (this condition is also required for the s-wave to dominate over higher partial waves). We anticipate our results will be useful in incorporating inelastic self-scattering into N-body simulations, in order to study the quantitative impact of nearly-degenerate states in the dark matter spectrum on galactic structure and dynamics, and in computing the indirect signatures of multi-state dark matter.

  13. Excited state dynamics and isomerization in ruthenium sulfoxide complexes.

    PubMed

    King, Albert W; Wang, Lei; Rack, Jeffrey J

    2015-04-21

    Molecular photochromic compounds are those that interconvert between two isomeric forms with light. The two isomeric forms display distinct electronic and molecular structures and must not be in equilibrium with one another. These light-activated molecular switch compounds have found wide application in areas of study ranging from chemical biology to materials science, where conversion from one isomeric form to another by light prompts a response in the environment (e.g., protein or polymeric material). Certain ruthenium and osmium polypyridine sulfoxide complexes are photochromic. The mode of action is a phototriggered isomerization of the sulfoxide from S- to O-bonded. The change in ligation drastically alters both the spectroscopic and electrochemical properties of the metal complex. Our laboratory has pioneered the preparation and study of these complexes. In particular, we have applied femtosecond pump-probe spectroscopy to reveal excited state details of the isomerization mechanism. The data from numerous complexes allowed us to predict that the isomerization was nonadiabatic in nature, defined as occurring from a S-bonded triplet excited state (primarily metal-to-ligand charge transfer in character) to an O-bonded singlet ground state potential energy surface. This prediction was corroborated by high-level density functional theory calculations. An intriguing aspect of this reactivity is the coupling of nuclear motion to the electronic wave function and how this coupling affects motions productive for isomerization. In an effort to learn more about this coupling, we designed a project to examine phototriggered isomerization in bis-sulfoxide complexes. The goal of these studies was to determine whether certain complexes could be designed in which a single photon excitation event would prompt two sulfoxide isomerizations. We employed chelating sulfoxides in this study and found that both the nature of the chelate ring and the R group on the sulfoxide affect

  14. Output power of a quantum dot laser: Effects of excited states

    SciTech Connect

    Wu, Yuchang; Jiang, Li Asryan, Levon V.

    2015-11-14

    A theory of operating characteristics of quantum dot (QD) lasers is discussed in the presence of excited states in QDs. We consider three possible situations for lasing: (i) ground-state lasing only; (ii) ground-state lasing at first and then the onset of also excited-state lasing with increasing injection current; (iii) excited-state lasing only. The following characteristics are studied: occupancies of the ground-state and excited-state in QDs, free carrier density in the optical confinement layer, threshold currents for ground- and excited-state lasing, densities of photons emitted via ground- and excited-state stimulated transitions, output power, internal and external differential quantum efficiencies. Under the conditions of ground-state lasing only, the output power saturates with injection current. Under the conditions of both ground- and excited-state lasing, the output power of ground-state lasing remains pinned above the excited-state lasing threshold while the power of excited-state lasing increases. There is a kink in the light-current curve at the excited-state lasing threshold. The case of excited-state lasing only is qualitatively similar to that for single-state QDs—the role of ground-state transitions is simply reduced to increasing the threshold current.

  15. Stepwise two-photon excited fluorescence from higher excited states of chlorophylls in photosynthetic antenna complexes.

    PubMed

    Leupold, Dieter; Teuchner, Klaus; Ehlert, Jürgen; Irrgang, Klaus-Dieter; Renger, Gernot; Lokstein, Heiko

    2006-09-01

    Stepwise two-photon excited fluorescence (TPEF) spectra of the photosynthetic antenna complexes PCP, CP47, CP29, and light-harvesting complex II (LHC II) were measured. TPEF emitted from higher excited states of chlorophyll (Chl) a and b was elicited via consecutive absorption of two photons in the Chl a/b Qy range induced by tunable 100-fs laser pulses. Global analyses of the TPEF line shapes with a model function for monomeric Chl a in a proteinaceous environment allow distinction between contributions from monomeric Chls a and b, strongly excitonically coupled Chls a, and Chl a/b heterodimers/-oligomers. The analyses indicate that the longest wavelength-absorbing Chl species in the Qy region of LHC II is a Chl a homodimer with additional contributions from adjacent Chl b. Likewise, in CP47 a spectral form at approximately 680 nm (that is, however, not the red-most species) is also due to strongly coupled Chls a. In contrast to LHC II, the red-most Chl subband of CP29 is due to a monomeric Chl a. The two Chls b in CP29 exhibit marked differences: a Chl b absorbing at approximately 650 nm is not excitonically coupled to other Chls. Based on this finding, the refractive index of its microenvironment can be determined to be 1.48. The second Chl b in CP29 (absorbing at approximately 640 nm) is strongly coupled to Chl a. Implications of the findings with respect to excitation energy transfer pathways and rates are discussed. Moreover, the results will be related to most recent structural analyses.

  16. Radiative Decays of Low-Lying Excited-State Hyperons

    SciTech Connect

    Simon Taylor

    2000-05-01

    The quark wave-functions of the lower-lying excited-state hyperons Lambda(1405), Sigma(1385), and Lambda(1520) are not well understood. For example, the Lambda(1405) may not be a regular three-quark state but a {bar K}N molecule. Several competing models have been proposed, but none have been convincingly eliminated. Measuring radiative decays provides a means of discriminating between the models. The radiative branching of ratios are predicted to be small ({approx}1%), but the radiative widths vary by factors of 2-10 from model to model. The existing experimental data is sparse and inconsistent; moreover, the radiative decay of the Sigma(1385) has never been observed before (except for one event). These lower-lying excited state hypersons were produced in a tagged photon-beam experiment in the CLAS detector at TJNAF in the reaction gamma p {yields} K{sup +} Y* for photon energies from threshold to 2.4 GeV. The radiative branching ration for the Sigma{sup 0}(1385) relative to the Sigma{sup 0}(1385) {yields} Lambda pi{sup 0} channel was measured to be 0.021 {+-} 0.008{sub -0.007}{sup +0.004}, corresponding to a partial width of 640 {+-} 270{sub -220}{sup +130} keV.

  17. Excited State Effects in Nucleon Matrix Element Calculations

    SciTech Connect

    Constantia Alexandrou, Martha Constantinou, Simon Dinter, Vincent Drach, Karl Jansen, Theodoros Leontiou, Dru B Renner

    2011-12-01

    We perform a high-statistics precision calculation of nucleon matrix elements using an open sink method allowing us to explore a wide range of sink-source time separations. In this way the influence of excited states of nucleon matrix elements can be studied. As particular examples we present results for the nucleon axial charge g{sub A} and for the first moment of the isovector unpolarized parton distribution x{sub u-d}. In addition, we report on preliminary results using the generalized eigenvalue method for nucleon matrix elements. All calculations are performed using N{sub f} = 2+1+1 maximally twisted mass Wilson fermions.

  18. Northrop Grumman TR202 LOX/LH2 Deep Throttling Engine Project Status

    NASA Technical Reports Server (NTRS)

    Gromski, J.; Majamaki, A. N.; Chianese, S. G.; Weinstock, V. D.; Kim, T.

    2010-01-01

    NASA's Propulsion and Cryogenic Advanced Development (PCAD) project is currently developing enabling propulsion technologies in support of the Exploration Initiative, with a particular focus on the needs of the Altair Project. To meet Altair requirements, several technical challenges need to be overcome, one of which is the ability for the lunar descent engine(s) to operate over a deep throttle range with cryogenic propellants. To address this need, PCAD has enlisted Northrop Grumman Aerospace Systems (NGAS) in a technology development effort associated with the TR202, a LOX/LH2 expander cycle engine driven by independent turbopump assemblies and featuring a variable area pintle injector similar to the injector used on the TR200 Apollo Lunar Module Descent Engine (LMDE). Since the Apollo missions, NGAS has continued to mature deep throttling pintle injector technology. The TR202 program has completed two phases of pintle injector testing. The first phase of testing used ablative thrust chambers and demonstrated igniter operation as well as stable performance at several power levels across the designed 10:1 throttle range. The second phase of testing was performed on a calorimeter chamber and demonstrated injector performance at various power levels (75%, 50%, 25%, 10%, and 7.5%) across the throttle range as well as chamber heat flux to show that the engine can close an expander cycle design across the throttle range. This paper provides an overview of the TR202 program. It describes the different phases of the program with the key milestones of each phase. It then shows when those milestones were met. Next, it describes how the test data was used to update the conceptual design and how the test data has created a database for deep throttling cryogenic pintle technology that is readily scaleable and can be used to again update the design once the Altair program's requirements are firm. The final section of the paper describes the path forward, which includes

  19. Excited-state relaxation in π-conjugated polymers

    NASA Astrophysics Data System (ADS)

    Frolov, S. V.; Bao, Z.; Wohlgenannt, M.; Vardeny, Z. V.

    2002-05-01

    We study ultrafast relaxation processes of odd- (Bu) and even-parity (Ag) exciton states in poly(p-phenylene vinylene) derivatives. The Bu states are studied using a regular two-beam pump-and-probe spectroscopy, which can monitor vibronic relaxation and exciton diffusion. In order to observe the Ag states, a three-beam femtosecond transient spectroscopy is developed, in which two different excitation pulses successively generate odd-parity (1Bu) excitons at 2.2 eV and then reexcite them to higher Ag states. We are able to distinguish two different classes of Ag states: one class (mAg) experiences ultrafast internal conversion back to the lowest singlet exciton, whereas the other class (kAg) in violation of the Vavilov-Kasha's rule undergoes a different relaxation pathway. The excitons subsequently dissociate into long-lived polaron pairs, which results in emission quenching with the action spectrum similar to that of the intrinsic photoconductivity. We conclude that the Ag states above 3.3 eV (kAg) are charge-transfer states, that mediate carrier photogeneration.

  20. Ground State and Excited State H-Atom Temperatures in a Microwave Plasma Diamond Deposition Reactor

    NASA Astrophysics Data System (ADS)

    Gicquel, A.; Chenevier, M.; Breton, Y.; Petiau, M.; Booth, J. P.; Hassouni, K.

    1996-09-01

    Ground electronic state and excited state H-atom temperatures are measured in a microwave plasma diamond deposition reactor as a function of a low percentage of methane introduced in the feed gas and the averaged input microwave power density. Ground state H-atom temperatures (T_H) and temperature of the H-atom in the n=3 excited state (T_{Hα}) are obtained from the measurements respectively of the excitation profile by Two-photon Allowed transition Laser Induced Fluorescence (TALIF) and the Hα line broadening by Optical Emission Spectroscopy (OES). They are compared to gas temperatures calculated with a 1D diffusive non equilibrium H{2} plasma flow model and to ground electronic state rotational temperatures of molecular hydrogen measured previously by Coherent Anti-Stokes Raman Spectroscopy.

  1. Calculating singlet excited states: Comparison with fast time-resolved infrared spectroscopy of coumarins

    NASA Astrophysics Data System (ADS)

    Hanson-Heine, Magnus W. D.; Wriglesworth, Alisdair; Uroos, Maliha; Calladine, James A.; Murphy, Thomas S.; Hamilton, Michelle; Clark, Ian P.; Towrie, Michael; Dowden, James; Besley, Nicholas A.; George, Michael W.

    2015-04-01

    In contrast to the ground state, the calculation of the infrared (IR) spectroscopy of molecular singlet excited states represents a substantial challenge. Here, we use the structural IR fingerprint of the singlet excited states of a range of coumarin dyes to assess the accuracy of density functional theory based methods for the calculation of excited state IR spectroscopy. It is shown that excited state Kohn-Sham density functional theory provides a high level of accuracy and represents an alternative approach to time-dependent density functional theory for simulating the IR spectroscopy of singlet excited states.

  2. Calculating singlet excited states: Comparison with fast time-resolved infrared spectroscopy of coumarins.

    PubMed

    Hanson-Heine, Magnus W D; Wriglesworth, Alisdair; Uroos, Maliha; Calladine, James A; Murphy, Thomas S; Hamilton, Michelle; Clark, Ian P; Towrie, Michael; Dowden, James; Besley, Nicholas A; George, Michael W

    2015-04-21

    In contrast to the ground state, the calculation of the infrared (IR) spectroscopy of molecular singlet excited states represents a substantial challenge. Here, we use the structural IR fingerprint of the singlet excited states of a range of coumarin dyes to assess the accuracy of density functional theory based methods for the calculation of excited state IR spectroscopy. It is shown that excited state Kohn-Sham density functional theory provides a high level of accuracy and represents an alternative approach to time-dependent density functional theory for simulating the IR spectroscopy of singlet excited states.

  3. Unbound Excited States in ^28Ne and ^25F

    NASA Astrophysics Data System (ADS)

    Smith, Jenna; Brown, B. Alex; Christian, Greg; Mosby, Shea; Novak, John F.; Quinn, Steven J.; Snyder, Jesse; Spyrou, Artemis; Strongman, Michael J.; Thoennessen, Michael; Baumann, Thomas; Kohley, Zachary; Finck, Joseph E.; Hoffman, Calem R.

    2012-10-01

    The neutron dripline has only been conclusively mapped out to Z=8. The unbound structure of isotopes with Z>8 has not been studied until recently, when multiple studies have focused on unbound states in neutron-rich fluorine isotopes. Unbound states in ^28Ne and ^25F were populated in the reaction of a 102 MeV/nucleon ^29Na beam on a beryllium target. This is the first such state in ^28Ne and the second such state in ^25F. The measured decay energy of 32(22) keV in the ^27Ne + n system corresponds to an unbound excited state in ^28Ne of 3.86(11) MeV. The decay energy of the ^24F + n system was measured as 300(170) keV, which places the second measured unbound state of ^25F at 4.66(17) MeV. Measured decay energy spectra and a discussion of results will be presented.

  4. Alpha decay widths of excited states of 16O

    NASA Astrophysics Data System (ADS)

    Haigh, P. J.; Freer, M.; Ashwood, N. I.; Bloxham, T.; Curtis, N.; Bohlen, H. G.; Dorsch, T.; Kokalova, Tz; Wheldon, C.; Catford, W. N.; Patterson, N. P.; Thomas, J. S.

    2010-03-01

    The 12C(13C, 9Be)16O reaction has been used to populate excited states in 16O. The 9Be nuclei were detected in a magnetic spectrometer and the 12C decay product of the recoiling excited 16O nucleus was detected in an array of silicon strip detectors. The large angular coverage of the strip detector array allowed the α-decay widths of the 14.66 MeV, 5-, and 16.275 MeV, 6+, states to be determined with good accuracy. The present results, together with earlier measurements, allow precise values for the branching ratios to be calculated: Ex(16O) = 14.66 MeV, Jπ = 5-, Γα0/Γ = 0.951 ± 0.049 and Γα1/Γ < 0.05; Ex(16O) = 16.275 MeV, Jπ = 6+, Γα0/Γ = 0.982 ± 0.048 and Γα1/Γ < 0.02.

  5. Probing the Locality of Excited States with Linear Algebra.

    PubMed

    Etienne, Thibaud

    2015-04-14

    This article reports a novel theoretical approach related to the analysis of molecular excited states. The strategy introduced here involves gathering two pieces of physical information, coming from Hilbert and direct space operations, into a general, unique quantum mechanical descriptor of electronic transitions' locality. Moreover, the projection of Hilbert and direct space-derived indices in an Argand plane delivers a straightforward way to visually probe the ability of a dye to undergo a long- or short-range charge-transfer. This information can be applied, for instance, to the analysis of the electronic response of families of dyes to light absorption by unveiling the trend of a given push-pull chromophore to increase the electronic cloud polarization magnitude of its main transition with respect to the size extension of its conjugated spacer. We finally demonstrate that all the quantities reported in this article can be reliably approximated by a linear algebraic derivation, based on the contraction of detachment/attachment density matrices from canonical to atomic space. This alternative derivation has the remarkable advantage of a very low computational cost with respect to the previously used numerical integrations, making fast and accurate characterization of large molecular systems' excited states easily affordable. PMID:26574379

  6. Probing the Locality of Excited States with Linear Algebra.

    PubMed

    Etienne, Thibaud

    2015-04-14

    This article reports a novel theoretical approach related to the analysis of molecular excited states. The strategy introduced here involves gathering two pieces of physical information, coming from Hilbert and direct space operations, into a general, unique quantum mechanical descriptor of electronic transitions' locality. Moreover, the projection of Hilbert and direct space-derived indices in an Argand plane delivers a straightforward way to visually probe the ability of a dye to undergo a long- or short-range charge-transfer. This information can be applied, for instance, to the analysis of the electronic response of families of dyes to light absorption by unveiling the trend of a given push-pull chromophore to increase the electronic cloud polarization magnitude of its main transition with respect to the size extension of its conjugated spacer. We finally demonstrate that all the quantities reported in this article can be reliably approximated by a linear algebraic derivation, based on the contraction of detachment/attachment density matrices from canonical to atomic space. This alternative derivation has the remarkable advantage of a very low computational cost with respect to the previously used numerical integrations, making fast and accurate characterization of large molecular systems' excited states easily affordable.

  7. Surface hopping investigation of benzophenone excited state dynamics.

    PubMed

    Favero, Lucilla; Granucci, Giovanni; Persico, Maurizio

    2016-04-21

    We present a simulation of the photodynamics of benzophenone for the first 20 ps after n →π* excitation, performed by trajectory surface hopping calculations with on-the-fly semiempirical determination of potential energy surfaces and electronic wavefunctions. Both the dynamic and spin-orbit couplings are taken into account, and time-resolved fluorescence emission is also simulated. The computed decay time of the S1 state is in agreement with experimental observations. The direct S1→ T1 intersystem crossing (ISC) accounts for about 2/3 of the S1 decay rate. The remaining 1/3 goes through T2 or higher triplets. The nonadiabatic transitions within the triplet manifold are much faster than ISC and keep the population of T1 at about 3/4 of the total triplet population, and that of the other states (mainly T2) at 1/4. Two internal coordinates are vibrationally active immediately after n →π* excitation: one is the C[double bond, length as m-dash]O stretching and the other one is a combination of the conrotatory torsion of phenyl rings and of bending involving the carbonyl C atom. The period of the torsion-bending mode coincides with oscillations in the time-resolved photoelectron spectra of Spighi et al. and substantially confirms their assignment. PMID:27031566

  8. Electronic excited States of polynucleotides: a study by electroabsorption spectroscopy.

    PubMed

    Krawczyk, Stanislaw; Luchowski, Rafal

    2007-02-01

    Electroabsorption spectra were obtained for single-stranded polynucleotides poly(U), poly(C), poly(A), and poly(G) in glycerol/water glass at low temperature, and the differences in permanent dipole moment (Deltamu) and polarizability (Deltaalpha) were estimated for several spectral ranges covering the lowest energy absorption band around 260 nm. In each spectral range, the electrooptical parameters associated with apparent features in the absorption spectrum exhibit distinct values representing either a dominant single transition or the resultant value for a group of a relatively narrow cluster of overlapping transitions. The estimated spacing in energy between electronic origins of these transitions is larger than the electronic coupling within the Coulombic interaction model which is usually adopted in computational studies. The electroabsorption data allow us to distinguish a weak electronic transition associated with a wing in polynucleotide absorption spectra, at an energy below the electronic origin in absorption spectra of monomeric nucleobases. In poly(C) and poly(G), these low-energy transitions are related to increased values of Deltamu and Deltaalpha, possibly indicating a weak involvement of charge resonance in the respective excited states. A model capable of explaining the origin of low-energy excited states, based on the interaction of pipi* and npi* transitions in neighboring bases, is introduced and briefly discussed on the grounds of point dipole interaction. PMID:17266277

  9. Excited state dynamics of thulium ions in yttrium aluminum garnets

    NASA Technical Reports Server (NTRS)

    Armagan, G.; Buoncristiani, A. M.; Dibartolo, B.

    1991-01-01

    The processes that take place in the excited states of a trivalent Thulium (Tm) ion in an Yttrium Aluminum Garnet (YAG) crystal, being relevant to the use of this system for laser applications, have been the object of several studies. We have reexamined this system focusing our attention on the dynamics of Tm following its excitation in the H-3(sub 4) level. Under these conditions the system relaxes through a cross-relaxation process. H-3(sub 4) yields F-3(sub 4), H-3(sub 6) yields F-3(sub 4), whose rate depends upon both the concentration of the Tm ion and the temperature of the crystal. The excitation spectrum obtained by monitoring the 1.8 micron emission of Tm (due to the F-3(sub 4) yields H-3(sub 6) transition) indicates an increase in the contribution to this emission from the H-3(sub 4) level relative to the H-3(sub 5) level as the Tm concentration increases; this shows the increased role played by the H-3(sub 4) level in pumping the infrared emission. Correspondingly, the duration of the luminescence originating in the H-3(sub 4) level is shortened as the concentration of Tm increases. The concentration quenching of this lifetime can be fit to a model which assumes that the cross-relaxation is due to a dipole-dipole interaction; from this fit, the intrinsic Tm lifetime in the absence of cross relaxation can be derived. We have used this lifetime to calculate the rate of the cross-relaxation process. We have evaluated this rate as a function of the temperature and found it to be fastest at 77 K. We have also calculated the microscopic interaction parameters for the cross-relaxation process by using two independent experimental features: (1) the time evolution of the emission from the H-3(sub 4) level; and (2) the spectral overlap between the H-3(sub 4) yields F-3(sub 4) emission and the H-3(sub 6) yields F-3(sub 4) absorption. We have also considered the migration of excitation among the Tm ions in the F-3(sub 4) level and calculated the relevant

  10. Excited state dynamics & optical control of molecular motors

    NASA Astrophysics Data System (ADS)

    Wiley, Ted; Sension, Roseanne

    2014-03-01

    Chiral overcrowded alkenes are likely candidates for light driven rotary molecular motors. At their core, these molecular motors are based on the chromophore stilbene, undergoing ultrafast cis/trans photoisomerization about their central double bond. Unlike stilbene, the photochemistry of molecular motors proceeds in one direction only. This unidirectional rotation is a result of helicity in the molecule induced by steric hindrance. However, the steric hindrance which ensures unidirectional excited state rotation, has the unfortunate consequence of producing large ground state barriers which dramatically decrease the overall rate of rotation. These molecular scale ultrafast motors have only recently been studied by ultrafast spectroscopy. Our lab has studied the photochemistry and photophysics of a ``first generation'' molecular motor with UV-visible transient absorption spectroscopy. We hope to use optical pulse shaping to enhance the efficiency and turnover rate of these molecular motors.

  11. Excitation gap of fractal quantum hall states in graphene

    NASA Astrophysics Data System (ADS)

    Luo, Wenchen; Chakraborty, Tapash

    2016-01-01

    In the presence of a magnetic field and an external periodic potential the Landau level spectrum of a two-dimensional electron gas exhibits a fractal pattern in the energy spectrum which is described as the Hofstadter’s butterfly. In this work, we develop a Hartree-Fock theory to deal with the electron-electron interaction in the Hofstadter’s butterfly state in a finite-size graphene with periodic boundary conditions, where we include both spin and valley degrees of freedom. We then treat the butterfly state as an electron crystal so that we could obtain the order parameters of the crystal in the momentum space and also in an infinite sample. A phase transition between the liquid phase and the fractal crystal phase can be observed. The excitation gaps obtained in the infinite sample is comparable to those in the finite-size study, and agree with a recent experimental observation.

  12. A benchmark study of electronic excitation energies, transition moments, and excited-state energy gradients on the nicotine molecule

    SciTech Connect

    Egidi, Franco Segado, Mireia; Barone, Vincenzo; Koch, Henrik; Cappelli, Chiara

    2014-12-14

    In this work, we report a comparative study of computed excitation energies, oscillator strengths, and excited-state energy gradients of (S)-nicotine, chosen as a test case, using multireference methods, coupled cluster singles and doubles, and methods based on time-dependent density functional theory. This system was chosen because its apparent simplicity hides a complex electronic structure, as several different types of valence excitations are possible, including n-π{sup *}, π-π{sup *}, and charge-transfer states, and in order to simulate its spectrum it is necessary to describe all of them consistently well by the chosen method.

  13. A benchmark study of electronic excitation energies, transition moments, and excited-state energy gradients on the nicotine molecule

    NASA Astrophysics Data System (ADS)

    Egidi, Franco; Segado, Mireia; Koch, Henrik; Cappelli, Chiara; Barone, Vincenzo

    2014-12-01

    In this work, we report a comparative study of computed excitation energies, oscillator strengths, and excited-state energy gradients of (S)-nicotine, chosen as a test case, using multireference methods, coupled cluster singles and doubles, and methods based on time-dependent density functional theory. This system was chosen because its apparent simplicity hides a complex electronic structure, as several different types of valence excitations are possible, including n-π*, π-π*, and charge-transfer states, and in order to simulate its spectrum it is necessary to describe all of them consistently well by the chosen method.

  14. Neutron decay widths of excited states of Be11

    NASA Astrophysics Data System (ADS)

    Haigh, P. J.; Freer, M.; Ashwood, N. I.; Bloxham, T.; Curtis, N.; McEwan, P.; Bohlen, H. G.; Dorsch, T.; Kokalova, Tz.; Schulz, Ch.; Wheldon, C.

    2009-01-01

    The two-neutron transfer reaction Be9(O16, O14)Be11[Be10 +n] has been used to measure the branching ratios for the neutron decay of excited states of Be11. The O14 ejectile was detected by a Q3D spectrometer at forward angles. The energies and angles of the Be10 fragments of the decaying Be11* recoil were measured in coincidence with the O14 ejectile using a double-sided silicon strip detector array at backward angles. This enabled a kinematic reconstruction of the reaction to be performed. Theoretical decay branch ratios were calculated using barrier penetrability factors and were compared to the measured ratios to provide information on the relative reduced widths of the states. The decay widths have been used to link states in Be11 with a common structure and structurally to states in the daughter nucleus Be10. The 3/2-8.82-MeV state was identified as a candidate for a molecular band head.

  15. Ultrafast electronic relaxation of excited state vitamin B 12 in the gas phase

    NASA Astrophysics Data System (ADS)

    Shafizadeh, Niloufar; Poisson, Lionel; Soep, Benoıˆt

    2008-06-01

    The time evolution of electronically excited vitamin B 12 (cyanocobalamin) has been observed for the first time in the gas phase. It reveals an ultrafast decay to a state corresponding to metal excitation. This decay is interpreted as resulting from a ring to metal electron transfer. This opens the observation of the excited state of other complex biomimetic systems in the gas phase, the key to the characterisation of their complex evolution through excited electronic states.

  16. Lowest singlet excited state and spectroscopy of α-carotene

    NASA Astrophysics Data System (ADS)

    Itoh, Takao

    2011-03-01

    Emission, excitation and absorption spectra of α-carotene have been measured in solvents with different polarizabilities. It is shown that in highly-polarized solvents α-carotene emits weak fluorescence from the S 1( π, π∗) state with the fluorescence origin observed at 14 800 ± 200 cm -1. The relative S 1/S 2 fluorescence intensity ratio tends to increase with increasing solvent polarizability or decreasing the S 1-S 2 energy separation. The obtained spectroscopic data include the Raman spectrum of α-carotene along with the vibrational analyses of the Raman spectrum based on the DFT calculation at the B3LYP/6-31G(d,p) level.

  17. Measurement of Atomic Oscillator Strength Distribution from the Excited States

    SciTech Connect

    Hussain, Shahid; Saleem, M.; Baig, M. A.

    2008-10-22

    Saturation technique has been employed to measure the oscillator strength distribution in spectra of helium lithium using an electrical discharge cell a thermionic diode ion detector respectively. The photoabsorption cross sections in the discrete or bound region (commonly known as f-values) have been determined form the Rydberg series accessed from a particular excited state calibrating it with the absolute value of the photoionization cross section measured at the ionization threshold. The extracted discrete f-values merge into the oscillator strength densities, estimated from the measured photoionization cross sections at different photon energies above the first ionization threshold. The experimental data on helium and lithium show continuity between the discrete and the continuous oscillator strengths across the ionization threshold.

  18. Chimera states and excitation waves in networks with complex topologies

    NASA Astrophysics Data System (ADS)

    Schöll, Eckehard

    2016-06-01

    Chimera patterns, which consist of coexisting spatial domains of coherent (synchronized) and incoherent (desyn- chronized) dynamics are studied in networks of FitzHugh-Nagumo systems with complex topologies. To test the robustness of chimera patterns with respect to changes in the structure of the network, we study the following network topologies: Regular ring topology with R nearest neigbors coupled to each side, small-world topology with additional long-range random links, and a hierarchical geometry in the connectivity matrix. We find that chimera states are generally robust with respect to these perturbations, but qualitative changes of the chimera patterns in form of nested coherent and incoherent regions can be induced by a hierarchical topology. The suppression of propagating excitation waves by a small-world topology is also reviewed.

  19. Entanglement thermodynamics for an excited state of Lifshitz system

    NASA Astrophysics Data System (ADS)

    Chakraborty, Somdeb; Dey, Parijat; Karar, Sourav; Roy, Shibaji

    2015-04-01

    A class of (2+1)-dimensional quantum many body system characterized by an anisotropic scaling symmetry (Lifshitz symmetry) near their quantum critical point can be described by a (3+1)-dimensional dual gravity theory with negative cosmological constant along with a massive vector field, where the scaling symmetry is realized by the metric as an isometry. We calculate the entanglement entropy of an excited state of such a system holographically, i.e., from the asymptotic perturbation of the gravity dual using the prescription of Ryu and Takayanagi, when the subsystem is sufficiently small. With suitable identifications, we show that this entanglement entropy satisfies an energy conservation relation analogous to the first law of thermodynamics. The non-trivial massive vector field here plays a crucial role and contributes to an additional term in the energy relation.

  20. Theoretical description of excited state dynamics in nanostructures

    NASA Astrophysics Data System (ADS)

    Rubio, Angel

    2009-03-01

    There has been much progress in the synthesis and characterization of nanostructures however, there remain immense challenges in understanding their properties and interactions with external probes in order to realize their tremendous potential for applications (molecular electronics, nanoscale opto-electronic devices, light harvesting and emitting nanostructures). We will review the recent implementations of TDDFT to study the optical absorption of biological chromophores, one-dimensional polymers and layered materials. In particular we will show the effect of electron-hole attraction in those systems. Applications to the optical properties of solvated nanostructures as well as excited state dynamics in some organic molecules will be used as text cases to illustrate the performance of the approach. Work done in collaboration with A. Castro, M. Marques, X. Andrade, J.L Alonso, Pablo Echenique, L. Wirtz, A. Marini, M. Gruning, C. Rozzi, D. Varsano and E.K.U. Gross.

  1. Theoretical study on the excited states of HCN

    SciTech Connect

    Nayak, Malaya K.; Chaudhuri, Rajat K.; Krishnamachari, S.N.L.G.

    2005-05-08

    In the flash-photolysis of oxazole, iso-oxazole, and thiozole a transient band system was observed in the region 2500-3050 A. This band system was attributed to a meta-stable form of HCN, i.e., either HNC or triplet HCN. Theoretical investigations have been carried out on the ground and excited states of HCN to characterize this and other experimentally observed transitions. The predicted geometries are compared with the experiment and earlier theoretical calculations. The present calculations show that the band system in the region 2500-3050 A corresponds to the transition 4 {sup 3}-A{sup '}<{sup -}1 {sup 3}-A{sup '} of HCN.

  2. UV excited-state photoresponse of biochromophore negative ions.

    PubMed

    Bochenkova, Anastasia V; Klærke, Benedikte; Rahbek, Dennis B; Rajput, Jyoti; Toker, Yoni; Andersen, Lars H

    2014-09-01

    Members of the green fluorescent protein (GFP) family may undergo irreversible phototransformation upon irradiation with UV light. This provides clear evidence for the importance of the higher-energy photophysics of the chromophore, which remains essentially unexplored. By using time-resolved action and photoelectron spectroscopy together with high-level electronic structure theory, we directly probe and identify higher electronically excited singlet states of the isolated para- and meta-chromophore anions of GFP. These molecular resonances are found to serve as a doorway for very efficient electron detachment in the gas phase. Inside the protein, this band is found to be resonant with the quasicontinuum of a solvated electron, thus enhancing electron transfer from the GFP to the solvent. This suggests a photophysical pathway for photoconversion of the protein, where GFP resonant photooxidation in solution triggers radical redox reactions inside these proteins. PMID:25044707

  3. Theoretical studies of excited state 1,3 dipolar cycloadditions

    NASA Astrophysics Data System (ADS)

    Belluccci, Michael A.

    The 1,3 dipolar photocycloaddition reaction between 3-hydroxy-4',5,7-trimethoxyflavone (3-HTMF) and methyl cinnamate is investigated in this work. Since its inception in 2004 [JACS, 124, 13260 (2004)], this reaction remains at the forefront in the synthetic design of the rocaglamide natural products. The reaction is multi-faceted in that it involves multiple excited states and is contingent upon excited state intramolecular proton transfer (ESIPT) in 3-HTMF. Given the complexity of the reaction, there remain many questions regarding the underlying mechanism. Consequently, throughout this work we investigate the mechanism of the reaction along with a number of other properties that directly influence it. To investigate the photocycloaddition reaction, we began by studying the effects of different solvent environments on the ESIPT reaction in 3-hydroxyflavone since this underlying reaction is sensitive to the solvent environment and directly influences the cycloaddition. To study the ESIPT reaction, we developed a parallel multi-level genetic program to fit accurate empirical valence bond (EVB) potentials to ab initio data. We found that simulations with our EVB potentials accurately reproduced experimentally determined reaction rates, fluorescence spectra, and vibrational frequency spectra in all solvents. Furthermore, we found that the ultrafast ESIPT process results from a combination of ballistic transfer and intramolecular vibrational redistribution. To investigate the cycloaddition reaction mechanism, we utilized the string method to obtain minimum energy paths on the ab initio potential. These calculations demonstrated that the reaction can proceed through formation of an exciplex in the S1 state, followed by a non-adiabatic transition to the ground state. In addition, we investigated the enantioselective catalysis of the reaction using alpha,alpha,alpha',alpha'-tetraaryl-1,3-dioxolan-4,5-dimethanol alcohol (TADDOL). We found that TADDOL lowered the energy

  4. Pseudopotential Calculation of the Excited States of Semiconductor Quantum Dots

    NASA Astrophysics Data System (ADS)

    Williamson, Andrew; Wang, Lin-Wang; Fu, Hiauxiang; Zunger, Alex

    1998-03-01

    We present the results of our pseudopotential calculations of up to 10 single-exciton states in free standing InP, InAs and CdSe quantum dots with diameters ranging from 10 to 50ÅIn the first step we solve for ≈20-40 single particle hole and electron states using a screened atomic pseudopotential Hamiltonian[1], solved within a plane wave basis using the Folded Spectrum Method[2]. In the second step, we calculate the electron-hole Coulomb energy[3] and the dipole transition probability for each of the ≈1000 possible single particle excitations. We present a comparison of the size scaling of the peaks in absorption and emission spectra obtained in our calculations with those from recent experiments and those of the effective mass based, k.p method. We also compare pseudopotential and k.p predictions of the character of the initial and final single particle states associated with each of these emission peaks. [1] J. Kim, A.J. Williamson, L.W. Wang, S.H-. Wei and A. Zunger, submitted to Phys. Rev. B [2] L. W. Wang and A. Zunger, J. Chem. Phys. 100, 2394 (1994). [3] A. Franceschetti and A. Zunger, Phys. Rev. Lett. 78, 915 (1997). *Supported under BES/OER/DMS contract No. DE---AC36---83CH10093

  5. Transfer matrices and excitations with matrix product states

    NASA Astrophysics Data System (ADS)

    Zauner, V.; Draxler, D.; Vanderstraeten, L.; Degroote, M.; Haegeman, J.; Rams, M. M.; Stojevic, V.; Schuch, N.; Verstraete, F.

    2015-05-01

    We use the formalism of tensor network states to investigate the relation between static correlation functions in the ground state of local quantum many-body Hamiltonians and the dispersion relations of the corresponding low-energy excitations. In particular, we show that the matrix product state transfer matrix (MPS-TM)—a central object in the computation of static correlation functions—provides important information about the location and magnitude of the minima of the low-energy dispersion relation(s), and we present supporting numerical data for one-dimensional lattice and continuum models as well as two-dimensional lattice models on a cylinder. We elaborate on the peculiar structure of the MPS-TM’s eigenspectrum and give several arguments for the close relation between the structure of the low-energy spectrum of the system and the form of the static correlation functions. Finally, we discuss how the MPS-TM connects to the exact quantum transfer matrix of the model at zero temperature. We present a renormalization group argument for obtaining finite bond dimension approximations of the MPS, which allows one to reinterpret variational MPS techniques (such as the density matrix renormalization group) as an application of Wilson’s numerical renormalization group along the virtual (imaginary time) dimension of the system.

  6. Excited states of the 5-chlorophyll photosystem II reaction center

    SciTech Connect

    Jankowiak, R.; Raetsep, M.; Picorel, R.; Seibert, M.; Small, G.J.

    1999-11-04

    Results of 4.2 K hole burning, chemical reduction (sodium dithionite, in dark and with illumination), and oxidation (ferricyanide) experiments are reported for the isolated PS II reaction center containing five chlorophyll (Chl) molecules (RC-5). Q{sub y} states at 679.6 and 668.3 nm are identified as being highly localized on pheophytin a of the D{sub 1} branch (Pheo{sub 1}) and pheophytin a of the D{sub 2} branch (Pheo{sub 2}), respectively. The Pheo{sub 1}-Q{sub x} and Pheo{sub 2}-Q{sub x} transitions were found to lie on the low and high energy sides of the single Pheo-Q{sub x} absorption band, at 544.4 and 541.2 nm, respectively. The Q{sub y} band of the 684 nm absorbing Chl, which is more apparent in absorption in RC-5 than in RC-6 samples, is assigned to the peripheral Chl on the D{sub 1} side. The results are consistent with that peripheral Chl being Chl{sub z}. The results indicate that P680, the primary electron donor, is the main acceptor for energy transfer from the Pheo{sub 1}-Q{sub y} state and that excitation energy transfer from the Pheo{sub 1}-Q{sub y} state and P680* to the 684 nm Chl is inefficient. It is concluded that the procedure used to prepare RC-5 has only a small effect on the energies of the Q{sub y} states associated with the core cofactors of the 6-Chl RC as well as the 684 nm Chl. Implications of the results for the multimer model are considered. In that model the Q{sub y}-states of the core are significantly delocalized over several cofactors. The results presented provide no support for this model.

  7. Microwave Spectroscopy of the Excited Vibrational States of Methanol

    NASA Astrophysics Data System (ADS)

    Pearson, John; Daly, Adam M.; Bermúdez, Celina

    2015-06-01

    Methanol is the simplest molecule with a three-fold internal rotation and the observation of its νb{8} band served the primary catalyst for the development of internal rotation theory(a,b). The 75 subsequent years of investigation into the νb{8} band region have yielded a large number assignments, numerous high precision energy levels and a great deal of insight into the coupling of νb{t}=3 & 4 with νb{8}, νb{7}, νb{11} and other nearby states(c). In spite of this progress numerous assignment mysteries persist, the origin of almost half the far infrared laser lines remain unknown and all attempts to model the region quantum mechanically have had very limited success. The C3V internal rotation Hamiltonian has successfully modeled the νb{t}=0,1 & 2 states of methanol and other internal rotors(d). However, successful modeling of the coupling between torsional bath states and excited small amplitude motion remains problematic and coupling of multiple interacting excited small amplitude vibrations featuring large amplitude motions remains almost completely unexplored. Before such modeling can be attempted, identifying the remaining low lying levels of νb{7} and νb{11} is necessary. We present an investigation into the microwave spectrum of νb{7}, νb{8} and νb{11} along with the underlying torsional bath states in νb{t}=3 and νb{t}= 4. (a) A. Borden, E.F. Barker J. Chem. Phys., 6, 553 (1938). (b) J. S. Koehler and D. M. Dennison, Phys. Rev. 57, 1006 (1940). (c) R. M. Lees, Li-Hong Xu, J. W. C. Johns, B. P. Winnewisser, and M. Lock, J. Mol. Spectrosc. 243, 168 (2007). (d) L.-H. Xu, J. Fisher, R.M. Lees, H.Y. Shi, J.T. Hougen, J.C. Pearson, B.J. Drouin, G.A. Blake, R. Braakman J. Mol. Spectrosc., 251, 305 (2008).

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

    SciTech Connect

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

    2014-05-14

    We show that femtosecond stimulated Raman spectroscopy can record excited-state spectra in the absence of actinic excitation, if the Raman pump is in resonance with an electronic transition. The approach is illustrated by recording S{sub 1} and S{sub 0} spectra of trans-azobenzene in n-hexane. The S{sub 1} spectra were also measured conventionally, upon nπ* (S{sub 0} → S{sub 1}) actinic excitation. The results are discussed and compared to earlier reports.

  9. Stability of quantum-dot excited-state laser emission under simultaneous ground-state perturbation

    SciTech Connect

    Kaptan, Y. Herzog, B.; Schöps, O.; Kolarczik, M.; Woggon, U.; Owschimikow, N.; Röhm, A.; Lingnau, B.; Lüdge, K.; Schmeckebier, H.; Arsenijević, D.; Bimberg, D.; Mikhelashvili, V.; Eisenstein, G.

    2014-11-10

    The impact of ground state amplification on the laser emission of In(Ga)As quantum dot excited state lasers is studied in time-resolved experiments. We find that a depopulation of the quantum dot ground state is followed by a drop in excited state lasing intensity. The magnitude of the drop is strongly dependent on the wavelength of the depletion pulse and the applied injection current. Numerical simulations based on laser rate equations reproduce the experimental results and explain the wavelength dependence by the different dynamics in lasing and non-lasing sub-ensembles within the inhomogeneously broadened quantum dots. At high injection levels, the observed response even upon perturbation of the lasing sub-ensemble is small and followed by a fast recovery, thus supporting the capacity of fast modulation in dual-state devices.

  10. Coherence, Energy and Charge Transfers in De-Excitation Pathways of Electronic Excited State of Biomolecules in Photosynthesis

    NASA Astrophysics Data System (ADS)

    Bohr, Henrik G.; Malik, F. Bary

    2013-11-01

    The observed multiple de-excitation pathways of photo-absorbed electronic excited state in the peridinin-chlorophyll complex, involving both energy and charge transfers among its constituents, are analyzed using the bio-Auger (B-A) theory. It is also shown that the usually used Förster-Dexter theory, which does not allow for charge transfer, is a special case of B-A theory. The latter could, under appropriate circumstances, lead to excimers.

  11. A Computational Method for Determining the Equilibrium Composition and Product Temperature in a LH2/LOX Combustor

    NASA Technical Reports Server (NTRS)

    Sozen, Mehmet

    2003-01-01

    In what follows, the model used for combustion of liquid hydrogen (LH2) with liquid oxygen (LOX) using chemical equilibrium assumption, and the novel computational method developed for determining the equilibrium composition and temperature of the combustion products by application of the first and second laws of thermodynamics will be described. The modular FORTRAN code developed as a subroutine that can be incorporated into any flow network code with little effort has been successfully implemented in GFSSP as the preliminary runs indicate. The code provides capability of modeling the heat transfer rate to the coolants for parametric analysis in system design.

  12. Excited State Dynamics of 7-AZAINDOLE Homodimer in Frozen Nitrogen Matrix

    NASA Astrophysics Data System (ADS)

    Mukherjee, Moitrayee; Bandyopadhyay, Biman; Karmakar, Shreetama; Chakraborty, Tapas

    2011-06-01

    In a fluid medium (liquid or gas), the doubly hydrogen bonded dimer of 7-azaindole (7AI) undergoes tautomerization via simultaneous exchange of two H-atoms/protons between the two moieties upon UV excitation to lowest excited singlet state. The excited dimer emits exclusively visible fluorescence from tautomeric configuration, and no UV fluorescence is detected from the locally excited state. We show here for the first time that this generic excited state dynamics of 7AI dimer is totally altered if the species is synthesized and confined in frozen nitrogen at 8 K. The dimer has been found to emit only from the locally excited state, and the photophysical channel leading to excited state tautomerization is completely blocked. The formation of the centrosymmetric dimer in nitrogen matrix is ensured by recording the FTIR spectrum of the dimer before initiating the photophysical measurements. The details of our findings and interpretation of the measured data will be presented in the talk.

  13. Excited-State Dynamics in Colloidal Semiconductor Nanocrystals.

    PubMed

    Rabouw, Freddy T; de Mello Donega, Celso

    2016-10-01

    Colloidal semiconductor nanocrystals have attracted continuous worldwide interest over the last three decades owing to their remarkable and unique size- and shape-, dependent properties. The colloidal nature of these nanomaterials allows one to take full advantage of nanoscale effects to tailor their optoelectronic and physical-chemical properties, yielding materials that combine size-, shape-, and composition-dependent properties with easy surface manipulation and solution processing. These features have turned the study of colloidal semiconductor nanocrystals into a dynamic and multidisciplinary research field, with fascinating fundamental challenges and dazzling application prospects. This review focuses on the excited-state dynamics in these intriguing nanomaterials, covering a range of different relaxation mechanisms that span over 15 orders of magnitude, from a few femtoseconds to a few seconds after photoexcitation. In addition to reviewing the state of the art and highlighting the essential concepts in the field, we also discuss the relevance of the different relaxation processes to a number of potential applications, such as photovoltaics and LEDs. The fundamental physical and chemical principles needed to control and understand the properties of colloidal semiconductor nanocrystals are also addressed. PMID:27573500

  14. Investigation of excited 0+ states populated in the 162 Er (p,t) reaction

    NASA Astrophysics Data System (ADS)

    Burbadge, C.; Bildstein, V.; Diaz Varela, A.; Dunlop, M.; Dunlop, R.; Garrett, P. E.; Jamieson, D. S.; Kisliuk, D.; Leach, K. G.; Loranger, J.; Maclean, A.; Radich, A.; Rand, E.; Svensson, C. E.; Ball, G. C.; Triambak, S.; Faestermann, T.; Hertenberger, R.; Wirth, H.-F.

    2015-10-01

    A continuing challenge in nuclear structure physics is the determination of the nature of low-lying excited 0+ states. Various approaches have been implemented to interpret the occurence of these states, such as vibrational excitations in β and γ phonons or pairing excitations. One of the difficulties, however, in resolving the nature of these states is that there is a paucity of data; even the first excited state, 02+,is not always known. Direct two-neutron transfer reactions are a useful tool for locating and investigating the nature of excited 0+ states in well-deformed nuclei. Using the Q3D spectrograph at the Maier-Leibnitz Laboratory, the N = 92 nucleus 160Er was studied via (p , t) reactions with a highly-enriched 162Er target. Strong population of the 02+state was observed with large cross sections greater than any other excited 0+ state. Preliminary results will be presented.

  15. Ultrafast time-resolved spectroscopy of the light-harvesting complex 2 (LH2) from the photosynthetic bacterium Thermochromatium tepidum

    SciTech Connect

    Niedzwiedzki, Dariusz M.; Fuciman, Marcel; Kobayashi, Masayuki; Frank, Harry A.; Blankenship, Robert E.

    2011-10-08

    The light-harvesting complex 2 from the thermophilic purple bacterium Thermochromatium tepidum was purified and studied by steady-state absorption and fluorescence, sub-nanosecond-time-resolved fluorescence and femtosecond time-resolved transient absorption spectroscopy. The measurements were performed at room temperature and at 10 K. The combination of both ultrafast and steady-state optical spectroscopy methods at ambient and cryogenic temperatures allowed the detailed study of carotenoid (Car)-to-bacteriochlorophyll (BChl) as well BChl-to-BChl excitation energy transfer in the complex. The studies show that the dominant Cars rhodopin (N = 11) and spirilloxanthin (N = 13) do not play a significant role as supportive energy donors for BChl a. This is related with their photophysical properties regulated by long π-electron conjugation. On the other hand, such properties favor some of the Cars, particularly spirilloxanthin (N = 13) to play the role of the direct quencher of the excited singlet state of BChl.

  16. Linear energy relationships in ground state proton transfer and excited state proton-coupled electron transfer.

    PubMed

    Gamiz-Hernandez, Ana P; Magomedov, Artiom; Hummer, Gerhard; Kaila, Ville R I

    2015-02-12

    Proton-coupled electron transfer (PCET) processes are elementary chemical reactions involved in a broad range of radical and redox reactions. Elucidating fundamental PCET reaction mechanisms are thus of central importance for chemical and biochemical research. Here we use quantum chemical density functional theory (DFT), time-dependent density functional theory (TDDFT), and the algebraic diagrammatic-construction through second-order (ADC(2)) to study the mechanism, thermodynamic driving force effects, and reaction barriers of both ground state proton transfer (pT) and photoinduced proton-coupled electron transfer (PCET) between nitrosylated phenyl-phenol compounds and hydrogen-bonded t-butylamine as an external base. We show that the obtained reaction barriers for the ground state pT reactions depend linearly on the thermodynamic driving force, with a Brønsted slope of 1 or 0. Photoexcitation leads to a PCET reaction, for which we find that the excited state reaction barrier depends on the thermodynamic driving force with a Brønsted slope of 1/2. To support the mechanistic picture arising from the static potential energy surfaces, we perform additional molecular dynamics simulations on the excited state energy surface, in which we observe a spontaneous PCET between the donor and the acceptor groups. Our findings suggest that a Brønsted analysis may distinguish the ground state pT and excited state PCET processes.

  17. Spacecraft attitude impacts on COLD-SAT non-vacuum jacketed LH2 supply tank thermal performance

    NASA Technical Reports Server (NTRS)

    Arif, Hugh

    1990-01-01

    The Cryogenic On-Orbit Liquid Depot - Storage, Acquisition and Transfer (COLD-SAT) spacecraft will be launched into low earth orbit to perform fluid management experiments on the behavior of subcritical liquid hydrogen (LH2). For determining the optimum on-orbit attitude for the COLD-SAT satellite, a comparative analytical study was performed to determine the thermal impacts of spacecraft attitude on the performance of the COLD-SAT non-vacuum jacketed LH2 supply tank. Tank thermal performance was quantified by total conductive and radiative heat leakage into the pressure vessel due to the absorbed solar, earth albedo and infra-red on-orbit fluxes, and also by the uniformity of the variation of this leakage on the vessel surface area. Geometric and thermal analysis math models were developed for the spacecraft and the tank as part of this analysis, based on their individual thermal/structural designs. Two quasi-inertial spacecraft attitudes were investigated and their effects on the tank performance compared. The results are one of the criteria by which the spacecraft orientation in orbit was selected for the in-house NASA Lewis Research Center design.

  18. Spacecraft attitude impacts on COLD-SAT non-vacuum jacketed LH2 supply tank thermal performance

    NASA Technical Reports Server (NTRS)

    Arif, Hugh

    1990-01-01

    The Cryogenic On-Orbit Liquid Depot - Storage, Acquisition and Transfer (COLD-SAT) spacecraft will be launched into low earth orbit to perform fluid management experiments on the behavior of subcritical liquid hydrogen (LH2). For determining the optimum on-orbit attitude for the COLD-SAT satellite, a comparative analytical study was performed to determine the thermal impacts of spacecraft attitude on the performance of the COLD-SAT non-vacuum jacketed LH2 supply tank. Tank thermal performance was quantitied by total conductive and radiative heat leakage into the pressure vessel due to the absorbed solar, earth albedo and infra-red on-orbit fluxes, and also by the uniformity of the variation of this leakage on the vessel surface area. Geometric and thermal analysis math models were developed for the spacecraft and the tank as part of this analysis, based on their individual thermal/structural designs. Two quasi-inertial spacecraft attitudes were investigated and their effects on the tank performance compared. The results are one of the criteria by which the spacecraft orientation in orbit was selected for the in-house NASA Lewis Research Center design.

  19. Navier-Stokes computations with finite-rate chemistry for LO2/LH2 rocket engine plume flow studies

    NASA Technical Reports Server (NTRS)

    Dougherty, N. Sam; Liu, Baw-Lin

    1991-01-01

    Computational fluid dynamics methods have been developed and applied to Space Shuttle Main Engine LO2/LH2 plume flow simulation/analysis of airloading and convective base heating effects on the vehicle at high flight velocities and altitudes. New methods are described which were applied to the simulation of a Return-to-Launch-Site abort where the vehicle would fly briefly at negative angles of attack into its own plume. A simplified two-perfect-gases-mixing approach is used where one gas is the plume and the other is air at 180-deg and 135-deg flight angle of attack. Related research has resulted in real gas multiple-plume interaction methods with finite-rate chemistry described herein which are applied to the same high-altitude-flight conditions of 0 deg angle of attack. Continuing research plans are to study Orbiter wake/plume flows at several Mach numbers and altitudes during ascent and then to merge this model with the Shuttle 'nose-to-tail' aerodynamic and SRB plume models for an overall 'nose-to-plume' capability. These new methods are also applicable to future launch vehicles using clustered-engine LO2/LH2 propulsion.

  20. TDDFT study on the excited-state proton transfer of 8-hydroxyquinoline: Key role of the excited-state hydrogen-bond strengthening

    NASA Astrophysics Data System (ADS)

    Lan, Sheng-Cheng; Liu, Yu-Hui

    2015-03-01

    Density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations have been employed to study the excited-state intramolecular proton transfer (ESIPT) reaction of 8-hydroxyquinoline (8HQ). Infrared spectra of 8HQ in both the ground and the lowest singlet excited states have been calculated, revealing a red-shift of the hydroxyl group (-OH) stretching band in the excited state. Hence, the intramolecular hydrogen bond (O-H···N) in 8HQ would be significantly strengthened upon photo-excitation to the S1 state. As the intramolecular proton-transfer reaction occurs through hydrogen bonding, the ESIPT reaction of 8HQ is effectively facilitated by strengthening of the electronic excited-state hydrogen bond (O-H···N). As a result, the intramolecular proton-transfer reaction would occur on an ultrafast timescale with a negligible barrier in the calculated potential energy curve for the ESIPT reaction. Therefore, although the intramolecular proton-transfer reaction is not favorable in the ground state, the ESIPT process is feasible in the excited state. Finally, we have identified that radiationless deactivation via internal conversion (IC) becomes the main dissipative channel for 8HQ by analyzing the energy gaps between the S1 and S0 states for the enol and keto forms.

  1. TDDFT study on the excited-state proton transfer of 8-hydroxyquinoline: key role of the excited-state hydrogen-bond strengthening.

    PubMed

    Lan, Sheng-Cheng; Liu, Yu-Hui

    2015-03-15

    Density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations have been employed to study the excited-state intramolecular proton transfer (ESIPT) reaction of 8-hydroxyquinoline (8HQ). Infrared spectra of 8HQ in both the ground and the lowest singlet excited states have been calculated, revealing a red-shift of the hydroxyl group (-OH) stretching band in the excited state. Hence, the intramolecular hydrogen bond (O-H···N) in 8HQ would be significantly strengthened upon photo-excitation to the S1 state. As the intramolecular proton-transfer reaction occurs through hydrogen bonding, the ESIPT reaction of 8HQ is effectively facilitated by strengthening of the electronic excited-state hydrogen bond (O-H···N). As a result, the intramolecular proton-transfer reaction would occur on an ultrafast timescale with a negligible barrier in the calculated potential energy curve for the ESIPT reaction. Therefore, although the intramolecular proton-transfer reaction is not favorable in the ground state, the ESIPT process is feasible in the excited state. Finally, we have identified that radiationless deactivation via internal conversion (IC) becomes the main dissipative channel for 8HQ by analyzing the energy gaps between the S1 and S0 states for the enol and keto forms.

  2. Synthetic control of excited states. Nonchromophoric ligand variations in polypyridyl complexes of osmium(II)

    SciTech Connect

    Kober, E.M.; Marshall, J.L.; Dressick, W.J.; Sullivan, B.P.; Caspar, J.V.; Meyer, T.J.

    1985-08-28

    Two themes are explored with regard to the properties of the metal to ligand charge-transfer (MLCT) excited states of Os(II). For a series of Os(II) complexes it is shown that the MLCT excited states undergo facile oxidative or reductive quenching. Excited-state redox potentials have been estimated by both kinetic quenching and spectroscopic techniques for excited-state oxidative couples and excited-state reductive couples. The second theme, the manipulation of excited-state properties by synthetic changes, follows from a consideration of these factors that dictate excited-state redox potentials. It is shown that in the series (phen)OsL/sub 4//sup 2 +/ (L = pyridine, CH/sub 3/CN, PR/sub 3/, AsR/sub 3/, ... and phen = 1,10-phenanthroline) where the metal-ligand basis for the MLCT chromophore remains the same and variations are made in the nonchromophoric ligand, emission energies, excited-state redox potentials, and radiative and nonradiative rate constants all vary systematically with the potential of the ground-state Os(III/II) couple. The results show that it is possible through synthetic changes to control excited-state properties in a systematical way. 37 references, 6 figures, 5 tables.

  3. The Structure of the Nucleon and it's Excited States

    SciTech Connect

    1995-02-20

    The past year has been an exciting and productive one for particle physics research at Abilene Christian University. The thrust of our experimental investigations is the study of the nucleon and its excited states. Laboratories where these investigations are presently being conducted are the AGS at Brookhaven, Fermilab and LAMPF. Some analysis of the data for experiments at the Petersburg Nuclear Physics Institute (Gatchina, Russia) is still in progress. Scheduling of activities at different laboratories inevitably leads to occasional conflicts. This likelihood is increased by the present budget uncertainties at the laboratories that make long-term scheduling difficult. For the most part, the investigators have been able to avoid such conflicts. Only one experiment received beam time in 1994 (E890 at the AGS). The situation for 1995-1996 also appears manageable at this point. E890 and another AGS experiment (E909) will run through May, 1995. El 178 at LAMPF is presently scheduled for August/September 1995. E866 at Fermilab is scheduled to start in Spring/Summer 1996. Undergraduate student involvement has been a key element in this research contract since its inception. Summer students participated at all of the above laboratories in 1994 and the same is planned in 1995. A transition to greater involvement by graduate students will provide cohesiveness to ACU involvement at a given laboratory and full-time on-site involvement in the longer running experiments at FNAL and BNL. Funds to support a full-time graduate student are requested this year. Finally, collaboration by Russian, Croatian and Bosnian scientists has proven to be mutually beneficial to these experimental programs and to the overall programs at the institutions involved. Past support has been augmented by other grants from government agencies and from the Research Council at Abilene Christian University. Additional funds are requested in this renewal to enable more programmatic support for these

  4. Coherence in the B800 Ring of Purple Bacteria LH2

    NASA Astrophysics Data System (ADS)

    Cheng, Y. C.; Silbey, R. J.

    2006-01-01

    We study the quantum coherence in the B800 ring and how it affects the dynamics of excitation energy transfer (EET) in photo-synthetic light-harvesting systems. From an analysis of the spectrum, we determine the disorder parameters for the B800 ring and show that the relatively weak electronic coupling between B800 pigments subtly changes the dynamics of EET and improves the uniformity and robustness of B800→B850 EET at room temperature, an example of how a multichromophoric assembly can exploit coherence to optimize the efficiency of photosynthesis. A molecular-level description for the dynamics of EET in the light-harvesting system may prove useful for understanding other nanoscale molecular assemblies and designing efficient nanoscale optical devices.

  5. Excited state absorption spectrum of chlorophyll a obtained with white-light continuum.

    PubMed

    De Boni, L; Correa, D S; Pavinatto, F J; dos Santos, D S; Mendonça, C R

    2007-04-28

    The study of excited state properties of chlorophyll a is a subject of foremost interest, given that it plays important roles in biological process and has also been proposed for applications in photonics. This work reports on the excited state absorption spectrum of chlorophyll a solution from 460 to 700 nm, obtained through the white-light continuum Z-scan technique. Saturation of absorption was observed due to the ground state depletion, induced by the white-light continuum region that is resonant with the Q band of chlorophyll a. The authors also observed reverse saturation of absorption related to the excitation from the first excited state to a higher energy level for wavelengths below 640 nm. An energy-level diagram, based on the electronic states of chlorophyll a, was employed to interpret their results, revealing that more states than the ones related to the Q and B bands participate in the excited state absorption of this molecule.

  6. The Evolution of Utilizing Manual Throttles to Avoid Excessively Low LH2 NPSP at the SSME Inlet

    NASA Technical Reports Server (NTRS)

    Henfling, Rick

    2011-01-01

    In the late 1970s, years before the Space Shuttle flew its maiden voyage, it was understood low liquid hydrogen (LH2) Net Positive Suction Pressure (NPSP) at the inlet to the Space Shuttle Main Engine (SSME) could have adverse effects on engine operation. A number of failures within both the External Tank (ET) and the Orbiter Main Propulsion System (MPS) could result in a low LH2 NPSP condition, which at extremely low levels can result in cavitation of SSME turbomachinery. Operational workarounds were developed to take advantage of the onboard crew s ability to manually throttle down the SSMEs (via the Pilot s Speedbrake/Throttle Controller), which alleviated the low LH2 NPSP condition. Manually throttling the SSME to a lower power level resulted in an increase in NPSP, mainly due to the reduction in frictional flow losses while at the lower throttle setting. Early in the Space Shuttle Program s history, the relevant Flight Rule for the Booster flight controllers in Mission Control did not distinguish between ET and Orbiter MPS failures and the same crew action was taken for both. However, after a review of all Booster operational techniques following the Challenger disaster in the late 1980s, it was determined manually throttling the SSME to a lower power was only effective for Orbiter MPS failures and the Flight Rule was updated to reflect this change. The Flight Rule and associated crew actions initially called for a single throttle step to minimum power level when a low threshold for NPSP was met. As engineers refined their understanding of the NPSP requirements for the SSME (through a robust testing program), the operational techniques evolved to take advantage of the additional capabilities. This paper will examine the evolution of the Flight rule and associated procedure and how increases in knowledge about the SSME and the Space Shuttle vehicle as a whole have helped shape their development. What once was a single throttle step when NPSP decreased to a

  7. The Evolution of Utilizing Manual Throttling to Avoid Excessively Low LH2 NPSP at the SSME Inlet

    NASA Technical Reports Server (NTRS)

    Henfling, Rick

    2010-01-01

    In the late 1970s, years before the Space Shuttle flew its maiden voyage, it was understood low liquid hydrogen (LH2) Net Positive Suction Pressure (NPSP) at the inlet to the Space Shuttle Main Engine (SSME) could have adverse effects on engine operation. A number of failures within both the External Tank (ET) and the Orbiter Main Propulsion System (MPS) could result in a low LH2 NPSP condition, which at extremely low levels can result in cavitation of SSME turbomachinery. Operational workarounds were developed to take advantage of the onboard crew s ability to manually throttle down the SSMEs (via the Pilot s Speedbrake/Throttle Controller), which alleviated the low LH2 NPSP condition. Manually throttling the SSME to a lower power level resulted in an increase in NPSP, mainly due to the reduction in frictional flow losses while at the lower throttle setting. Early in the Space Shuttle Program s history, the relevant Flight Rule for the Booster flight controller in Mission Control did not distinguish between ET and Orbiter MPS failures and the same crew action was taken for both. However, after a review of all Booster operational techniques following the Challenger disaster in the late 1980s, it was determined manually throttling the SSME to a lower power was only effective for Orbiter MPS failures and the Flight Rule was updated to reflect this change. The Flight Rule and associated crew actions initially called for a single throttle step to minimum power level when a low threshold for NPSP was met. As engineers refined their understanding of the NPSP requirements for the SSME (through a robust testing program), the operational techniques evolved to take advantage of the additional capabilities. This paper will examine the evolution of the Flight rule and associated procedure and how increases in knowledge about the SSME and the Space Shuttle vehicle as a whole have helped shape their development. What once was a single throttle step when NPSP decreased to a

  8. Excited state lifetime during photostimulated desorption of no from a Pt surface

    NASA Astrophysics Data System (ADS)

    Magkoev, T. T.

    1998-07-01

    We analyze the rotational energy distribution N(J) for NO molecules desorbed from a Pt (111) surface, taking into account the valence electron excitations, using a simple impulse model. We find a linear dependence between ln N(J) and (Er)1/2, where Er is the rotational energy of the desorbed molecules. The excited state lifetime and the critical residence time in the excited state, evaluated from the given dependences, are close to each other, and in order of magnitude are 10-15 s. We also estimate the frequency and amplitude of the tilting vibrations of the adsorbed molecules in the excited state.

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

    NASA Technical Reports Server (NTRS)

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

    1994-01-01

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

  10. Instability of insulating states in optical lattices due to collective phonon excitations

    NASA Astrophysics Data System (ADS)

    Yukalov, V. I.; Ziegler, K.

    2015-02-01

    The effect of collective phonon excitations on the properties of cold atoms in optical lattices is investigated. These phonon excitations are collective excitations, whose appearance is caused by intersite atomic interactions correlating the atoms, and they do not arise without such interactions. These collective excitations should not be confused with lattice vibrations produced by an external force. No such force is assumed. But the considered phonons are purely self-organized collective excitations, characterizing atomic oscillations around lattice sites, due to intersite atomic interactions. It is shown that these excitations can essentially influence the possibility of atoms' being localized. The states that would be insulating in the absence of phonon excitations can become delocalized when these excitations are taken into account. This concerns long-range as well as local atomic interactions. To characterize the region of stability, the Lindemann criterion is used.

  11. Dissociative excitation of the N(+)(5S) state by electron impact on N2 - Excitation function and quenching

    NASA Technical Reports Server (NTRS)

    Erdman, P. W.; Zipf, E. C.

    1986-01-01

    Metastable N(+)(5S) ions were produced in the laboratory by dissociative excitation of N2 with energetic electrons. The resulting radiative decay of the N(+)(5S) state was observed with sufficient resolution to completely resolve the doublet from the nearby N2 molecular radiation. The excitation function was measured from threshold to 500 eV. The cross section peaks at a high electron energy and also exhibits a high threshold energy both of which are typical of dissociative excitation-ionization processes. This finding complicates the explanation of electron impact on N2 as the mechanism for the source of the 2145 A 'auroral mystery feature' by further increasing the required peak cross section. It is suggested that the apparent N(+)(5S) quenching in auroras may be an artifact due to the softening of the electron energy spectrum in the auroral E region.

  12. Semiempirical Quantum-Chemical Orthogonalization-Corrected Methods: Benchmarks of Electronically Excited States.

    PubMed

    Tuna, Deniz; Lu, You; Koslowski, Axel; Thiel, Walter

    2016-09-13

    The semiempirical orthogonalization-corrected OMx methods have recently been shown to perform well in extensive ground-state benchmarks. They can also be applied to the computation of electronically excited states when combined with a suitable multireference configuration interaction (MRCI) treatment. We report on a comprehensive evaluation of the performance of the OMx/MRCI methods for electronically excited states. The present benchmarks cover vertical excitation energies, excited-state equilibrium geometries (including an analysis of significant changes between ground- and excited-state geometries), minimum-energy conical intersections, ground- and excited-state zero-point vibrational energies, and 0-0 transition energies for a total of 520 molecular structures and 412 excited states. For comparison, we evaluate the TDDFT/B3LYP method for all benchmark sets, and the CC2, MRCISD, and CASPT2 methods for some of them. We find that the current OMx/MRCI methods perform reasonably well for many of the excited-state properties. However, in comparison to the first-principles methods, there are also a number of shortcomings that should be addressed in future developments. PMID:27380455

  13. THE PHOTOTOXOICITY OF POLYCYCLIC AROMATIC HYDROCARBONS: A THEORETICAL STUDY OF EXCITED STATES AND CORRELATION TO EXPERIMENT

    EPA Science Inventory



    Investigators using models to determine the phototoxic effects of sunlight on polycyclic aromatic hydrocarbons (PAHS) have invoked the excited states of the molecule as important in elucidating the mechanism of these reactions. Energies of actual excited states were calcu...

  14. Semiempirical Quantum-Chemical Orthogonalization-Corrected Methods: Benchmarks of Electronically Excited States.

    PubMed

    Tuna, Deniz; Lu, You; Koslowski, Axel; Thiel, Walter

    2016-09-13

    The semiempirical orthogonalization-corrected OMx methods have recently been shown to perform well in extensive ground-state benchmarks. They can also be applied to the computation of electronically excited states when combined with a suitable multireference configuration interaction (MRCI) treatment. We report on a comprehensive evaluation of the performance of the OMx/MRCI methods for electronically excited states. The present benchmarks cover vertical excitation energies, excited-state equilibrium geometries (including an analysis of significant changes between ground- and excited-state geometries), minimum-energy conical intersections, ground- and excited-state zero-point vibrational energies, and 0-0 transition energies for a total of 520 molecular structures and 412 excited states. For comparison, we evaluate the TDDFT/B3LYP method for all benchmark sets, and the CC2, MRCISD, and CASPT2 methods for some of them. We find that the current OMx/MRCI methods perform reasonably well for many of the excited-state properties. However, in comparison to the first-principles methods, there are also a number of shortcomings that should be addressed in future developments.

  15. Excited State Absorption from Real-Time Time-Dependent Density Functional Theory.

    PubMed

    Fischer, Sean A; Cramer, Christopher J; Govind, Niranjan

    2015-09-01

    The optical response of excited states is a key property used to probe photophysical and photochemical dynamics. Additionally, materials with a large nonlinear absorption cross-section caused by two-photon (TPA) and excited state absorption (ESA) are desirable for optical limiting applications. The ability to predict the optical response of excited states would help in the interpretation of transient absorption experiments and aid in the search for and design of optical limiting materials. We have developed an approach to obtain excited state absorption spectra by combining real-time (RT) and linear-response (LR) time-dependent density functional theory (TDDFT). Being based on RT-TDDFT, our method is aimed at tackling larger molecular complexes and materials systems where excited state absorption is predominantly seen and many time-resolved experimental efforts are focused. To demonstrate our method, we have calculated the ground and excited state spectra of H₂⁺ and H₂ due to the simplicity in the interpretation of the spectra. We have validated our new approach by comparing our results for butadiene with previously published results based on quadratic response (QR). We also present results for oligofluorenes, where we compare our results with both QR-TDDFT and experimental measurements. Because our method directly measures the response of an excited state, stimulated emission features are also captured; although, these features are underestimated in energy which could be attributed to a change of the reference from the ground to the excited state.

  16. The origin of the split B800 absorption peak in the LH2 complexes from Allochromatium vinosum.

    PubMed

    Löhner, Alexander; Carey, Anne-Marie; Hacking, Kirsty; Picken, Nichola; Kelly, Sharon; Cogdell, Richard; Köhler, Jürgen

    2015-01-01

    The absorption spectrum of the high-light peripheral light-harvesting (LH) complex from the photosynthetic purple bacterium Allochromatium vinosum features two strong absorptions around 800 and 850 nm. For the LH2 complexes from the species Rhodopseudomonas acidophila and Rhodospirillum molischianum, where high-resolution X-ray structures are available, similar bands have been observed and were assigned to two pigment pools of BChl a molecules that are arranged in two concentric rings (B800 and B850) with nine (acidophila) or eight (molischianum) repeat units, respectively. However, for the high-light peripheral LH complex from Alc. vinosum, the intruiging feature is that the B800 band is split into two components. We have studied this pigment-protein complex by ensemble CD spectroscopy and polarisation-resolved single-molecule spectroscopy. Assuming that the high-light peripheral LH complex in Alc. vinosum is constructed on the same modular principle as described for LH2 from Rps. acidophila and Rsp. molischianum, we used those repeat units as a starting point for simulating the spectra. We find the best agreement between simulation and experiment for a ring-like oligomer of 12 repeat units, where the mutual arrangement of the B800 and B850 rings resembles those from Rsp. molischianum. The splitting of the B800 band can be reproduced if both an excitonic coupling between dimers of B800 molecules and their interaction with the B850 manifold are taken into account. Such dimers predict an interesting apoprotein organisation as discussed below. PMID:25150556

  17. Preliminary base heating environments for a generalized ALS LO2/LH2 launch vehicle, appendix 1 and 2

    NASA Technical Reports Server (NTRS)

    Bender, Robert L.; Reardon, John E.

    1989-01-01

    A secondary objective of contract NAS8-39141 is to provide base heating assessments, as required, to support Advanced Launch System (ALS) preliminary launch vehicle and propulsion system design studies. The ALS propulsion systems integration working group meeting (No. 3) recently completed in San Diego, California, focused attention on the need for base heating environment determination to provide preliminary requirements for LO2/LH2 propulsion systems currently being considered for ALS. We were requested to provide these environments for a range of possible propellant mixture and nozzle area ratios. Base heating environments can only be determined as a function of altitude when the engine operating conditions and vehicle base region geometry (engine arrangement) are known. If time dependent environments are needed to assess thermal loads, a trajectory must also be provided. These parameters are not fixed at this time since the ALS configurations and propulsion operating conditions are varied and continue to be studied by Phase B contractors. Therefore, for this study, a generalized LO2/LH2 system was selected along with a vehicle configuration consisting of a seven-engine booster and a three-engine core. MSFC provided guidance for the selection. We also selected a limited number of body points on the booster and core vehicles and engines for the environment estimates. Environments at these locations are representative of maximum heating conditions in the base region and are provided as a function of altitude only. Guidelines and assumptions for this assessment, methodology for determining the environments, and preliminary results are provided in this technical note. Refinements in the environments will be provided as the ALS design matures.

  18. The origin of the split B800 absorption peak in the LH2 complexes from Allochromatium vinosum.

    PubMed

    Löhner, Alexander; Carey, Anne-Marie; Hacking, Kirsty; Picken, Nichola; Kelly, Sharon; Cogdell, Richard; Köhler, Jürgen

    2015-01-01

    The absorption spectrum of the high-light peripheral light-harvesting (LH) complex from the photosynthetic purple bacterium Allochromatium vinosum features two strong absorptions around 800 and 850 nm. For the LH2 complexes from the species Rhodopseudomonas acidophila and Rhodospirillum molischianum, where high-resolution X-ray structures are available, similar bands have been observed and were assigned to two pigment pools of BChl a molecules that are arranged in two concentric rings (B800 and B850) with nine (acidophila) or eight (molischianum) repeat units, respectively. However, for the high-light peripheral LH complex from Alc. vinosum, the intruiging feature is that the B800 band is split into two components. We have studied this pigment-protein complex by ensemble CD spectroscopy and polarisation-resolved single-molecule spectroscopy. Assuming that the high-light peripheral LH complex in Alc. vinosum is constructed on the same modular principle as described for LH2 from Rps. acidophila and Rsp. molischianum, we used those repeat units as a starting point for simulating the spectra. We find the best agreement between simulation and experiment for a ring-like oligomer of 12 repeat units, where the mutual arrangement of the B800 and B850 rings resembles those from Rsp. molischianum. The splitting of the B800 band can be reproduced if both an excitonic coupling between dimers of B800 molecules and their interaction with the B850 manifold are taken into account. Such dimers predict an interesting apoprotein organisation as discussed below.

  19. A Doubles Correction to Electronic Excited States from Configuration Interaction in the Space of Single Substitutions

    NASA Technical Reports Server (NTRS)

    Head-Gordon, Martin; Rico, Rudolph J.; Lee, Timothy J.; Oumi, Manabu

    1994-01-01

    A perturbative correction to the method of configuration interaction with single substitutions (CIS) is presented. This CIS(D) correction approximately introduces the effect of double substitutions which are absent in CIS excited states. CIS(D) is a second-order perturbation expansion of the coupled-cluster excited state method, restricted to single and double substitutions, in a series in which CIS is zeroth order, and the first-order correction vanishes. CIS (D) excitation energies are size consistent and the calculational complexity scales with the fifth power of molecular size, akin to second-order Moller-Plesset theory for the ground state. Calculations on singlet excited states of ethylene, formaldehyde, acetaldehyde, butadiene and benzene show that CIS (D) is a uniform improvement over CIS. CIS(D) appears to be a promising method for examining excited states of large molecules, where more accurate methods are not feasible.

  20. Theoretical Study of Tautomerization Reactions for the Ground and First Excited Electronic States of Adenine

    NASA Technical Reports Server (NTRS)

    Salter, Latasha M.; Chaban, Galina M.; Kwak, Dochan (Technical Monitor)

    2002-01-01

    Geometrical structures and energetic properties for different tautomers of adenine are calculated in this study, using multi-configurational wave functions. Both the ground and the lowest singlet excited state potential energy surfaces are studied. Four tautomeric forms are considered, and their energetic order is found to be different on the ground and the excited state potential energy surfaces. Minimum energy reaction paths are obtained for hydrogen atom transfer (tautomerization) reactions in the ground and the lowest excited electronic states. It is found that the barrier heights and the shapes of the reaction paths are different for the ground and the excited electronic states, suggesting that the probability of such tautomerization reaction is higher on the excited state potential energy surface. This tautomerization process should become possible in the presence of water or other polar solvent molecules and should play an important role in the photochemistry of adenine.

  1. Extension of Light-Harvesting Ability of Photosynthetic Light-Harvesting Complex 2 (LH2) through Ultrafast Energy Transfer from Covalently Attached Artificial Chromophores.

    PubMed

    Yoneda, Yusuke; Noji, Tomoyasu; Katayama, Tetsuro; Mizutani, Naoto; Komori, Daisuke; Nango, Mamoru; Miyasaka, Hiroshi; Itoh, Shigeru; Nagasawa, Yutaka; Dewa, Takehisa

    2015-10-14

    Introducing appropriate artificial components into natural biological systems could enrich the original functionality. To expand the available wavelength range of photosynthetic bacterial light-harvesting complex 2 (LH2 from Rhodopseudomonas acidophila 10050), artificial fluorescent dye (Alexa Fluor 647: A647) was covalently attached to N- and C-terminal Lys residues in LH2 α-polypeptides with a molar ratio of A647/LH2 ≃ 9/1. Fluorescence and transient absorption spectroscopies revealed that intracomplex energy transfer from A647 to intrinsic chromophores of LH2 (B850) occurs in a multiexponential manner, with time constants varying from 440 fs to 23 ps through direct and B800-mediated indirect pathways. Kinetic analyses suggested that B800 chromophores mediate faster energy transfer, and the mechanism was interpretable in terms of Förster theory. This study demonstrates that a simple attachment of external chromophores with a flexible linkage can enhance the light harvesting activity of LH2 without affecting inherent functions of energy transfer, and can achieve energy transfer in the subpicosecond range. Addition of external chromophores, thus, represents a useful methodology for construction of advanced hybrid light-harvesting systems that afford solar energy in the broad spectrum.

  2. Vibrations of acrylonitrile in N 1s excited states

    NASA Astrophysics Data System (ADS)

    Ilakovac, V.; Carniato, S.; Gallet, J.-J.; Kukk, E.; Horvatić, D.; Ilakovac, A.

    2008-01-01

    The N 1s near edge x-ray absorption fine structure spectra of acrylonitrile gas are accurately reproduced by a complete ab initio multidimensional vibrational analysis. The role of π∗ -orbital localization and hybridization on vibrations accompanying core excitation is discussed. Transition to the π⊥∗(C=C-C≡N) delocalized orbital excites mostly stretching vibrations of the whole spinal column of the molecule. Promoting a core electron to the localized π∥∗(C≡N) produces C≡N stretching vibration combined with two strong bending modes of the C-C≡N end of the molecule, related to the change of carbon hybridization.

  3. Variational state specific solvent models for excited states from time dependent self-consistent field methods

    NASA Astrophysics Data System (ADS)

    Bjorgaard, Josiah; Velizhanin, Kirill; Tretiak, Sergei

    2015-03-01

    The effect of a dielectric environment on a molecule can be profound, causing changes in nuclear configuration and electronic structure. Quantum chemical simulation of a solute-solvent system can be prohibitively expensive due to the large number of degrees of freedom attributed to the solvent. To remedy this, the solvent can be treated as a dielectric cavity. Mutual polarization of the solute and solvent must be considered for accurate treatment of an optically excited state (ES) with a state-specific solvent model (SSM). In vacuum, time dependent self-consistent field (TD-SCF) methods (e,g, TD-HF, TD-DFT) give variational excitation energies. With the well known Z-vector equation, a variational ES energy is used to explore the ES potential energy surface (PES) with analytical gradients. Modification of the standard TD-SCF eigensystem to accommodate a SSM creates a nonlinear TD-SCF equation with non-variational excitation energies. This prevents analytical gradients from being formulated so that the ES PES cannot be explored. Here, we show how a variational formulation of existing SSMs can be derived from a Lagrangian formalism and give numerical results for the variability of calculated quantities. Model dynamics using SSMs are showcased.

  4. Electronically Excited States in Poly(p-phenylenevinylene): Vertical Excitations and Torsional Potentials from High-Level Ab Initio Calculations

    PubMed Central

    2013-01-01

    Ab initio second-order algebraic diagrammatic construction (ADC(2)) calculations using the resolution of the identity (RI) method have been performed on poly-(p-phenylenevinylene) (PPV) oligomers with chain lengths up to eight phenyl rings. Vertical excitation energies for the four lowest π–π* excitations and geometry relaxation effects for the lowest excited state (S1) are reported. Extrapolation to infinite chain length shows good agreement with analogous data derived from experiment. Analysis of the bond length alternation (BLA) based on the optimized S1 geometry provides conclusive evidence for the localization of the defect in the center of the oligomer chain. Torsional potentials have been computed for the four excited states investigated and the transition densities divided into fragment contributions have been used to identify excitonic interactions. The present investigation provides benchmark results, which can be used (i) as reference for lower level methods and (ii) give the possibility to parametrize an effective Frenkel exciton Hamiltonian for quantum dynamical simulations of ultrafast exciton transfer dynamics in PPV type systems. PMID:23427902

  5. Direct Visualization of Excited-State Symmetry Breaking Using Ultrafast Time-Resolved Infrared Spectroscopy.

    PubMed

    Dereka, Bogdan; Rosspeintner, Arnulf; Li, Zhiquan; Liska, Robert; Vauthey, Eric

    2016-04-01

    Most symmetric quadrupolar molecules designed for two-photon absorption behave as dipolar molecules in the S1 electronic excited state. This is usually explained by a breakup of the symmetry in the excited state. However, the origin of this process and its dynamics are still not fully understood. Here, excited-state symmetry breaking in a quadrupolar molecule with a D-π-A-π-D motif, where D and A are electron donating and accepting units, is observed in real time using ultrafast transient infrared absorption spectroscopy. The nature of the relaxed S1 state was found to strongly depend on the solvent polarity: (1) in nonpolar solvents, it is symmetric and quadrupolar; (2) in weakly polar media, the quadrupolar state observed directly after excitation transforms to a symmetry broken S1 state with one arm bearing more excitation than the other; and (3) in highly polar solvents, the excited state evolves further to a purely dipolar S1 state with the excitation localized entirely on one arm. The time scales associated with the transitions between these states coincide with those of solvation dynamics, indicating that symmetry breaking is governed by solvent fluctuations.

  6. Exotic and excited-state meson spectroscopy and radiative transitions from lattice QCD

    SciTech Connect

    Christopher Thomas

    2010-09-01

    We discuss recent progress in extracting the excited meson spectrum and radiative transition form factors using lattice QCD. We mention results in the charmonium sector, including the first lattice QCD calculation of radiative transition rates involving excited charmonium states, highlighting results for high spin and exotic states. We present recent results on a highly excited isovector meson spectrum from dynamical anisotropic lattices. Using carefully constructed operators we show how the continuum spin of extracted states can be reliably identified and confidently extract excited states, states with exotic quantum numbers and states of high spin. This spectrum includes the first spin-four state extracted from lattice QCD. We conclude with some comments on future prospects.

  7. The phototoxicity of polycyclic aromatic hydrocarbons: a theoretical study of excited states and correlation to experiment.

    PubMed

    Betowski, Leon D; Enlow, Mark; Riddick, Lee

    2002-06-01

    Investigators using models to determine the phototoxic effects of sunlight on polycyclic aromatic hydrocarbons (PAHs) have invoked the excited states of the molecule as important in elucidating the mechanism of these reactions. Energies of actual excited states were calculated for ten PAHs by several ab initio methods. The main method used for these calculations was the Configuration Interaction approach, modeling excited states as combinations of single substitutions out of the Hartree-Fock ground state. These calculations correlate well with both experimentally measured singlet and triplet state energies and also previous HOMO-LUMO gap energies that approximate the singlet state energies. The excited state calculations then correlate well with general models of photo-induced toxicity based for the PAHs.

  8. Lifetime measurement of excited states in /sup 105/Ag

    SciTech Connect

    Mittal, V.K.; Govil, I.M.

    1986-11-01

    The levels up to about 2.1 MeV in /sup 105/Ag were excited via /sup 105/Pd(p,n..gamma..) reaction. For the first time, lifetimes of energy levels at 1023, 1042, 1097, 1166, 1243, 1295, 1328, 1386, 1442, 1543, 1558, 1587, 1719, 1923, and 2081 keV have been measured using the Doppler shift attenuation technique.

  9. Eliminating LH2 in LOX-collect space launchers - Key to on-demand capability

    NASA Astrophysics Data System (ADS)

    Leingang, J. L.; Carreiro, L. R.; Maurice, L. Q.

    1993-06-01

    Two air-breathing reusable two-stage space launch vehicle concepts are proposed, in which the first stage employs turboramjet propulsion and the second stage uses rockets, which are expected to provide very rapid response launch of 10,000 lb polar-orbit payloads. In both concepts, liquid oxygen (LOX) for the second stage is collected during first stage ascent, thus eliminating the need for LOX ground servicing facilities. In the first concept, liquid hydrogen in the amount just sufficient to condense and collect second state LOX is the only cryogenic fluid that is loaded on the vehicle at takeoff. The second concept uses the heat sink of conventional jet propulsion fuel and water coolant to drive a lightweight adaptation of the commercial LOX production process, eliminating all cryogenics at takeoff. Both concepts should permit true launch-on-demand capability with aircraftlike ground operations.

  10. Eliminating LH2 in LOX-collect space launchers - Key to on-demand capability

    NASA Technical Reports Server (NTRS)

    Leingang, J. L.; Carreiro, L. R.; Maurice, L. Q.

    1993-01-01

    Two air-breathing reusable two-stage space launch vehicle concepts are proposed, in which the first stage employs turboramjet propulsion and the second stage uses rockets, which are expected to provide very rapid response launch of 10,000 lb polar-orbit payloads. In both concepts, liquid oxygen (LOX) for the second stage is collected during first stage ascent, thus eliminating the need for LOX ground servicing facilities. In the first concept, liquid hydrogen in the amount just sufficient to condense and collect second state LOX is the only cryogenic fluid that is loaded on the vehicle at takeoff. The second concept uses the heat sink of conventional jet propulsion fuel and water coolant to drive a lightweight adaptation of the commercial LOX production process, eliminating all cryogenics at takeoff. Both concepts should permit true launch-on-demand capability with aircraftlike ground operations.

  11. Self-Consistent Optimization of Excited States within Density-Functional Tight-Binding.

    PubMed

    Kowalczyk, Tim; Le, Khoa; Irle, Stephan

    2016-01-12

    We present an implementation of energies and gradients for the ΔDFTB method, an analogue of Δ-self-consistent-field density functional theory (ΔSCF) within density-functional tight-binding, for the lowest singlet excited state of closed-shell molecules. Benchmarks of ΔDFTB excitation energies, optimized geometries, Stokes shifts, and vibrational frequencies reveal that ΔDFTB provides a qualitatively correct description of changes in molecular geometries and vibrational frequencies due to excited-state relaxation. The accuracy of ΔDFTB Stokes shifts is comparable to that of ΔSCF-DFT, and ΔDFTB performs similarly to ΔSCF with the PBE functional for vertical excitation energies of larger chromophores where the need for efficient excited-state methods is most urgent. We provide some justification for the use of an excited-state reference density in the DFTB expansion of the electronic energy and demonstrate that ΔDFTB preserves many of the properties of its parent ΔSCF approach. This implementation fills an important gap in the extended framework of DFTB, where access to excited states has been limited to the time-dependent linear-response approach, and affords access to rapid exploration of a valuable class of excited-state potential energy surfaces.

  12. Excited-state wavepacket and potential reconstruction by coherent anti-Stokes Raman scattering.

    PubMed

    Avisar, David; Tannor, David J

    2015-01-28

    Among the major challenges in the chemical sciences is controlling chemical reactions and deciphering their mechanisms. Since much of chemistry occurs in excited electronic states, in the last three decades scientists have employed a wide variety of experimental techniques and theoretical methods to recover excited-state potential energy surfaces and the wavepackets that evolve on them. These methods have been partially successful but generally do not provide a complete reconstruction of either the excited state wavepacket or potential. We have recently proposed a methodology for reconstructing excited-state molecular wavepackets and the corresponding potential energy surface [Avisar and Tannor, Phys. Rev. Lett., 2011, 106, 170405]. In our approach, the wavepacket is represented as a superposition of the set of vibrational eigenfunctions of the molecular ground-state Hamiltonian. We assume that the multidimensional ground-state potential surface is known, and therefore these vibrational eigenfunctions are known as well. The time-dependent coefficients of the basis functions are obtained by experimental measurement of the resonant coherent anti-Stokes Raman scattering (CARS) signal. Our reconstruction strategy has several significant advantages: (1) the methodology requires no a priori knowledge of any excited-state potential. (2) It applies to dissociative as well as to bound excited-state potentials. (3) It is general for polyatomics. (4) The excited-state potential surface is reconstructed simultaneously with the wavepacket. Apart from making a general contribution to the field of excited-state spectroscopy, our method provides the information on the excited-state wavepacket and potential necessary to design laser pulse sequences to control photochemical reactions.

  13. Protolytic dissociation of cyano derivatives of naphthol, biphenyl and phenol in the excited state: A review

    NASA Astrophysics Data System (ADS)

    Szczepanik, Beata

    2015-11-01

    The excited state proton transfer (ESPT) has been extensively studied for hydroxyarenes, phenols, naphthols, hydroxystilbenes, etc., which undergo large enhancement of acidity upon electronic excitation, thus classified as photoacids. The changes of acidic character in the excited state of cyano-substituted derivatives of phenol, hydroxybiphenyl and naphthol are reviewed in this paper. The acidity constants pKa in the ground state (S0), pKa∗ in the first singlet excited state (S1) and the change of the acidity constant in the excited state ΔpKa for the discussed compounds are summarized and compared. The results of the acidity studies show, that the "electro-withdrawing" CN group in the molecules of naphthol, hydroxybiphenyl and phenol causes dramatic increase of their acidity in the excited state in comparison to the ground state. This effect is greatest for the cyanonaphthols (the doubly substituted CN derivatives are almost as strong as a mineral acid in the excited state), comparable for cyanobiphenyls, and smaller for phenol derivatives. The increase of acidity enables proton transfer to various organic solvents, and the investigation of ESPT can be extended to a variety of solvents besides water. The results of theoretical investigations were also presented and used for understanding the protolytic equilibria of cyano derivatives of naphthol, hydroxybiphenyl and phenol.

  14. Excited state X-ray absorption spectroscopy: Probing both electronic and structural dynamics

    NASA Astrophysics Data System (ADS)

    Neville, Simon P.; Averbukh, Vitali; Ruberti, Marco; Yun, Renjie; Patchkovskii, Serguei; Chergui, Majed; Stolow, Albert; Schuurman, Michael S.

    2016-10-01

    We investigate the sensitivity of X-ray absorption spectra, simulated using a general method, to properties of molecular excited states. Recently, Averbukh and co-workers [M. Ruberti et al., J. Chem. Phys. 140, 184107 (2014)] introduced an efficient and accurate L 2 method for the calculation of excited state valence photoionization cross-sections based on the application of Stieltjes imaging to the Lanczos pseudo-spectrum of the algebraic diagrammatic construction (ADC) representation of the electronic Hamiltonian. In this paper, we report an extension of this method to the calculation of excited state core photoionization cross-sections. We demonstrate that, at the ADC(2)x level of theory, ground state X-ray absorption spectra may be accurately reproduced, validating the method. Significantly, the calculated X-ray absorption spectra of the excited states are found to be sensitive to both geometric distortions (structural dynamics) and the electronic character (electronic dynamics) of the initial state, suggesting that core excitation spectroscopies will be useful probes of excited state non-adiabatic dynamics. We anticipate that the method presented here can be combined with ab initio molecular dynamics calculations to simulate the time-resolved X-ray spectroscopy of excited state molecular wavepacket dynamics.

  15. UV-induced DNA Damage: The Role of Electronic Excited States.

    PubMed

    Markovitsi, Dimitra

    2016-01-01

    The knowledge of the fundamental processes induced by the direct absorption of UV radiation by DNA allows extrapolating conclusions drawn from in vitro studies to the in-vivo DNA photoreactivity. In this respect, the characterization of the DNA electronic excited states plays a key role. For a long time, the mechanisms of DNA lesion formation were discussed in terms of generic "singlet" and "triplet" excited state reactivity. However, since the beginning of the 21(st) century, both experimental and theoretical studies revealed the existence of "collective" excited states, i.e. excited states delocalized over at least two bases. Two limiting cases are distinguished: Frenkel excitons (delocalized ππ* states) and charge-transfer states in which positive and negative charges are located on different bases. The importance of collective excited states in photon absorption (in particular in the UVA spectral domain), the redistribution of the excitation energy within DNA, and the formation of dimeric pyrimidine photoproducts is discussed. The dependence of the behavior of the collective excited states on conformational motions of the nucleic acids is highlighted.

  16. Two-electron excitation in slow ion-atom collisions: Excitation mechanisms and interferences among autoionizing states

    SciTech Connect

    Kimura, M. Rice Univ., Houston, TX . Dept. of Physics)

    1990-01-01

    The two-electron capture or excitation process resulting from collisions of H{sup +} and O{sup 6+} ions with He atoms in the energy range from 0.5 keV/amu to 5 keV/amu is studied within a molecular representation. The collision dynamics for formation of doubly excited O{sup 4+} ions and He** atoms and their (n{ell}, n{prime}{ell}{prime}) populations are analyzed in conjunction with electron correlations. Autoionizing states thus formed decay through the Auger process. An experimental study of an ejected electron energy spectrum shows ample structures in addition to two characteristic peaks that are identified by atomic and molecular autoionizations. These structures are attributable to various interferences among electronic states and trajectories. We examine the dominant sources of the interferences. 12 refs., 5 figs.

  17. Estimation of first excited singlet-state dipole moments of aminoanthraquinones by solvatochromic method.

    PubMed

    Siddlingeshwar, B; Hanagodimath, S M

    2009-04-01

    The ground state (micro(g)) and the excited state (micro(e)) dipole moments of three substituted anthraquinones, namely 1-aminoanthracene-9,10-dione (AAQ), 1-(methylamino)anthracence-9,10-dione (MAQ) and 1,5-diaminoanthracene-9,10-dione (DAQ) were estimated in various solvents. The dipole moments (micro(g) and micro(e)) were estimated from Lippert, Bakhshiev, Kawski-Chamma-Viallet, McRae and Suppan equations by using the variation of Stokes shift with the solvent dielectric constant and refractive index. The excited state dipole moments were also calculated by using the variation of Stokes shift with microscopic solvent polarity parameter (Epsilon(T)(N)). It was observed that dipole moment values of excited states (micro(e)) were higher than corresponding ground state values (micro(g)), indicating a substantial redistribution of the pi-electron densities in a more polar excited state for all the molecules investigated.

  18. Excited state absorption of pump radiation as a loss mechanism in solid-state lasers

    SciTech Connect

    Kliewer, M.L.; Powell, R.C.

    1989-08-01

    The characteristics of optical pumping dynamics occurring in laser-pumped rare earth-doped, solid-state laser materials were investigated by using a tunable alexandrite laser to pump Y/sub 3/Al/sub 5/O/sub 12/:Nd/sup 3+/ in an optical cavity. It was found that the slope efficiency of the Nd laser operation depends strongly on the wavelength of the pump laser. For pump wavelengths resulting in low slope efficiencies, intense fluorescence emission is observed from the sample in the blue-green spectral region. This is attributed to the excited state absorption of pump photons which occurs during radiationless relaxation from the pump band to the metastable state. This type of process will be an important loss mechanism for monochromatic pumping of laser systems at specific pump wavelengths.

  19. Excited-state absorption of pump radiation as a loss mechanism in solid-state lasers

    SciTech Connect

    Kliewer, M.L.; Powell, R.C.

    1989-08-01

    The characteristics of optical pumping dynamics occuring in laser-pumped rare earth-doped, solid-state laser materials were investigated by using a tunable alexandrite laser to pump Y3Al5O12:Nd(3+) in an optical cavity. It was found that the slope efficiency of the Nd laser operation depends strongly on the wavelength of the pump laser. For pump wavelength resulting in low slope efficiencies, intense fluorescence emission is observed form the sample in the blue-green spectral region. This is attributed to the excited state absorption of pump photons which occurs during radiationless relaxation from the pump band to the metastable state. This type of process will be an important loss mechanism for monochromatic pumping of laser systems at specific pump wavelengths.

  20. Excited state absorption of pump radiation as a loss mechanism in solid-state lasers

    NASA Technical Reports Server (NTRS)

    Kliewer, Michael L.; Powell, Richard C.

    1989-01-01

    The characteristics of optical pumping dynamics in laser-pumped, rare-earth-doped, solid-state laser materials are investigated by using a tunable alexandrite laser to pump Y3Al5O12:Nd(3+) in an optical cavity. It is found that the slope efficiency of the Nd laser operation depends strongly on the wavelength of the pump laser. For pump wavelengths resulting in low slope efficiencies, intense fluorescence emission is observed from the sample in the blue-green spectral region. This is attributed to the excited-state absorption of pump photons which occurs during radiationless relaxation from the pump band to the metastable state. This type of process is an important loss mechanism for monochromatic pumping of laser systems at specific pump wavelengths.

  1. Excited triplet states as photooxidants in surface waters

    NASA Astrophysics Data System (ADS)

    Canonica, S.

    2012-12-01

    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

  2. Excited State Electronic Properties of Sodium Iodide and Cesium Iodide

    SciTech Connect

    Campbell, Luke W.; Gao, Fei

    2013-05-01

    We compute from first principles the dielectric function, loss function, lifetime and scattering rate of quasiparticles due to electronic losses, and secondary particle spectrum due to plasmon decay in two scintillating alkali halides, sodium iodide and cesium iodide. Particular emphasis is placed on quasiparticles within several multiples of the band gap from the band edges. A theory for the decay spectra of plasmons and other electronic excitations in crystals is presented. Applications to Monte Carlo radiation transport codes are discussed.

  3. "Inverted" Solvent Effect on Charge Transfer in the Excited State.

    PubMed

    Nau; Pischel

    1999-10-01

    Faster in cyclohexane than in acetonitrile is the fluorescence quenching of the azoalkane 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO) by amines and sulfides. Although this photoreaction is induced by charge transfer (CT; see picture) and exciplexes are formed, the increase in the dipole moment of the exciplex is not large enough to offset the solvent stabilization of the excited reactants, and an "inverted" solvent effect results.

  4. Excited states in the active media of oxygen - iodine lasers

    SciTech Connect

    Azyazov, V N

    2009-11-30

    A review of investigations of kinetic processes in active media oxygen - iodine lasers (OILs) performed in the last decade is presented. The mechanisms of pumping and quenching of electronically and vibrationally excited O{sub 2} and I{sub 2} molecules are considered, and dissociation mechanisms of I{sub 2} in the active medium of the OIL are analysed. The values of kinetic constants of processes proceeding in the active media of OILs are recommended. (review)

  5. High-energy excited states in 98Cd

    NASA Astrophysics Data System (ADS)

    Blazhev, A.; Braun, N.; Grawe, H.; Boutachkov, P.; Nara Singh, B. S.; Brock, T.; Liu, Zh; Wadsworth, R.; Górska, M.; Jolie, J.; Nowacki, F.; Pietri, S.; Domingo-Pardo, C.; Kojouharov, I.; Caceres, L.; Engert, T.; Farinon, F.; Gerl, J.; Goel, N.; Grȩbosz, J.; Hoischen, R.; Kurz, N.; Nociforo, C.; Prochazka, A.; Schaffner, H.; Steer, S.; Weick, H.; Wollersheim, H.-J.; Ataç, A.; Bettermann, L.; Eppinger, K.; Faestermann, T.; Finke, F.; Geibel, K.; Hinke, C.; Gottardo, A.; Ilie, G.; Iwasaki, H.; Krücken, R.; Merchan, E.; Nyberg, J.; Pfützner, M.; Podolyák, Zs; Regan, P.; Reiter, P.; Rinta-Antila, S.; Rudolph, D.; Scholl, C.; Söderström, P.-A.; Warr, N.; Woods, P.

    2010-01-01

    In 98Cd a new high-energy isomeric γ-ray transition was identified, which confirms previous spin-parity assignments and enables for the first time the measurement of the E2 and E4 strength for the two decay branches of the isomer. Preliminary results on the 98Cd high-excitation level scheme are presented. A comparison to shell-model calculations as well as implications for the nuclear structure around 100Sn are discussed.

  6. Dark excited States of carotenoid regulated by bacteriochlorophyll in photosynthetic light harvesting.

    PubMed

    Nakamura, Ryosuke; Nakagawa, Katsunori; Nango, Mamoru; Hashimoto, Hideki; Yoshizawa, Masayuki

    2011-03-31

    In photosynthesis, carotenoids play important roles in light harvesting (LH) and photoprotective functions, which have been described mainly in terms of two singlet excited states of carotenoids: S(1) and S(2). In addition to the "dark" S(1) state, another dark state, S*, was recently identified and its involvement in photosynthetic functions was determined. However, there is no consistent picture concerning its nature or the mechanism of its formation. One particularly anomalous behavior obtained from femtosecond transient absorption (TA) spectroscopy is that the S*/S(1) population ratio depends on the excitation intensity. Here, we focus on the effect of nearby bacteriochlorophyll (BChl) on the relaxation dynamics of carotenoid in the LH complex. We performed femtosecond TA spectroscopy combined with pre-excitation of BChl in the reconstituted LH1 complex from Rhodospirillum rubrum S1. We observed that the energy flow from S(1), including its vibrationally excited hot states, to S* occurs only when nearby BChl is excited into Q(y), resulting in an increase in S*/S(1). We also examined the excitation-intensity dependence of S*/S(1) by conventional TA spectroscopy. A comparison between the pre-excitation effect and excitation-intensity dependence shows a strong correlation of S*/S(1) with the number of BChls excited into Q(y). In addition, we observed an increase in triplet formation as the S* population increased, indicating that S* is an electronic excited state that is the precursor to triplet formation. Our findings provide an explanation for observed spectroscopic features, including the excitation-intensity dependences debated so far, and offer new insights into energy deactivation mechanisms inherent in the LH antenna.

  7. Reconstruction of an excited-state molecular wave packet with attosecond transient absorption spectroscopy

    NASA Astrophysics Data System (ADS)

    Cheng, Yan; Chini, Michael; Wang, Xiaowei; González-Castrillo, Alberto; Palacios, Alicia; Argenti, Luca; Martín, Fernando; Chang, Zenghu

    2016-08-01

    Attosecond science promises to allow new forms of quantum control in which a broadband isolated attosecond pulse excites a molecular wave packet consisting of a coherent superposition of multiple excited electronic states. This electronic excitation triggers nuclear motion on the molecular manifold of potential energy surfaces and can result in permanent rearrangement of the constituent atoms. Here, we demonstrate attosecond transient absorption spectroscopy (ATAS) as a viable probe of the electronic and nuclear dynamics initiated in excited states of a neutral molecule by a broadband vacuum ultraviolet pulse. Owing to the high spectral and temporal resolution of ATAS, we are able to reconstruct the time evolution of a vibrational wave packet within the excited B'Σ1u+ electronic state of H2 via the laser-perturbed transient absorption spectrum.

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

    NASA Astrophysics Data System (ADS)

    Joshi, Sunita; Pant, Debi D.

    2012-06-01

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

  9. Entropy, chaos, and excited-state quantum phase transitions in the Dicke model.

    PubMed

    Lóbez, C M; Relaño, A

    2016-07-01

    We study nonequilibrium processes in an isolated quantum system-the Dicke model-focusing on the role played by the transition from integrability to chaos and the presence of excited-state quantum phase transitions. We show that both diagonal and entanglement entropies are abruptly increased by the onset of chaos. Also, this increase ends in both cases just after the system crosses the critical energy of the excited-state quantum phase transition. The link between entropy production, the development of chaos, and the excited-state quantum phase transition is more clear for the entanglement entropy. PMID:27575109

  10. Nonequilibrium solvent effects in Born-Oppenheimer molecular dynamics for ground and excited electronic states

    NASA Astrophysics Data System (ADS)

    Bjorgaard, J. A.; Velizhanin, K. A.; Tretiak, S.

    2016-04-01

    The effects of solvent on molecular processes such as excited state relaxation and photochemical reaction often occurs in a nonequilibrium regime. Dynamic processes such as these can be simulated using excited state molecular dynamics. In this work, we describe methods of simulating nonequilibrium solvent effects in excited state molecular dynamics using linear-response time-dependent density functional theory and apparent surface charge methods. These developments include a propagation method for solvent degrees of freedom and analytical energy gradients for the calculation of forces. Molecular dynamics of acetaldehyde in water or acetonitrile are demonstrated where the solute-solvent system is out of equilibrium due to photoexcitation and emission.

  11. {alpha} decays to ground and excited states of heavy deformed nuclei

    SciTech Connect

    Denisov, V. Yu.; Khudenko, A. A.

    2009-09-15

    The experimental data for {alpha}-decay half-lives to ground and excited states of deformed nuclei with 222{<=}A{<=}252 and 88{<=}Z{<=}102 are analyzed in the framework of the unified model for {alpha} decay and {alpha} capture. The branching ratios to excited states depend on the energy and the angular momentum of the {alpha} particle. The evaluated branching ratios for 0{sub g.s.}{sup +}{yields}0{sub g.s.}{sup +},2{sup +},4{sup +} {alpha} transitions in even-even nuclei agree with the experimental data. The experimental and calculated branching ratios for {alpha} transitions into more highly excited states are similar.

  12. Entropy, chaos, and excited-state quantum phase transitions in the Dicke model

    NASA Astrophysics Data System (ADS)

    Lóbez, C. M.; Relaño, A.

    2016-07-01

    We study nonequilibrium processes in an isolated quantum system—the Dicke model—focusing on the role played by the transition from integrability to chaos and the presence of excited-state quantum phase transitions. We show that both diagonal and entanglement entropies are abruptly increased by the onset of chaos. Also, this increase ends in both cases just after the system crosses the critical energy of the excited-state quantum phase transition. The link between entropy production, the development of chaos, and the excited-state quantum phase transition is more clear for the entanglement entropy.

  13. Properties of the first excited state of nonbipartite Heisenberg spin rings

    NASA Astrophysics Data System (ADS)

    Schnack, J.

    2000-12-01

    Systematic properties of the first excited state are presented for various ring sizes and spin quantum numbers which are only partly covered by the theorem of Lieb, Schultz, and Mattis. For odd ring sizes the first excited energy eigenvalue shows unexpected degeneracy and related shift quantum numbers. As a byproduct the ground state energy as well as the energy of the first excited state of infinite chains are calculated by extrapolating the properties of only a few, finite, antiferromagnetically coupled Heisenberg rings using the powerful Levin sequence acceleration method.

  14. Aurora Borealis: stochastic cellular automata simulations of the excited-state dynamics of oxygen atoms.

    NASA Astrophysics Data System (ADS)

    Seybold, P. G.; Kier, L. B.; Cheng, C.-K.

    1999-12-01

    Emissions from the 1S and 1D excited states of atomic oxygen play a prominent role in creating the dramatic light displays (aurora borealis) seen in the skies over polar regions of the Northern Hemisphere. A probabilistic asynchronous cellular automaton model described previously has been applied to the excited-state dynamics of atomic oxygen. The model simulates the time-dependent variations in ground (3P) and excited-state populations that occur under user-defined probabilistic transition rules for both pulse and steady-state conditions. Although each trial simulation is itself an independent "experiment", deterministic values for the excited-state emission lifetimes and quantum yields emerge as limiting cases for large numbers of cells or large numbers of trials. Stochastic variations in the lifetimes and emission yields can be estimated from repeated trials.

  15. Ultrafast Excited State Relaxation of a Metalloporphyrin Revealed by Femtosecond X-ray Absorption Spectroscopy.

    PubMed

    Shelby, Megan L; Lestrange, Patrick J; Jackson, Nicholas E; Haldrup, Kristoffer; Mara, Michael W; Stickrath, Andrew B; Zhu, Diling; Lemke, Henrik T; Chollet, Matthieu; Hoffman, Brian M; Li, Xiaosong; Chen, Lin X

    2016-07-20

    Photoexcited Nickel(II) tetramesitylporphyrin (NiTMP), like many open-shell metalloporphyrins, relaxes rapidly through multiple electronic states following an initial porphyrin-based excitation, some involving metal centered electronic configuration changes that could be harnessed catalytically before excited state relaxation. While a NiTMP excited state present at 100 ps was previously identified by X-ray transient absorption (XTA) spectroscopy at a synchrotron source as a relaxed (d,d) state, the lowest energy excited state (J. Am. Chem. Soc., 2007, 129, 9616 and Chem. Sci., 2010, 1, 642), structural dynamics before thermalization were not resolved due to the ∼100 ps duration of the available X-ray probe pulse. Using the femtosecond (fs) X-ray pulses of the Linac Coherent Light Source (LCLS), the Ni center electronic configuration from the initial excited state to the relaxed (d,d) state has been obtained via ultrafast Ni K-edge XANES (X-ray absorption near edge structure) on a time scale from hundreds of femtoseconds to 100 ps. This enabled the identification of a short-lived Ni(I) species aided by time-dependent density functional theory (TDDFT) methods. Computed electronic and nuclear structure for critical excited electronic states in the relaxation pathway characterize the dependence of the complex's geometry on the electron occupation of the 3d orbitals. Calculated XANES transitions for these excited states assign a short-lived transient signal to the spectroscopic signature of the Ni(I) species, resulting from intramolecular charge transfer on a time scale that has eluded previous synchrotron studies. These combined results enable us to examine the excited state structural dynamics of NiTMP prior to thermal relaxation and to capture intermediates of potential photocatalytic significance.

  16. Effect of xanthophyll composition on the chlorophyll excited state lifetime in plant leaves and isolated LHCII

    NASA Astrophysics Data System (ADS)

    Johnson, Matthew P.; Zia, Ahmad; Horton, Peter; Ruban, Alexander V.

    2010-07-01

    Xanthophyll excited states have been implicated by transient absorption and two-photon excitation studies in playing a key role in the regulation of photosynthetic light harvesting via photoprotective energy dissipation. For any proposed quenching mechanism to be effective it must reduce the chlorophyll excited state lifetime from 2 ns to ˜0.5-0.4 ns. In the presented study the effect of xanthophyll composition on the chlorophyll excited state lifetime in Arabidopsis leaves in the light harvesting ( F m) and photoprotective (NPQ) states was determined. The data was compared to the chlorophyll excited state lifetime of native isolated LHCII and CP26 in detergent micelles with varying xanthophyll composition. It was found that although the differences in xanthophyll composition between LHC complexes from various Arabidopsis mutants were sufficient to explain the varying F m lifetime (and varying PSII efficiency), they were not of a sufficient scale to fully explain the observed differences in the NPQ lifetimes. Only when the LHC complexes were exposed to a low detergent/low pH media, a condition known to mimic the conformational state of LHCII associated with NPQ in vivo, were variations in excited state lifetime large enough to explain the differences observed in leaves. Furthermore, the data reveal that the replacement of lutein by either zeaxanthin or violaxanthin in the internal xanthophyll binding sites of LHCII and CP26 reduces the efficiency of energy dissipation in the photoprotective state in leaves and isolated complexes.

  17. Slow Intramolecular Vibrational Relaxation Leads to Long-Lived Excited-State Wavepackets.

    PubMed

    Rafiq, Shahnawaz; Scholes, Gregory D

    2016-09-01

    Broadband optical pump and compressed white light continuum probe were used to measure the transient excited-state absorption, ground-state bleach, and stimulated emission signals of cresyl violet solution in methanol. Amplitude oscillations caused by wavepacket motion in the ground and excited electronic states were analyzed. It was found that vibrational coherences in the excited state persist for more than the experimental waiting time window of 6 ps, and the strongest mode had a dephasing time constant of 2.4 ps. We hypothesize the dephasing of the wavepacket in the excited state is predominantly caused by intramolecular vibrational relaxation (IVR). Slow IVR indicates weak mode-mode coupling and therefore weak anharmonicity of the potential of this vibration. Thus, the initially prepared vibrational wavepacket in the excited state is not significantly perturbed by nonadiabatic coupling to other electronic states, and hence the diabatic and adiabatic representations of the system are essentially identical within the Born-Oppenheimer approximation. The wavepacket therefore evolves with time in an almost harmonic potential, slowly dephased by IVR and the pure vibrational decoherence. The consistency in the position of node (phase change in the wavepacket) in the excited-state absorption and stimulated emission signals without undergoing any frequency shift until the wavepacket is completely dephased conforms to the absence of any reactive internal conversion. PMID:27510098

  18. Slow Intramolecular Vibrational Relaxation Leads to Long-Lived Excited-State Wavepackets.

    PubMed

    Rafiq, Shahnawaz; Scholes, Gregory D

    2016-09-01

    Broadband optical pump and compressed white light continuum probe were used to measure the transient excited-state absorption, ground-state bleach, and stimulated emission signals of cresyl violet solution in methanol. Amplitude oscillations caused by wavepacket motion in the ground and excited electronic states were analyzed. It was found that vibrational coherences in the excited state persist for more than the experimental waiting time window of 6 ps, and the strongest mode had a dephasing time constant of 2.4 ps. We hypothesize the dephasing of the wavepacket in the excited state is predominantly caused by intramolecular vibrational relaxation (IVR). Slow IVR indicates weak mode-mode coupling and therefore weak anharmonicity of the potential of this vibration. Thus, the initially prepared vibrational wavepacket in the excited state is not significantly perturbed by nonadiabatic coupling to other electronic states, and hence the diabatic and adiabatic representations of the system are essentially identical within the Born-Oppenheimer approximation. The wavepacket therefore evolves with time in an almost harmonic potential, slowly dephased by IVR and the pure vibrational decoherence. The consistency in the position of node (phase change in the wavepacket) in the excited-state absorption and stimulated emission signals without undergoing any frequency shift until the wavepacket is completely dephased conforms to the absence of any reactive internal conversion.

  19. The Millimeter-Wave Spectrum of Methacrolein. Torsion-Rotation Effects in the Excited States

    NASA Astrophysics Data System (ADS)

    Zakharenko, Olena; Motiyenko, R. A.; Aviles Moreno, Juan-Ramon; Huet, T. R.

    2015-06-01

    Last year we reported the analysis of the rotational spectrum of s-trans conformer of methacrolein CH2=C(CH3)CHO in the ground vibrational state. In this talk we report the study of its low lying excited vibrational states. The study is based on room-temperature absorption spectra of methacrolein recorded in the frequency range 150 - 465 GHz using the spectrometer in Lille. The new results include assignment of the first excited torsional state (131 cm-1), and the joint analysis of the vt = 0 and vt = 1 states, that allowed us to improve the model in the frame of Rho-Axis-Method (RAM) Hamiltonian and to remove some strong correlations between parameters. Also we assigned the first excited vibrational state of the skeletal torsion mode (170 cm-1). The inverse sequence of A and E tunneling substates as well as anomalous A-E splittings observed for the rotational lines of vsk = 1 state clearly indicate a coupling between methyl torsion and skeletal torsion. However we were able to fit within experimental accuracy the rotational lines of vsk = 1 state using the RAM Hamiltonian. Because of the inversion of the A and E tunneling substates the rotational lines of the vsk = 1 states were assumed to belong to a virtual first excited torsional state. Finally, we assigned several low-Ka rotational transitions of the excited vibrational states above 200 cm-1 but their analysis is complicated by different rotation-vibration interactions. In particular there is an evidence of the Fermi-type resonance between the second excited torsional state and the first excited state of the in-plane skeletal bending mode (265 cm-1). Support from the French Laboratoire d'Excellence CaPPA (Chemical and Physical Properties of the Atmosphere) through contract ANR-10-LABX-0005 of the Programme d'Investissements d'Avenir is acknowledged. Zakharenko O. et al., 69th ISMS, 2014, TI01

  20. Permanent Magnet Synchronous Condenser with Solid State Excitation

    SciTech Connect

    Hsu, Ping; Muljadi, Eduard; Wu, Ziping; Gao, Wenzhong

    2015-10-05

    A synchronous condenser consists of a free-spinning wound-field synchronous generator and a field excitation controller. In this paper, we propose a synchronous generator that employs a permanent magnet synchronous generator (PMSG) instead of a wound-field machine. PMSGs have the advantages of higher efficiency and reliability. In the proposed configuration, the reactive power control is achieved by a voltage source converter connected in series with the PMSG and the grid. The converter varies the phase voltage of the PMSG so as to create the same effect of over or under excitation in a wound-field machine. The converter output voltage level controls the amount and the direction of the produced reactive power and the voltage's phase is kept in-phase with the grid voltage except a slight phase can be introduced so that some power can be drawn from the grid for maintaining the DC bus voltage level of the converter. Since the output voltage of the converter is only a fraction of the line voltage, its VA rating is only a fraction of the rating of the PMSG. The proposed scheme is shown to be effective by computer simulation.

  1. Excited-State Coordination Chemistry: Excited-State Basicity of Bis(2,2'-bipyridyl)(2,3-dipyridylpyrazine)ruthenium(II)

    NASA Astrophysics Data System (ADS)

    Zambrana, José L.; Ferloni, Elena X.; Gafney, Harry D.

    2009-10-01

    The proton dependencies of the absorption and emission spectra of bis(2,2'-bipyridyl)(2,3-bis(2-pyridyl)pyrazine)ruthenium(II), (bpy)2Ru(dpp)2+ indicate that population of the dpp-localized MLCT state increases the basicity of dpp peripheral nitrogens. NMR spectra reveal the protonation of the peripheral dpp pyridine in the ground state, pKa of 1.12 ± 0.03, occurs intermediate between the changes evident in the absorption and emission spectra. As a result, the emissivity of aqueous solutions of (bpy)2Ru(dpp)2+ as a function of [H+] derives from two emissive species: the unprotonated complex and the monoprotonated complex [(bpy)2Ru(dppHpy)]3+ with the proton attached to the peripheral dpp pyridine. Although protonation in the MLCT state generally quenches the emission, the emissivity of the monoprotonated complex, albeit weak, is attributed to the asymmetric distribution of the charge in the MLCT state. The majority of the transferred charge resides at the peripheral pyrazinyl nitrogen, and excited-state acid-base chemistry occurs predominantly at this site. Nonetheless, ground-state protonation of the peripheral dpp pyridine dramatically increases the nonradiative decay rate and significantly influences subsequent excited-state protonation processes. Protonation of the excited state changes from a bimolecular process to a combination of inter- and intramolecular processes where the proton transfers from the dpp pyridyl nitrogen to the dpp pyrazinyl nitrogen and from the surrounding aqueous solvent shell. Energetically, changes in the absorption spectra originally attributed to the first protonation of the complex and from which the ΔpKa of the excited state have been estimated, in fact, correspond to the second protonation of the complex.

  2. Ultrafast excited state dynamics of S2 and S1 states of triphenylmethane dyes.

    PubMed

    Singhal, Pallavi; Ghosh, Hirendra N

    2014-08-21

    Excited state dynamics of S2 and S1 states for a series of TPM dyes, pyrogallol red (PGR), bromopyrogallol red (Br-PGR) and aurin tricarboxylic acid (ATC), have been monitored by using ultrafast transient absorption and fluorescence up-conversion techniques. Optical absorption studies indicate that all the TPM dyes exist as keto-enol tautomers depending upon the pH of the solution. Interestingly, all the TPM dyes give S2 emission (major emitting state) in addition to weak S1 emission. S2 emission lifetimes as fast as ∼150-300 fs and S1 emission lifetimes of 2-5 ns were observed depending upon the molecular structure of the dyes. Femtosecond transient absorption studies suggest the presence of an ultrafast non-radiative decay channel from the S2 state in addition to S2 luminescence. The vibrational relaxation time from hot S1 state is found to be 2-6 ps. The heavy atom effect has been observed in ultrafast relaxation dynamics of Br-PGR.

  3. Multiple-Resonance Local Wave Functions for Accurate Excited States in Quantum Monte Carlo.

    PubMed

    Zulfikri, Habiburrahman; Amovilli, Claudio; Filippi, Claudia

    2016-03-01

    We introduce a novel class of local multideterminant Jastrow-Slater wave functions for the efficient and accurate treatment of excited states in quantum Monte Carlo. The wave function is expanded as a linear combination of excitations built from multiple sets of localized orbitals that correspond to the bonding patterns of the different Lewis resonance structures of the molecule. We capitalize on the concept of orbital domains of local coupled-cluster methods, which is here applied to the active space to select the orbitals to correlate and construct the important transitions. The excitations are further grouped into classes, which are ordered in importance and can be systematically included in the Jastrow-Slater wave function to ensure a balanced description of all states of interest. We assess the performance of the proposed wave function in the calculation of vertical excitation energies and excited-state geometry optimization of retinal models whose π → π* state has a strong intramolecular charge-transfer character. We find that our multiresonance wave functions recover the reference values of the total energies of the ground and excited states with only a small number of excitations and that the same expansion can be flexibly used at very different geometries. Furthermore, significant computational saving can also be gained in the orbital optimization step by selectively mixing occupied and virtual orbitals based on spatial considerations without loss of accuracy on the excitation energy. Our multiresonance wave functions are therefore compact, accurate, and very promising for the calculation of multiple excited states of different character in large molecules.

  4. Switching between ground and excited states by optical feedback in a quantum dot laser diode

    SciTech Connect

    Virte, Martin; Breuer, Stefan; Sciamanna, Marc; Panajotov, Krassimir

    2014-09-22

    We demonstrate switching between ground state and excited state emission in a quantum-dot laser subject to optical feedback. Even though the solitary laser emits only from the excited state, we can trigger the emission of the ground state by optical feedback. We observe recurrent but incomplete switching between the two emission states by variation of the external cavity length in the sub-micrometer scale. We obtain a good qualitative agreement of experimental results with simulation results obtained by a rate equation that accounts for the variations of the feedback phase.

  5. Counting the number of excited states in organic semiconductor systems using topology

    SciTech Connect

    Catanzaro, Michael J.; Shi, Tian; Tretiak, Sergei; Chernyak, Vladimir Y.

    2015-02-28

    Exciton scattering theory attributes excited electronic states to standing waves in quasi-one-dimensional molecular materials by assuming a quasi-particle picture of optical excitations. The quasi-particle properties at branching centers are described by the corresponding scattering matrices. Here, we identify the topological invariant of a scattering center, referred to as its winding number, and apply topological intersection theory to count the number of quantum states in a quasi-one-dimensional system.

  6. Counting the number of excited states in organic semiconductor systems using topology.

    PubMed

    Catanzaro, Michael J; Shi, Tian; Tretiak, Sergei; Chernyak, Vladimir Y

    2015-02-28

    Exciton scattering theory attributes excited electronic states to standing waves in quasi-one-dimensional molecular materials by assuming a quasi-particle picture of optical excitations. The quasi-particle properties at branching centers are described by the corresponding scattering matrices. Here, we identify the topological invariant of a scattering center, referred to as its winding number, and apply topological intersection theory to count the number of quantum states in a quasi-one-dimensional system. PMID:25725718

  7. An Efficient Variational Principle for the Direct Optimization of Excited States.

    PubMed

    Zhao, Luning; Neuscamman, Eric

    2016-08-01

    We present a variational principle that enables systematically improvable predictions for individual excited states through an efficient Monte Carlo evaluation. We demonstrate its compatibility with different ansatzes and with both real space and Fock space sampling and discuss its potential for use in the solid state. In numerical demonstrations for challenging molecular excitations, the method rivals or surpasses the accuracy of very high level methods using drastically more compact wave function approximations. PMID:27379468

  8. Excited states of154Nd studied through the decay of154Pr

    NASA Astrophysics Data System (ADS)

    Toh, Y.; Okano, K.; Taniguchi, A.; Yamada, S.; Kawase, Y.

    1996-12-01

    The neutron-rich isotope154Pr, the heaviest isotope of praseodymium, has been investigated by γ-ray multispectrum scaling and γ-γ-(t), X-γ-(t) coincidence experiments. The isotope154Pr was separated from235U fission products with the on-line isotope separator KUR-ISOL. The decay scheme of154Pr has been constructed consisting of 9 excited states and 12 transitions in154Nd, including 7 excited states newly found in the present experiment.

  9. Excited-state dynamics of guanosine in aqueous solution revealed by time-resolved photoelectron spectroscopy: experiment and theory.

    PubMed

    Buchner, Franziska; Heggen, Berit; Ritze, Hans-Hermann; Thiel, Walter; Lübcke, Andrea

    2015-12-21

    Time-resolved photoelectron spectroscopy is performed on aqueous guanosine solution to study its excited-state relaxation dynamics. Experimental results are complemented by surface hopping dynamic simulations and evaluation of the excited-state ionization energy by Koopmans' theorem. Two alternative models for the relaxation dynamics are discussed. The experimentally observed excited-state lifetime is about 2.5 ps if the molecule is excited at 266 nm and about 1.1 ps if the molecule is excited at 238 nm. The experimental probe photon energy dependence of the photoelectron kinetic energy distribution suggests that the probe step is not vertical and involves a doubly-excited autoionizing state.

  10. Intersystem crossing from highly excited states. rhodamine 6G

    SciTech Connect

    Ryl'kov, V.V.; Cheshev, E.A.

    1985-09-01

    The authors carried out an investigation of ethanolic solutions of Rhodamine 6G (R6G) at 20 C by laser flash photolysis. The excitation of dilute (3 /SUP ./ 10/sup -5/ M) solutions of R6G with an initial optical density of 1.5 up to an intensity of 100 MW/cm/sup 2/ resulted in only weak triplet-triplet absorption. The introduction of additions of lithium chloride or lithium bromide in 0.1 M concentrations into a solution of R6G (3.10/sup -5/ M) resulted in the appearance of induced absorption and the introduction of an addition of lithium nitrate in the same concentration into the solution did not result in enhancement of triplet-triplet absorption.

  11. Steady-state photoluminescent excitation characterization of semiconductor carrier recombination.

    PubMed

    Bhosale, J S; Moore, J E; Wang, X; Bermel, P; Lundstrom, M S

    2016-01-01

    Photoluminescence excitation spectroscopy is a contactless characterization technique that can provide valuable information about the surface and bulk recombination parameters of a semiconductor device, distinct from other sorts of photoluminescent measurements. For this technique, a temperature-tuned light emitting diode (LED) has several advantages over other light sources. The large radiation density offered by LEDs from near-infrared to ultraviolet region at a low cost enables efficient and fast photoluminescence measurements. A simple and inexpensive LED-based setup facilitates measurement of surface recombination velocity and bulk Shockley-Read-Hall lifetime, which are key parameters to assess device performance. Under the right conditions, this technique can also provide a contactless way to measure the external quantum efficiency of a solar cell. PMID:26827306

  12. Steady-state photoluminescent excitation characterization of semiconductor carrier recombination

    NASA Astrophysics Data System (ADS)

    Bhosale, J. S.; Moore, J. E.; Wang, X.; Bermel, P.; Lundstrom, M. S.

    2016-01-01

    Photoluminescence excitation spectroscopy is a contactless characterization technique that can provide valuable information about the surface and bulk recombination parameters of a semiconductor device, distinct from other sorts of photoluminescent measurements. For this technique, a temperature-tuned light emitting diode (LED) has several advantages over other light sources. The large radiation density offered by LEDs from near-infrared to ultraviolet region at a low cost enables efficient and fast photoluminescence measurements. A simple and inexpensive LED-based setup facilitates measurement of surface recombination velocity and bulk Shockley-Read-Hall lifetime, which are key parameters to assess device performance. Under the right conditions, this technique can also provide a contactless way to measure the external quantum efficiency of a solar cell.

  13. Highly excited {Sigma}{sup -} states of molecular hydrogen

    SciTech Connect

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

    2011-05-15

    We report calculations of H{sub 2} {Sigma}{sup -} states using a variational R-matrix approach combined with multichannel quantum defect theory. Several Rydberg series converging to the 2p{pi} state of the H{sub 2}{sup +} ion core are established and their mutual channel interactions characterized. The influence of the external electron on the chemical bond is found to be particularly strong in these electronically and chemically weakly bound states.

  14. Non-orthogonal configuration interaction for the calculation of multielectron excited states

    NASA Astrophysics Data System (ADS)

    Sundstrom, Eric J.; Head-Gordon, Martin

    2014-03-01

    We apply Non-orthogonal Configuration Interaction (NOCI) to molecular systems where multielectron excitations, in this case double excitations, play a substantial role: the linear polyenes and β-carotene. We demonstrate that NOCI when applied to systems with extended conjugation, provides a qualitatively correct wavefunction at a fraction of the cost of many other multireference treatments. We also present a new extension to this method allowing for purification of higher-order spin states by utilizing Generalized Hartree-Fock Slater determinants and the details for computing ⟨S2⟩ for the ground and excited states.

  15. Yields of excited states of solutes in irradiated benzene and cyclohexane

    SciTech Connect

    Choi, H.T.; Hirayama, F.; Lipsky, S.

    1984-09-13

    The yields of lowest excited singlet states of diphenyloxazole and p-terphenyl in benzene and of diphenyloxazole, p-terphenyl, and biphenyl in cyclohexane have been measured for excitation by using /sup 85/Kr ..beta.. particles. The dependence of the yield on solute concentration for benzene solutions is shown to be accurately represented by a Stern-Volmer function from 5 x 10/sup -4/ to 10/sup -2/ M and to extrapolate at infinite solute concentration to the yield of excited singlet states of neat liquid benzene. The presence of oxygen in the solution does not affect the extrapolation. The absolute efficiencies of energy transfer from irradiated benzene to the solutes are in good agreement with previous measurements made by using optical excitation below the ionization threshold. These results provide additional confirmation that the mechanism of formation of excited solute states in fast-electron-irradiated benzene does not significantly involve electron or hole capture by the solute. They also demonstrate that the inhomogeneity of energy deposition does not affect the ratio of probabilities of the decay of excited benzene by photon emission to its decay by nonradiative energy transfer to the solute. For cyclohexane solutions, it is confirmed that the yields of excited solute states are lower than in benzene solutions at comparable concentration, but larger than would be expected were the same nonionic mechanism to apply as it does in benzene. The consequences of these conclusions are discussed.

  16. State-resolved collisional relaxation of highly vibrationally excited CsH by CO2.

    PubMed

    Mu, Baoxia; Cui, Xiuhua; Shen, Yifan; Dai, Kang

    2015-09-01

    Quenching of highly vibrationally excited CsH(X(1)Σ(+), v=15-23) by collisions with CO2 was investigated. A significant fraction of the initial population of highly vibrationally excited CsH(v=22) was relaxed to a low vibrational level (Δv=-5). The near-resonant 5-1 vibration-to-vibration (V-V) energy was efficiently exchanged. The rate constants for the rotational levels of CO2(00(0)0) [J=36-60] and CO2(00(0)1) [J=5-31] from the collisions with excited CsH were determined. The experiments revealed that the collisions resulting in CO2(00(0)0) were accompanied by substantial excitation in rotation and translation. The vibrationally excited CO2(00(0)1) state exhibited rotational and translational energy distributions near those of the initial state. The total quenching rates relative to the probed state of excited CsH were determined for both CO2 states. The corresponding data indicated that the gains in the rotational and translational energies in CO2 were sensitive to the collisional depletion of excited CsH.

  17. Excited state absorption properties of Pt(II) terpyridyl complexes bearing π-conjugated arylacetylides.

    PubMed

    Wang, Xianghuai; Goeb, Sébastien; Ji, Zhiqiang; Castellano, Felix N

    2010-11-18

    The synthesis, photophysics, and excited state absorption properties of three platinum(II) terpyridyl acetylide charge transfer (CT) complexes possessing a lone ancillary ligand systematically varied in phenylacetylide (PA) π-conjugation length, [Pt((t)Bu(3)tpy)([C≡C-C(6)H(4)](n)-H)]ClO(4) (n = 1, 2, 3), are described. Density functional theory (DFT) calculations performed on the ground states of complexes 1, 2, and 3 reveal that their HOMOs reside mainly on the ancillary π-conjugated PA moiety, ranging from 86 to 97%, with LUMOs predominantly centered on the terpyridyl acceptor ligand (91-92%). This electronic structure leads to the production of a triplet ligand-to-ligand CT ((3)LLCT) excited state upon visible light excitation with minor contributions from the corresponding triplet metal-to-ligand CT ((3)MLCT) excited state. Unusually strong red-to-near-IR transient absorptions are produced in the excited states of these molecules following selective long wavelength visible excitation of the low energy CT bands that do not emanate from the terpyridyl radical anion produced in the CT excited state or from an arylacetylide-based triplet intraligand ((3)IL) excited state. The extinction coefficients of these low energy absorption transients were determined using the energy transfer method with anthracene serving as the triplet acceptor. A detailed theoretical investigation using DFT and TDDFT methods reveals that these intense near-IR transient absorptions involve transitions resulting from transient oxidation of the PA subunit. In essence, the production of the (3)LLCT excited state transiently oxidizes the PA moiety by one electron, producing the corresponding highly absorbing radical cation-like species, analogous to that experienced in related intramolecular photoinduced electron transfer reactions. The computational work successfully predicts the oscillator strength and peak wavelength of the measured excited state absorption transients across this series

  18. Excited state evolution towards ligand loss and ligand chelation at group 6 metal carbonyl centres.

    PubMed

    Manton, Jennifer C; Amirjalayer, Saeed; Coleman, Anthony C; McMahon, Suzanne; Harvey, Emma C; Greetham, Gregory M; Clark, Ian P; Buma, Wybren Jan; Woutersen, Sander; Pryce, Mary T; Long, Conor

    2014-12-21

    The photochemistry and photophysics of three model "half-sandwich" complexes (η(6)-benzophenone)Cr(CO)3, (η(6)-styrene)Cr(CO)3, and (η(6)-allylbenzene)Cr(CO)3 were investigated using pico-second time-resolved infrared spectroscopy and time-dependent density functional theory methods. The (η(6)-benzophenone)Cr(CO)3 complex was studied using two excitation wavelengths (470 and 320 nm) while the remaining complexes were irradiated using 400 nm light. Two independent excited states were detected spectroscopically for each complex, one an unreactive excited state of metal-to-arene charge-transfer character and the other with metal-to-carbonyl charge transfer character. This second excited state leads to an arrested release of CO on the pico-second time-scale. Low-energy excitation (470 nm) of (η(6)-benzophenone)Cr(CO)3 populated only the unreactive excited state which simply relaxes to the parent complex. Higher energy irradiation (320 nm) induced CO-loss. Irradiation of (η(6)-styrene)Cr(CO)3, or (η(6)-allylbenzene)Cr(CO)3 at 400 nm provided evidence for the simultaneous population of both the reactive and unreactive excited states. The efficiency at which the unreactive excited state is populated depends on the degree of conjugation of the substituent with the arene π-system and this affects the efficiency of the CO-loss process. The quantum yield of CO-loss is 0.50 for (η(6)-allylbenzene)Cr(CO)3 and 0.43 for (η(6)-styrene)Cr(CO)3. These studies provide evidence for the existence of two photophysical routes to CO loss, a minor ultrafast route and an arrested mechanism involving the intermediate population of a reactive excited state. This reactive excited state either relaxes to reform the parent species or eject CO. Thus the quantum yield of the CO-loss is strongly dependent on the excitation wavelength. Time-dependent density functional theory calculations confirm that the state responsible for ultrafast CO-loss has significant metal-centred character while

  19. Photochemistry of excited-state species in natural waters: a role for particulate organic matter.

    PubMed

    Cottrell, Barbara A; Timko, Stephen A; Devera, Lianne; Robinson, Alice K; Gonsior, Michael; Vizenor, Ashley E; Simpson, André J; Cooper, William J

    2013-09-15

    Laser flash photolysis (LFP) was used to characterize a triplet excited state species isolated from Black River and San Joaquin wetlands particulate organic matter (POM). The solubilized organic matter, isolated from POM by pH-independent diffusion in distilled water, was named PdOM. UV-visible absorption spectroscopy, excitation-emission matrix spectroscopy (EEMs), and (1)H NMR were used to characterize the PdOM. While LFP of dissolved organic matter (DOM) is known to generate the solvated electron, LFP of the PdOM transient in argon-, air-, and nitrous oxide-saturated solutions indicated that this was a triplet excited state species ((3)PdOM*). The lifetime and the reactivity of (3)PdOM* with sorbic acid, a triplet state quencher, were compared with that of the triplet excited state of benzophenone, a DOM proxy. A second excited state species (designated DOM*), with a longer lifetime, was reported in a number of previous studies but not characterized. The lifetime of DOM*, measured for seventeen organic matter isolates, lignin, tannic acid, and three wetlands plant extracts, was shown to differentiate allochthonous from autochthonous DOM. (3)POM* and DOM* were also observed in lake water and a constructed wetlands' water. Aqueous extracts of fresh and aged plant material from the same wetland were shown to be one source of these excited state species. This study provides evidence of a role for POM in the photochemistry of natural and constructed wetland waters.

  20. Size and shape dependent photoluminescence and excited state decay rates of diamondoids.

    PubMed

    Richter, Robert; Wolter, David; Zimmermann, Tobias; Landt, Lasse; Knecht, Andre; Heidrich, Christoph; Merli, Andrea; Dopfer, Otto; Reiss, Philipp; Ehresmann, Arno; Petersen, Jens; Dahl, Jeremy E; Carlson, Robert M K; Bostedt, Christoph; Möller, Thomas; Mitric, Roland; Rander, Torbjörn

    2014-02-21

    We present photoluminescence spectra and excited state decay rates of a series of diamondoids, which represent molecular structural analogues to hydrogen-passivated bulk diamond. Specific isomers of the five smallest diamondoids (adamantane-pentamantane) have been brought into the gas phase and irradiated with synchrotron radiation. All investigated compounds show intrinsic photoluminescence in the ultraviolet spectral region. The emission spectra exhibit pronounced vibrational fine structure which is analyzed using quantum chemical calculations. We show that the geometrical relaxation of the first excited state of adamantane, exhibiting Rydberg character, leads to the loss of Td symmetry. The luminescence of adamantane is attributed to a transition from the delocalized first excited state into different vibrational modes of the electronic ground state. Similar geometrical changes of the excited state structure have also been identified in the other investigated diamondoids. The excited state decay rates show a clear dependence on the size of the diamondoid, but are independent of the particle geometry, further indicating a loss of particle symmetry upon electronic excitation.

  1. Size and shape dependent photoluminescence and excited state decay rates of diamondoids.

    PubMed

    Richter, Robert; Wolter, David; Zimmermann, Tobias; Landt, Lasse; Knecht, Andre; Heidrich, Christoph; Merli, Andrea; Dopfer, Otto; Reiss, Philipp; Ehresmann, Arno; Petersen, Jens; Dahl, Jeremy E; Carlson, Robert M K; Bostedt, Christoph; Möller, Thomas; Mitric, Roland; Rander, Torbjörn

    2014-02-21

    We present photoluminescence spectra and excited state decay rates of a series of diamondoids, which represent molecular structural analogues to hydrogen-passivated bulk diamond. Specific isomers of the five smallest diamondoids (adamantane-pentamantane) have been brought into the gas phase and irradiated with synchrotron radiation. All investigated compounds show intrinsic photoluminescence in the ultraviolet spectral region. The emission spectra exhibit pronounced vibrational fine structure which is analyzed using quantum chemical calculations. We show that the geometrical relaxation of the first excited state of adamantane, exhibiting Rydberg character, leads to the loss of Td symmetry. The luminescence of adamantane is attributed to a transition from the delocalized first excited state into different vibrational modes of the electronic ground state. Similar geometrical changes of the excited state structure have also been identified in the other investigated diamondoids. The excited state decay rates show a clear dependence on the size of the diamondoid, but are independent of the particle geometry, further indicating a loss of particle symmetry upon electronic excitation. PMID:24398975

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

    SciTech Connect

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

    2011-01-13

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

  3. First-order derivative couplings between excited states from adiabatic TDDFT response theory

    SciTech Connect

    Ou, Qi; Subotnik, Joseph E.; Bellchambers, Gregory D.; Furche, Filipp

    2015-02-14

    We present a complete derivation of derivative couplings between excited states in the framework of adiabatic time-dependent density functional response theory. Explicit working equations are given and the resulting derivative couplings are compared with derivative couplings from a pseudo-wavefunction ansatz. For degenerate excited states, i.e., close to a conical intersection (CI), the two approaches are identical apart from an antisymmetric overlap term. However, if the difference between two excitation energies equals another excitation energy, the couplings from response theory exhibit an unphysical divergence. This spurious behavior is a result of the adiabatic or static kernel approximation of time-dependent density functional theory leading to an incorrect analytical structure of the quadratic response function. Numerical examples for couplings close to a CI and for well-separated electronic states are given.

  4. Emergence of nontrivial magnetic excitations in a spin-liquid state of kagomé volborthite.

    PubMed

    Watanabe, Daiki; Sugii, Kaori; Shimozawa, Masaaki; Suzuki, Yoshitaka; Yajima, Takeshi; Ishikawa, Hajime; Hiroi, Zenji; Shibauchi, Takasada; Matsuda, Yuji; Yamashita, Minoru

    2016-08-01

    When quantum fluctuations destroy underlying long-range ordered states, novel quantum states emerge. Spin-liquid (SL) states of frustrated quantum antiferromagnets, in which highly correlated spins fluctuate down to very low temperatures, are prominent examples of such quantum states. SL states often exhibit exotic physical properties, but the precise nature of the elementary excitations behind such phenomena remains entirely elusive. Here, we use thermal Hall measurements that can capture the unexplored property of the elementary excitations in SL states, and report the observation of anomalous excitations that may unveil the unique features of the SL state. Our principal finding is a negative thermal Hall conductivity [Formula: see text] which the charge-neutral spin excitations in a gapless SL state of the 2D kagomé insulator volborthite Cu3V2O7(OH)2[Formula: see text]2H2O exhibit, in much the same way in which charged electrons show the conventional electric Hall effect. We find that [Formula: see text] is absent in the high-temperature paramagnetic state and develops upon entering the SL state in accordance with the growth of the short-range spin correlations, demonstrating that [Formula: see text] is a key signature of the elementary excitation formed in the SL state. These results suggest the emergence of nontrivial elementary excitations in the gapless SL state which feel the presence of fictitious magnetic flux, whose effective Lorentz force is found to be less than 1/100 of the force experienced by free electrons. PMID:27439874

  5. Control of multiple excited image states around segmented carbon nanotubes

    SciTech Connect

    Knörzer, J. Fey, C.; Sadeghpour, H. R.; Schmelcher, P.

    2015-11-28

    Electronic image states around segmented carbon nanotubes can be confined and shaped along the nanotube axis by engineering the image potential. We show how several such image states can be prepared simultaneously along the same nanotube. The inter-electronic distance can be controlled a priori by engineering tubes of specific geometries. High sensitivity to external electric and magnetic fields can be exploited to manipulate these states and their mutual long-range interactions. These building blocks provide access to a new kind of tailored interacting quantum systems.

  6. Control of multiple excited Rydberg states around segmented carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Schmelcher, Peter; Sadeghpour, Hossein; Knoerzer, Johannes; Fey, Christian

    2016-05-01

    Electronic image Rydberg states around segmented carbon nanotubes can be confined and shaped along the nanotube axis by engineering the image potential. We show how several such image states can be prepared simultaneously along the same nanotube. The inter-electronic distance can be controlled a priori by engineering tubes of specific geometries. High sensitivity to external electric and magnetic fields can be exploited to manipulate these states and their mutual long-range interactions. These building blocks provide access to a new kind of tailored long-range interacting quantum systems.

  7. Multireference general-model-space state-universal and state-specific coupled-cluster approaches to excited states

    NASA Astrophysics Data System (ADS)

    Li, Xiangzhu; Paldus, Josef

    2010-11-01

    The concept of C-conditions, originally introduced in the framework of the multireference (MR), general-model-space (GMS), state-universal (SU), coupled-cluster (CC) approach with singles and doubles (GMS-SU-CCSD) to account for the internal amplitudes that vanish in the case of a complete model space, is applied to a state-selective or state-specific Mukherjee MR-CC method (MkCCSD). In contrast to the existing applications, the emphasis is on the description of excited states, particularly those belonging to the same symmetry species. The applicability of the C-conditions in all MR-SU-CC approaches is emphasized. Convergence problems encountered in the MkCCSD method when handling higher-lying states are pointed out. The performance of the GMS-SU-CCSD and MkCCSD methods is illustrated by considering low-lying vertical excitation energies of the ethylene molecule and para-benzyne diradical. A comparison with the equation-of-motion CCSD results, as well as with the available experimental data and recent multireference configuration interaction theoretical results, is also provided.

  8. Gapped excitations of unconventional fractional quantum Hall effect states in the second Landau level

    NASA Astrophysics Data System (ADS)

    Wurstbauer, U.; Levy, A. L.; Pinczuk, A.; West, K. W.; Pfeiffer, L. N.; Manfra, M. J.; Gardner, G. C.; Watson, J. D.

    2015-12-01

    We report the observation of low-lying collective charge and spin excitations in the second Landau level at ν =2 +1 /3 and also for the very fragile states at ν =2 +2 /5 and 2 +3 /8 in inelastic light scattering experiments. These modes exhibit a clear dependence on filling factor and temperature substantiating the unique access to the characteristic neutral excitation spectra of the incompressible fractional quantum Hall effect (FQHE) states. A detailed mode analysis reveals low-energy modes at around 70 μ eV and a sharp mode slightly below the Zeeman energy interpreted as gap and spin-wave excitation, respectively. The lowest-energy collective charge excitation spectrum at ν =2 +1 /3 exhibits significant qualitative similarities with its cousin state in the lowest Landau level at ν =1 /3 suggesting similar magnetoroton minima in the neutral excitations. The mode energies differ by a scaling of 0.15 indicating different interaction physics in the N =0 and N =1 Landau levels. The striking polarization dependence in elastic and inelastic light scattering is discussed in the framework of anisotropic electron phases that allow for the stabilization of nematic FQHE states. The observed excitation spectra provide new insights by accessing quantum phases in the bulk of electron systems and facilitate comparison with different theoretical descriptions of those enigmatic FQHE states.

  9. Excited-state structure of oligothiophene dendrimers: computational and experimental study.

    PubMed

    Badaeva, Ekaterina; Harpham, Michael R; Guda, Ramakrishna; Süzer, Özgün; Ma, Chang-Qi; Bäuerle, Peter; Goodson, Theodore; Tretiak, Sergei

    2010-12-01

    The nature of one and two-photon absorption enhancement in a series of oligothiophene dendrimers, recently proposed for applications in entangled photon sensors and solar cells, has been analyzed using both theory (time dependent density functional theory calculations) and experiment (fluorescence upconversion measurements). The linear absorption spectra exhibit a red shift of the absorption maxima and broadening as a function of dendrimer generations. The two-photon absorption cross sections increase sharply with the number of thiophene units in the dendrimer. The cooperative enhancement in absorption two-photon cross sections is explained by (i) an increase in the excited-state density for larger molecules and (ii) delocalization of the low-lying excited states over extended thiophene chains. Fluorescence anisotropy measurements and examination of the calculated excited-state properties reveal that this delocalization is accompanied by a size-dependent decrease in excited-state symmetries. A substantial red shift of the emission maxima for larger dendrimers is explained through the vibronic planarization of the longest linear α-thiophene chain for the emitting excited state. For higher generations, the fluorescence quantum yield decreases due to increased nonradiative decay efficiency (e.g., intersystem crossing). The detailed information about the dendrimer 3D structure and excitations provides guidance for further optimizations of dendritic structures for nonlinear optical and opto-electronic applications. PMID:21077602

  10. Collision-induced energy transfer in intermediate excited states of cesium

    NASA Astrophysics Data System (ADS)

    Lukaszewski, M.; Jackowska, I.

    1993-09-01

    We report an application of laser spectroscopy techniques to a study of collision-induced interactions in atomic excited states. Due to pulsed dye laser excitation a considerable selective population of highly excited states of ccsium is obtained. Collision-induced transfer of excitation energy between the excited states results in modifications in time and spectral characteristics of observed atomic fluorescence. Quantitative information on the efficiency of collisional processes can be obtained from the measurements of time constants of the time-resolved fluorescence signals and/or from those of the integrated intensities of the fluorescence lines. Both possibilities are used in the present work. Perturbation of nD (n=8-14) and nS (n=1O-15) states of cesium in collisions with noble-gas atoms is investigated. The cross sections for the transfer of excitation between fine-structure substates of the nD states (J mixing) and for the nS-(n-4)F intermultiplet transfer are obtained.

  11. The electronic origin and vibrational levels of the first excited singlet state of isocyanic acid (HNCO)

    SciTech Connect

    Berghout, H. Laine; Crim, F. Fleming; Zyrianov, Mikhail; Reisler, Hanna

    2000-04-15

    The combination of vibrationally mediated photofragment yield spectroscopy, which excites molecules prepared in single vibrational states, and multiphoton fluorescence spectroscopy, which excites molecules cooled in a supersonic expansion, provides detailed information on the energetics and vibrational structure of the first excited singlet state (S{sub 1}) of isocyanic acid (HNCO). Dissociation of molecules prepared in individual vibrational states by stimulated Raman excitation probes vibrational levels near the origin of the electronically excited state. Detection of fluorescence from dissociation products formed by multiphoton excitation through S{sub 1} of molecules cooled in a supersonic expansion reveals the vibrational structure at higher energies. Both types of spectra show long, prominent progressions in the N-C-O bending vibration built on states with different amounts of N-C stretching excitation and H-N-C bending excitation. Analyzing the spectra locates the origin of the S{sub 1} state at 32 449{+-}20 cm{sup -1} and determines the harmonic vibrational frequencies of the N-C stretch ({omega}{sub 3}=1034{+-}20 cm{sup -1}), the H-N-C bend ({omega}{sub 4}=1192{+-}19 cm{sup -1}), and the N-C-O bend ({omega}{sub 5}=599{+-}7 cm{sup -1}), values that are consistent with several ab initio calculations. The assigned spectra strongly suggest that the N-C stretching vibration is a promoting mode for internal conversion from S{sub 1} to S{sub 0}. (c) 2000 American Institute of Physics.

  12. Permanent Magnet Synchronous Condenser with Solid State Excitation: Preprint

    SciTech Connect

    Hsu, P.; Muljadi, E.; Wu, Z.; Gao, W.

    2015-04-07

    A typical synchronous condenser (SC) consists of a free-spinning, wound-field synchronous generator and a field excitation controller. In this paper, we propose an SC that employs a permanent magnet synchronous generator (PMSG) instead of a wound-field machine. PMSGs have the advantages of higher efficiency and reliability. In the proposed configuration, the reactive power control is achieved by a voltage converter controller connected in series to the PMSG. The controller varies the phase voltage of the PMSG and creates the same effect on the reactive power flow as that of an over- or underexcited wound-field machine. The controller’s output voltage magnitude controls the amount of the reactive power produced by the SC. The phase of the controller’s output is kept within a small variation from the grid voltage phase. This small phase variation is introduced so that a small amount of power can be drawn from the grid into the controller to maintain its DC bus voltage. Because the output voltage of the controller is only a fraction of the line voltage, its VA rating is only a fraction of the rating of the PMSG. The proposed scheme is shown to be effective by computer simulations.

  13. A general ansatz for constructing quasi-diabatic states in electronically excited aggregated systems

    SciTech Connect

    Liu, Wenlan; Köhn, Andreas; Lunkenheimer, Bernd; Settels, Volker; Engels, Bernd; Fink, Reinhold F.

    2015-08-28

    We present a general method for analyzing the character of singly excited states in terms of charge transfer (CT) and locally excited (LE) configurations. The analysis is formulated for configuration interaction singles (CIS) singly excited wave functions of aggregate systems. It also approximately works for the second-order approximate coupled cluster singles and doubles and the second-order algebraic-diagrammatic construction methods [CC2 and ADC(2)]. The analysis method not only generates a weight of each character for an excited state, but also allows to define the related quasi-diabatic states and corresponding coupling matrix elements. In the character analysis approach, we divide the target system into domains and use a modified Pipek-Mezey algorithm to localize the canonical MOs on each domain, respectively. The CIS wavefunction is then transformed into the localized basis, which allows us to partition the wavefunction into LE configurations within domains and CT configuration between pairs of different domains. Quasi-diabatic states are then obtained by mixing excited states subject to the condition of maximizing the weight of one single LE or CT configuration (localization in configuration space). Different aims of such a procedure are discussed, either the construction of pure LE and CT states for analysis purposes (by including a large number of excited states) or the construction of effective models for dynamics calculations (by including a restricted number of excited states). Applications are given to LE/CT mixing in π-stacked systems, charge-recombination matrix elements in a hetero-dimer, and excitonic couplings in multi-chromophoric systems.

  14. A general ansatz for constructing quasi-diabatic states in electronically excited aggregated systems.

    PubMed

    Liu, Wenlan; Lunkenheimer, Bernd; Settels, Volker; Engels, Bernd; Fink, Reinhold F; Köhn, Andreas

    2015-08-28

    We present a general method for analyzing the character of singly excited states in terms of charge transfer (CT) and locally excited (LE) configurations. The analysis is formulated for configuration interaction singles (CIS) singly excited wave functions of aggregate systems. It also approximately works for the second-order approximate coupled cluster singles and doubles and the second-order algebraic-diagrammatic construction methods [CC2 and ADC(2)]. The analysis method not only generates a weight of each character for an excited state, but also allows to define the related quasi-diabatic states and corresponding coupling matrix elements. In the character analysis approach, we divide the target system into domains and use a modified Pipek-Mezey algorithm to localize the canonical MOs on each domain, respectively. The CIS wavefunction is then transformed into the localized basis, which allows us to partition the wavefunction into LE configurations within domains and CT configuration between pairs of different domains. Quasi-diabatic states are then obtained by mixing excited states subject to the condition of maximizing the weight of one single LE or CT configuration (localization in configuration space). Different aims of such a procedure are discussed, either the construction of pure LE and CT states for analysis purposes (by including a large number of excited states) or the construction of effective models for dynamics calculations (by including a restricted number of excited states). Applications are given to LE/CT mixing in π-stacked systems, charge-recombination matrix elements in a hetero-dimer, and excitonic couplings in multi-chromophoric systems.

  15. Electron Impact Excitation of Xenon from the Ground State and the Metastable State to the 5p57p Levels

    NASA Astrophysics Data System (ADS)

    Chen, Zhan-Bin; Dong, Chen-Zhong; Xie, Lu-You; Jiang, Jun

    2014-03-01

    Electron impact excitation cross sections from the ground state and the lowest metastable state 5p56s J = 2 to the excited states of the 5p57p configuration of xenon are calculated systematically using the fully relativistic distorted wave method. Special attention is paid to the configuration interaction effects in the wave-function expansion of target states. The results are in good agreement with the recent experimental data by Jung et al. [Phys. Rev. A 80 (2009) 062708] over the measured energy range. These accurate theoretical results can be used in the modeling and diagnosis of plasmas containing xenon.

  16. Mechanistic photodecarboxylation of pyruvic acid: Excited-state proton transfer and three-state intersection

    SciTech Connect

    Chang, Xue-Ping; Fang, Qiu Cui, Ganglong

    2014-10-21

    Photodissociation dynamics of pyruvic acid experimentally differs from that of commonly known ketones. We have employed the complete active space self-consistent field and its multi-state second-order perturbation methods to study its photodissociation mechanism in the S{sub 0}, T{sub 1}, and S{sub 1} states. We have uncovered four nonadiabatic photodecarboxylation paths. (i) The S{sub 1} system relaxes via an excited-state intramolecular proton transfer (ESIPT) to a hydrogen-transferred tautomer, near which an S{sub 1}/S{sub 0} conical intersection funnels the S{sub 1} to S{sub 0} state. Then, some trajectories continue completing the decarboxylation reaction in the S{sub 0} state; the remaining trajectories via a reverse hydrogen transfer return to the S{sub 0} minimum, from which a thermal decarboxylation reaction occurs. (ii) Due to a small S{sub 1} −T{sub 1} energy gap and a large S{sub 1}/T{sub 1} spin-orbit coupling, an efficient S{sub 1} → T{sub 1} intersystem crossing process happens again near this S{sub 1}/S{sub 0} conical intersection. When decaying to T{sub 1} state, a direct photodecarboxylation proceeds. (iii) Prior to ESIPT, the S{sub 1} system first decays to the T{sub 1} state via an S{sub 1} → T{sub 1} intersystem crossing; then, the T{sub 1} system evolves to a hydrogen-transferred tautomer. Therefrom, an adiabatic T{sub 1} decarboxylation takes place due to a small barrier of 7.7 kcal/mol. (iv) Besides the aforementioned T{sub 1} ESIPT process, there also exists a comparable Norrish type I reaction in the T{sub 1} state, which forms the ground-state products of CH{sub 3}CO and COOH. Finally, we have found that ESIPT plays an important role. It closes the S{sub 1}-T{sub 1} and S{sub 1}-S{sub 0} energy gaps, effecting an S{sub 1}/T{sub 1}/S{sub 0} three-state intersection region, and mediating nonadiabatic photodecarboxylation reactions of pyruvic acid.

  17. Mid-infrared ultrafast laser pulses induced third harmonic generation in nitrogen molecules on an excited state

    PubMed Central

    Xie, Hongqiang; Li, Guihua; Yao, Jinping; Chu, Wei; Li, Ziting; Zeng, Bin; Wang, Zhanshan; Cheng, Ya

    2015-01-01

    We report on generation of third harmonic from nitrogen molecules on the excited state with a weak driver laser pulse at a mid-infrared wavelength. The excited nitrogen molecules are generated using a circularly polarized intense femtosecond pulse which produces energetic electrons by photoionization to realize collisional excitation of nitrogen molecules. Furthermore, since the third harmonic is generated using a pump-probe scheme, it enables investigation of the excited-state dynamics of nitrogen molecules produced under different conditions. We also perform a comparative investigation in excited argon atoms, revealing different decay dynamics of the molecules and atoms from the excited states in femtosecond laser induced filaments. PMID:26522886

  18. Mid-infrared ultrafast laser pulses induced third harmonic generation in nitrogen molecules on an excited state.

    PubMed

    Xie, Hongqiang; Li, Guihua; Yao, Jinping; Chu, Wei; Li, Ziting; Zeng, Bin; Wang, Zhanshan; Cheng, Ya

    2015-11-02

    We report on generation of third harmonic from nitrogen molecules on the excited state with a weak driver laser pulse at a mid-infrared wavelength. The excited nitrogen molecules are generated using a circularly polarized intense femtosecond pulse which produces energetic electrons by photoionization to realize collisional excitation of nitrogen molecules. Furthermore, since the third harmonic is generated using a pump-probe scheme, it enables investigation of the excited-state dynamics of nitrogen molecules produced under different conditions. We also perform a comparative investigation in excited argon atoms, revealing different decay dynamics of the molecules and atoms from the excited states in femtosecond laser induced filaments.

  19. Estimation of ground and excited state dipole moments of Oil Red O by solvatochromic shift methods.

    PubMed

    Sıdır, İsa; Gülseven Sıdır, Yadigar

    2015-01-25

    Absorption and fluorescence spectra of Oil Red O (abbreviated as ORO) are recorded in various solvents with different polarity in the range of 250-900 nm, at room temperature. The solvatochromic shift methods have been used to determine the ground state (μg) and excited state (μe) dipole moments depending on dielectric constant and refractive index functions. It is observed that fluorescence spectra show positive solvatochromism whereas absorption spectra do not indicates sensitive behavior to solvent polarity. Excited state dipole moment is found as higher than those of ground state for all of the used methods and it is attributed to more polar excited state of ORO. Theoretical μg has been determined by quantum chemical calculations using DFT and semi empirical methods. HOMO, LUMO, molecular electrostatic potential (MEP) and solvent accessible surface of ORO are calculated by using DFT-B3LYP method.

  20. Unbound excited states of the N =16 closed shell nucleus 24O

    NASA Astrophysics Data System (ADS)

    Rogers, W. F.; Garrett, S.; Grovom, A.; Anthony, R. E.; Aulie, A.; Barker, A.; Baumann, T.; Brett, J. J.; Brown, J.; Christian, G.; DeYoung, P. A.; Finck, J. E.; Frank, N.; Hamann, A.; Haring-Kaye, R. A.; Hinnefeld, J.; Howe, A. R.; Islam, N. T.; Jones, M. D.; Kuchera, A. N.; Kwiatkowski, J.; Lunderberg, E. M.; Luther, B.; Meyer, D. A.; Mosby, S.; Palmisano, A.; Parkhurst, R.; Peters, A.; Smith, J.; Snyder, J.; Spyrou, A.; Stephenson, S. L.; Strongman, M.; Sutherland, B.; Taylor, N. E.; Thoennessen, M.

    2015-09-01

    Two low-lying neutron-unbound excited states of 24O, populated by proton-knockout reactions on 26F, have been measured using the MoNA and LISA arrays in combination with the Sweeper Magnet at the Coupled Cyclotron Facility at the NSCL using invariant mass spectroscopy. The current measurement confirms the separate identity of two states with decay energies 0.51(5) MeV and 1.20(7) MeV, and provides support for theoretical model calculations, which predict a 2+ first excited state and a 1+ higher-energy state. The measured excitation energies for these states, 4.70(15) MeV for the 2+ level and 5.39(16) MeV for the 1+ level, are consistent with previous lower-resolution measurements, and are compared with five recent model predictions.

  1. The excited spin-triplet state of a charged exciton in quantum dots.

    PubMed

    Molas, M R; Nicolet, A A L; Piętka, B; Babiński, A; Potemski, M

    2016-09-14

    We report on spectroscopic studies of resonances related to ladder of states of a charged exciton in single GaAlAs/AlAs quantum dot structures. Polarization-resolved photoluminescence, photoluminescence excitation and photon-correlation measurements were performed at low (T  =  4.2 K) temperature also in magnetic field applied in Faraday configuration. The investigated resonances are assigned to three different configurations of a positively charged exciton. Together with a singlet ground state and a conventional triplet state (involving an electron from the ground state electronic s-shell), an excited triplet state, which involved an electron from the excited electronic p-shell was identified in single dots. The appearance of an emission line related to the latter complex is due to a partially suppressed electron relaxation in the investigated dots. An analysis of this emission line allows us to scrupulously determine properties of the excited triplet state and compare them with those of the conventional triplet state. Both triplets exhibit similar patterns of anisotropic fine structure and Zeeman splitting, however their amplitudes significantly differ for those two states. Presented results emphasize the role of the symmetry of the electronic state on the properties of the triplet states of two holes  +  electron excitonic complex. PMID:27391126

  2. The excited spin-triplet state of a charged exciton in quantum dots

    NASA Astrophysics Data System (ADS)

    Molas, M. R.; Nicolet, A. A. L.; Piętka, B.; Babiński, A.; Potemski, M.

    2016-09-01

    We report on spectroscopic studies of resonances related to ladder of states of a charged exciton in single GaAlAs/AlAs quantum dot structures. Polarization-resolved photoluminescence, photoluminescence excitation and photon-correlation measurements were performed at low (T  =  4.2 K) temperature also in magnetic field applied in Faraday configuration. The investigated resonances are assigned to three different configurations of a positively charged exciton. Together with a singlet ground state and a conventional triplet state (involving an electron from the ground state electronic s-shell), an excited triplet state, which involved an electron from the excited electronic p-shell was identified in single dots. The appearance of an emission line related to the latter complex is due to a partially suppressed electron relaxation in the investigated dots. An analysis of this emission line allows us to scrupulously determine properties of the excited triplet state and compare them with those of the conventional triplet state. Both triplets exhibit similar patterns of anisotropic fine structure and Zeeman splitting, however their amplitudes significantly differ for those two states. Presented results emphasize the role of the symmetry of the electronic state on the properties of the triplet states of two holes  +  electron excitonic complex.

  3. Coherent Excited States in Superconductors due to a Microwave Field.

    PubMed

    Semenov, A V; Devyatov, I A; de Visser, P J; Klapwijk, T M

    2016-07-22

    We describe theoretically the depairing effect of a microwave field on diffusive s-wave superconductors. The ground state of the superconductor is altered qualitatively in analogy to the depairing due to a dc current. In contrast to dc depairing, the density of states acquires, for microwaves with frequency ω_{0}, steps at multiples of the photon energy Δ±nℏω_{0} and shows an exponential-like tail in the subgap regime. We show that this ac depairing explains the measured frequency shift of a superconducting resonator with microwave power at low temperatures. PMID:27494495

  4. Coherent Excited States in Superconductors due to a Microwave Field

    NASA Astrophysics Data System (ADS)

    Semenov, A. V.; Devyatov, I. A.; de Visser, P. J.; Klapwijk, T. M.

    2016-07-01

    We describe theoretically the depairing effect of a microwave field on diffusive s -wave superconductors. The ground state of the superconductor is altered qualitatively in analogy to the depairing due to a dc current. In contrast to dc depairing, the density of states acquires, for microwaves with frequency ω0, steps at multiples of the photon energy Δ ±n ℏω0 and shows an exponential-like tail in the subgap regime. We show that this ac depairing explains the measured frequency shift of a superconducting resonator with microwave power at low temperatures.

  5. Ionization potential for excited S states of the lithium atom

    SciTech Connect

    Puchalski, M.; KePdziera, D.; Pachucki, K.

    2010-12-15

    Nonrelativistic, relativistic, quantum electrodynamic, and finite nuclear mass corrections to the energy levels are obtained for the nS{sub 1/2},n=3,...,9 states of the lithium atom. Computational approach is based on the explicitly correlated Hylleraas functions with the analytic integration and recursion relations. Theoretical predictions for the ionization potential of nS{sub 1/2} states and transition energies nS{sub 1/2{yields}}2S{sub 1/2} are compared to known experimental values for {sup 6,7}Li isotopes.

  6. Nonadiabatic Excited-State Molecular Dynamics Modeling of Photoinduced Dynamics in Conjugated Molecules

    SciTech Connect

    Nelson, Tammie; Fernandez-Alberti, Sebastian; Chernyak, Vladimir; Roitberg, Adrian E.; Tretiak, Sergei

    2011-01-10

    Nonadiabatic dynamics generally defines the entire evolution of electronic excitations in optically active molecular materials. It is commonly associated with a number of fundamental and complex processes such as intraband relaxation, energy transfer, and light harvesting influenced by the spatial evolution of excitations and transformation of photoexcitation energy into electrical energy via charge separation (e.g., charge injection at interfaces). To treat ultrafast excited-state dynamics and exciton/charge transport we have developed a nonadiabatic excited-state molecular dynamics (NA-ESMD) framework incorporating quantum transitions. Our calculations rely on the use of the Collective Electronic Oscillator (CEO) package accounting for many-body effects and actual potential energy surfaces of the excited states combined with Tully’s fewest switches algorithm for surface hopping for probing nonadiabatic processes. This method is applied to model the photoinduced dynamics of distyrylbenzene (a small oligomer of polyphenylene vinylene, PPV). Our analysis shows intricate details of photoinduced vibronic relaxation and identifies specific slow and fast nuclear motions that are strongly coupled to the electronic degrees of freedom, namely, torsion and bond length alternation, respectively. Nonadiabatic relaxation of the highly excited mA{sub g} state is predicted to occur on a femtosecond time scale at room temperature and on a picosecond time scale at low temperature.

  7. Nonadiabatic excited-state molecular dynamics modeling of photoinduced dynamics in conjugated molecules.

    PubMed

    Nelson, Tammie; Fernandez-Alberti, Sebastian; Chernyak, Vladimir; Roitberg, Adrian E; Tretiak, Sergei

    2011-05-12

    Nonadiabatic dynamics generally defines the entire evolution of electronic excitations in optically active molecular materials. It is commonly associated with a number of fundamental and complex processes such as intraband relaxation, energy transfer, and light harvesting influenced by the spatial evolution of excitations and transformation of photoexcitation energy into electrical energy via charge separation (e.g., charge injection at interfaces). To treat ultrafast excited-state dynamics and exciton/charge transport we have developed a nonadiabatic excited-state molecular dynamics (NA-ESMD) framework incorporating quantum transitions. Our calculations rely on the use of the Collective Electronic Oscillator (CEO) package accounting for many-body effects and actual potential energy surfaces of the excited states combined with Tully's fewest switches algorithm for surface hopping for probing nonadiabatic processes. This method is applied to model the photoinduced dynamics of distyrylbenzene (a small oligomer of polyphenylene vinylene, PPV). Our analysis shows intricate details of photoinduced vibronic relaxation and identifies specific slow and fast nuclear motions that are strongly coupled to the electronic degrees of freedom, namely, torsion and bond length alternation, respectively. Nonadiabatic relaxation of the highly excited mA(g) state is predicted to occur on a femtosecond time scale at room temperature and on a picosecond time scale at low temperature. PMID:21218841

  8. Double excitations and state-to-state transition dipoles in π-π∗ excited singlet states of linear polyenes: Time-dependent density-functional theory versus multiconfigurational methods

    NASA Astrophysics Data System (ADS)

    Mikhailov, Ivan A.; Tafur, Sergio; Masunov, Artëm E.

    2008-01-01

    The effect of static and dynamic electron correlation on the nature of excited states and state-to-state transition dipole moments is studied with a multideterminant wave function approach on the example of all-trans linear polyenes ( C4H6 , C6H8 , and C8H10 ). Symmetry-forbidden singlet nAg states were found to separate into three groups: purely single, mostly single, and mostly double excitations. The excited-state absorption spectrum is dominated by two bright transitions: 1Bu-2Ag and 1Bu-mAg , where mAg is the state, corresponding to two-electron excitation from the highest occupied to lowest unoccupied molecular orbital. The richness of the excited-state absorption spectra and strong mixing of the doubly excited determinants into lower- nAg states, reported previously at the complete active space self-consistent field level of theory, were found to be an artifact of the smaller active space, limited to π orbitals. When dynamic σ-π correlation is taken into account, single- and double-excited states become relatively well separated at least at the equilibrium geometry of the ground state. This electronic structure is closely reproduced within time-dependent density-functional theory (TD DFT), where double excitations appear in a second-order coupled electronic oscillator formalism and do not mix with the single excitations obtained within the linear response. An extension of TD DFT is proposed, where the Tamm-Dancoff approximation (TDA) is invoked after the linear response equations are solved (a posteriori TDA). The numerical performance of this extension is validated against multideterminant-wave-function and quadratic-response TD DFT results. It is recommended for use with a sum-over-states approach to predict the nonlinear optical properties of conjugated molecules.

  9. Excited State Trends in Bidirectionally Expanded Closed-Shell PAH and PANH Anions.

    PubMed

    Fortenberry, Ryan C; Moore, Megan M; Lee, Timothy J

    2016-09-22

    Some anions are known to exhibit excited states independent of external forces such as dipole moments and induced polarizabilities. Such states exist simply as a result of the stabilization of valence accepting orbitals whereby the binding energy of the extra electron is greater than the valence excitation energy. Closed-shell anions are interesting candidates for such transitions since their ground-state, spin-paired nature makes the anions more stable from the beginning. Consequently, this work shows the point beyond which deprotonated, closed-shell polycyclic aromatic hydrocarbons (PAHs) and those PAHs containing nitrogen heteroatoms (PANHs) will exhibit valence excited states. This behavior has already been demonstrated in some PANHs and for anistropically extended PAHs. This work establishes a general trend for PAHs/PANHs of arbitrary size and directional extension, whether in one dimension or two. Once seven six-membered rings make up a PAH/PANH, valence excited states are present. For most classes of PAHs/PANHs, this number is closer to four. Even though most of these excited states are weak absorbers, the sheer number of PAHs present in various astronomical environments should make them significant contributors to astronomical spectra. PMID:27585793

  10. Ultrafast excited-state charge-transfer dynamics in laccase type I copper site.

    PubMed

    Delfino, Ines; Viola, Daniele; Cerullo, Giulio; Lepore, Maria

    2015-01-01

    Femtosecond pump-probe spectroscopy was used to investigate the excited state dynamics of the T1 copper site of laccase from Pleurotus ostreatus, by exciting its 600 nm charge transfer band with a 15-fs pulse and probing over a broad range in the visible region. The decay of the pump-induced ground-state bleaching occurs in a single step and is modulated by clearly visible oscillations. Global analysis of the two-dimensional differential transmission map shows that the excited state exponentially decays with a time constant of 375 fs, thus featuring a decay rate slower than those occurring in quite all the investigated T1 copper site proteins. The ultrashort pump pulse induces a vibrational coherence in the protein, which is mainly assigned to ground state activity, as expected in a system with fast excited state decay. Vibrational features are discussed also in comparison with the traditional resonance Raman spectrum of the enzyme. The results indicate that both excited state dynamics and vibrational modes associated with the T1 Cu laccase charge transfer have main characteristics similar to those of all the T1 copper site-containing proteins. On the other hand, the differences observed for laccase from P. ostreatus further confirm the peculiar hypothesized trigonal T1 Cu site geometry. PMID:25819432

  11. How To Reach Intense Luminescence for Compounds Capable of Excited-State Intramolecular Proton Transfer?

    PubMed

    Skonieczny, Kamil; Yoo, Jaeduk; Larsen, Jillian M; Espinoza, Eli M; Barbasiewicz, Michał; Vullev, Valentine I; Lee, Chang-Hee; Gryko, Daniel T

    2016-05-23

    Photoinduced intramolecular direct arylation allows structurally unique compounds containing phenanthro[9',10':4,5]imidazo[1,2-f]phenanthridine and imidazo[1,2-f]phenanthridine skeletons, which mediate excited-state intramolecular proton transfer (ESIPT), to be efficiently synthesized. The developed polycyclic aromatics demonstrate that the combination of five-membered ring structures with a rigid arrangement between a proton donor and a proton acceptor provides a means for attaining large fluorescence quantum yields, exceeding 0.5, even in protic solvents. Steady-state and time-resolved UV/Vis spectroscopy reveals that, upon photoexcitation, the prepared protic heteroaromatics undergo ESIPT, converting them efficiently into their excited-state keto tautomers, which have lifetimes ranging from about 5 to 10 ns. The rigidity of their structures, which suppresses nonradiative decay pathways, is believed to be the underlying reason for the nanosecond lifetimes of these singlet excited states and the observed high fluorescence quantum yields. Hydrogen bonding with protic solvents does not interfere with the excited-state dynamics and, as a result, there is no difference between the occurrences of ESIPT processes in MeOH versus cyclohexane. Acidic media has a more dramatic effect on suppressing ESIPT by protonating the proton acceptor. As a result, in the presence of an acid, a larger proportion of the fluorescence of ESIPT-capable compounds originates from their enol excited states.

  12. Excited State Trends in Bidirectionally Expanded Closed-Shell PAH and PANH Anions.

    PubMed

    Fortenberry, Ryan C; Moore, Megan M; Lee, Timothy J

    2016-09-22

    Some anions are known to exhibit excited states independent of external forces such as dipole moments and induced polarizabilities. Such states exist simply as a result of the stabilization of valence accepting orbitals whereby the binding energy of the extra electron is greater than the valence excitation energy. Closed-shell anions are interesting candidates for such transitions since their ground-state, spin-paired nature makes the anions more stable from the beginning. Consequently, this work shows the point beyond which deprotonated, closed-shell polycyclic aromatic hydrocarbons (PAHs) and those PAHs containing nitrogen heteroatoms (PANHs) will exhibit valence excited states. This behavior has already been demonstrated in some PANHs and for anistropically extended PAHs. This work establishes a general trend for PAHs/PANHs of arbitrary size and directional extension, whether in one dimension or two. Once seven six-membered rings make up a PAH/PANH, valence excited states are present. For most classes of PAHs/PANHs, this number is closer to four. Even though most of these excited states are weak absorbers, the sheer number of PAHs present in various astronomical environments should make them significant contributors to astronomical spectra.

  13. Ultrafast excited-state charge-transfer dynamics in laccase type I copper site.

    PubMed

    Delfino, Ines; Viola, Daniele; Cerullo, Giulio; Lepore, Maria

    2015-01-01

    Femtosecond pump-probe spectroscopy was used to investigate the excited state dynamics of the T1 copper site of laccase from Pleurotus ostreatus, by exciting its 600 nm charge transfer band with a 15-fs pulse and probing over a broad range in the visible region. The decay of the pump-induced ground-state bleaching occurs in a single step and is modulated by clearly visible oscillations. Global analysis of the two-dimensional differential transmission map shows that the excited state exponentially decays with a time constant of 375 fs, thus featuring a decay rate slower than those occurring in quite all the investigated T1 copper site proteins. The ultrashort pump pulse induces a vibrational coherence in the protein, which is mainly assigned to ground state activity, as expected in a system with fast excited state decay. Vibrational features are discussed also in comparison with the traditional resonance Raman spectrum of the enzyme. The results indicate that both excited state dynamics and vibrational modes associated with the T1 Cu laccase charge transfer have main characteristics similar to those of all the T1 copper site-containing proteins. On the other hand, the differences observed for laccase from P. ostreatus further confirm the peculiar hypothesized trigonal T1 Cu site geometry.

  14. First-Principles Studies of the Excited States of Chromophore Monomers and Dimers

    NASA Astrophysics Data System (ADS)

    Hamed, Samia; Sharifzadeh, Sahar; Neaton, Jeffrey

    2015-03-01

    Elucidation of the energy transfer mechanism in natural photosynthetic systems remains an exciting challenge. Through the careful analysis of excited states on individual chromophores and dimers - and the predictive first-principles methods used to compute them - we are building towards an understanding of the nature of excitation transfer among arrays of chromophores embedded in protein environments. Excitation energies, transition dipoles, and natural transition orbitals for the important low-lying singlet and triplet states of experimentally-relevant chromophores are obtained from first-principles time-dependent density functional theory (TDDFT) and many body perturbation theory. The effect of the Tamm-Dancoff approximation and the performance of several exchange-correlation functionals, including an optimally-tuned range-separated hybrid, are evaluated with TDDFT, and compared to MBPT calculations and experiments. This work has been supported by the DOE; computational resources have been provided by NERSC.

  15. Excited doublet and quartet states of SiP: a high level theoretical investigation

    NASA Astrophysics Data System (ADS)

    dos Santos, Levi G.; Ornellas, Fernando R.

    2003-12-01

    Doublet and quartet states of the SiP molecule dissociating into the four lowest dissociation channels are characterized theoretically at a high-level of correlation treatment (multireference single and double excitation configuration interaction). Potential energy curves give a global view of the manifold of possible electronic states. For selected states, dipole and transition moment functions, and transition probabilities and radiative lifetimes are also reported as well as an extensive set of spectroscopic constants. A new 2Π state offers another likely route for exploring transitions to excited vibrational states of both X 2Π and A 2Σ+ states. A detailed set of data for the quartet states is expected to provide valuable information for the experimental identification of these states.

  16. Nonequilibrium solvent effects in Born-Oppenheimer molecular dynamics for ground and excited electronic states.

    PubMed

    Bjorgaard, J A; Velizhanin, K A; Tretiak, S

    2016-04-21

    The effects of solvent on molecular processes such as excited state relaxation and photochemical reaction often occurs in a nonequilibrium regime. Dynamic processes such as these can be simulated using excited statemolecular dynamics. In this work, we describe methods of simulating nonequilibrium solvent effects in excited statemolecular dynamics using linear-response time-dependent density functional theory and apparent surface charge methods. These developments include a propagation method for solvent degrees of freedom and analytical energy gradients for the calculation of forces. Molecular dynamics of acetaldehyde in water or acetonitrile are demonstrated where the solute-solvent system is out of equilibrium due to photoexcitation and emission. PMID:27389206

  17. Total electron scattering and electronic state excitations cross sections for O2, CO, and CH4

    NASA Technical Reports Server (NTRS)

    Kanik, I.; Trajmar, S.; Nickel, J. C.

    1993-01-01

    Available electron collision cross section data concerning total and elastic scattering, vibrational excitation, and ionization for O2, CO, and CH4 have been critically reviewed, and a set of cross sections for modeling of planetary atmospheric behavior is recommended. Utilizing these recommended cross sections, we derived total electronic state excitation cross sections and upper limits for dissociation cross sections, which in the case of CH4 should very closely equal the actual dissociation cross section.

  18. Discrimination of nuclear spin isomers exploiting the excited state dynamics of a quinodimethane derivative

    SciTech Connect

    Obaid, Rana; Kinzel, Daniel; Oppel, Markus González, Leticia

    2014-10-28

    Despite the concept of nuclear spin isomers (NSIs) exists since the early days of quantum mechanics, only few approaches have been suggested to separate different NSIs. Here, a method is proposed to discriminate different NSIs of a quinodimethane derivative using its electronic excited state dynamics. After electronic excitation by a laser field with femtosecond time duration, a difference in the behavior of several quantum mechanical operators can be observed. A pump-probe experimental approach for separating these different NSIs is then proposed.

  19. Excitation energies of particle-hole states in {sup 208}Pb and the surface delta interaction

    SciTech Connect

    Heusler, A.; Jolos, R. V.; Brentano, P. von

    2013-07-15

    The schematic shell model without residual interaction (SSM) assumes the same excitation energy for all spins in each particle-hole configuration multiplet. In {sup 208}Pb, more than forty states are known to contain almost the full strength of a single particle-hole configuration. The experimental excitation energy for a state with a certain spin differs from the energy predicted by the SSM by -0.2 to +0.6 MeV. The multiplet splitting is calculated with the surface delta interaction; it corresponds to the diagonal matrix element of the residual interaction in the SSM. For states containing more than 90% strength of a certain configuration and for the centroid of several completely observed configurations, the calculated multiplet splitting often approximates the experimental excitation energy within 30 keV. The strong mixing within some pairs of states containing the full strengths of two configurations is explained.

  20. Vibronic resonances facilitate excited-state coherence in light-harvesting proteins at room temperature.

    PubMed

    Novelli, Fabio; Nazir, Ahsan; Richards, Gethin H; Roozbeh, Ashkan; Wilk, Krystyna E; Curmi, Paul M G; Davis, Jeffrey A

    2015-11-19

    Until recently it was believed that photosynthesis, a fundamental process for life on earth, could be fully understood with semiclassical models. However, puzzling quantum phenomena have been observed in several photosynthetic pigment-protein complexes, prompting questions regarding the nature and role of these effects. Recent attention has focused on discrete vibrational modes that are resonant or quasi-resonant with excitonic energy splittings and strongly coupled to these excitonic states. Here we unambiguously identify excited state coherent superpositions in photosynthetic light-harvesting complexes using a new experimental approach. Decoherence on the time scale of the excited state lifetime allows low energy (56 cm(-1)) oscillations on the signal intensity to be observed. In conjunction with an appropriate model, these oscillations provide clear and direct experimental evidence that the persistent coherences observed originate from quantum superpositions among vibronic excited states. PMID:26528956

  1. Electro-optical parameters in excited states of some spectrally active molecules

    NASA Astrophysics Data System (ADS)

    Benchea, Andreea Celia; Closca, Valentina; Rusu, Cristina Marcela; Morosanu, Cezarina; Dorohoi, Dana Ortansa

    2014-08-01

    The spectral shifts measured in different solvents are expressed as functions of the solvent macroscopic parameters. The value of the correlation coefficient multiplying the functions of electric permittivity was determined by statistical means. The correlation coefficient depends on the electric dipole moment of the spectrally active molecules. The electro-optical parameters in the ground state of the solute molecules can be approximated by molecular modeling. The excited state parameters are usually estimated using the results obtained both by HyperChem Programme and solvatochromic study. The importance of this approximate method is that it offers information about of the excited state of solute molecule for which our measuring possibilities are very restrictive. The information about the excited electronic state is affected by the limits in which the theories of liquid solutions are developed. Our results refer to two molecules of vitamins from B class, namely B3 and B6.

  2. Communication: Hartree-Fock description of excited states of H{sub 2}

    SciTech Connect

    Barca, Giuseppe M. J.; Gilbert, Andrew T. B.; Gill, Peter M. W.

    2014-09-21

    Hartree-Fock (HF) theory is most often applied to study the electronic ground states of molecular systems. However, with the advent of numerical techniques for locating higher solutions of the self-consistent field equations, it is now possible to examine the extent to which such mean-field solutions are useful approximations to electronic excited states. In this Communication, we use the maximum overlap method to locate 11 low-energy solutions of the HF equation for the H{sub 2} molecule and we find that, with only one exception, these yield surprisingly accurate models for the low-lying excited states of this molecule. This finding suggests that the HF solutions could be useful first-order approximations for correlated excited state wavefunctions.

  3. A comparison of excited state properties between two different N-heterocyclic platinum(II) complexes

    NASA Astrophysics Data System (ADS)

    Yang, Baozhu; Huang, Shuang; Zhong, Jing; Zhang, Hongxing

    2015-10-01

    A comparison of excited state and electroluminescent properties between Pt(C^N^N)Cl and Pt(N^C^N)Cl complexes has been done with Time-Dependent Density Functional Theory (TDDFT), [C^N^N = 6-phenyl-2,2-bipyridine, N^C^N = 1,3-di(2-pyridyl)benzene]. The substituent effect of fluorine ligands on eight tridentate cyclometalated Pt(C^N^N)Cl complexes has been investigated, which includes electronic density variation between ground states and excited states, absorption and emission spectra, quantum yields and radiative lifetime. In addition, one dimeric form of Pt(C^N^N)Cl complex has been investigated.

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

    SciTech Connect

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

    2010-06-01

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

  5. Signature of triply excited Li-like V states in ion-solid collisions

    NASA Astrophysics Data System (ADS)

    Sharma, Gaurav; Haris, K.; Singh, G.; Kumar, B.; Karmakar, S.; Puri, N. K.; Mishra, Adya P.; Kumar, Pravin; Nandi, T.

    2016-10-01

    The transitions originating from triply excited, doubly autoionizing states of Li-like V formed in beam-foil experiments detected within a set of blended spectroscopic profiles have been assigned tentatively by the Hartree-Fock calculations including relativistic corrections and multi-configuration interactions as perturbations. The x-ray decay channels from the triply excited states such as 3p34S, 2p2 np4S (n ∼ 12) through radiative transitions to the ground state via two or more steps have been observed.

  6. Strong excited state absorption (ESA) in Yb-doped fiber lasers

    NASA Astrophysics Data System (ADS)

    Engholm, Magnus; Rydberg, Sara; Hammarling, Krister

    2013-03-01

    Excited state absorption (ESA) measurements performed on Yb-doped silica bers show the onset of a strong absorption band in the visible range. In this work, we perform experiments to investigate the possibility for ESA to be part of the induced optical losses (photodarkening) observed in Yb-doped ber lasers. Our results indicate that an ESA process, from the 2F5/2 excited state manifold in the Yb3+ ion to the charge-transfer state with absorption bands in the UV range, may constitute a transfer route for pump- and laser photons in the near-infrared range.

  7. Ratiometric fluorescent/colorimetric cyanide-selective sensor based on excited-state intramolecular charge transfer-excited-state intramolecular proton transfer switching.

    PubMed

    Lin, Wei-Chi; Fang, Sin-Kai; Hu, Jiun-Wei; Tsai, Hsing-Yang; Chen, Kew-Yu

    2014-05-20

    A novel salicylideneaniline-based fluorescent sensor, SB1, with a unique excited-state intramolecular charge transfer-excited-state intramolecular proton transfer (ESICT-ESIPT) coupled system was synthesized and demonstrated to fluorescently sense CN(-) with specific selectivity and high sensitivity in aqueous media based on ESICT-ESIPT switching. A large blue shift (96 nm) was also observed in the absorption spectra in response to CN(-). The bleaching of the color could be clearly observed by the naked eye. Moreover, SB1-based test strips were easily fabricated and low-cost, and could be used in practical and efficient CN(-) test kits. Density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations further support the cyanide-induced ESICT-ESIPT switching mechanism. The results provide the proof of concept that the colorimetric and ratiometric fluorescent cyanide-selective chemodosimeter can be created based on an ESICT-ESIPT coupled system. PMID:24809868

  8. Excited state structural dynamics in higher lying electronic states: S2 state of malachite green

    NASA Astrophysics Data System (ADS)

    Laptenok, Sergey P.; Addison, Kiri; Heisler, Ismael A.; Meech, Stephen R.

    2014-06-01

    The S2 fluorescence of malachite green is measured with sub 100 fs time resolution. Ultrafast spectral dynamics in the S2 state preceding S2 decay are resolved. Measurements in different solvents show that these sub 100 fs dynamics are insensitive to medium polarity and viscosity. They are thus assigned to ultrafast structural evolution between the S2 Franck-Condon and equilibrium configurations.

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

    SciTech Connect

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

    2014-01-21

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

  10. Determination of state-to-state electron-impact rate coefficients between Ar excited states: a review of combined diagnostic experiments in afterglow plasmas

    NASA Astrophysics Data System (ADS)

    Zhu, Xi-Ming; Cheng, Zhi-Wen; Carbone, Emile; Pu, Yi-Kang; Czarnetzki, Uwe

    2016-08-01

    Electron-impact excitation processes play an important role in low-temperature plasma physics. Cross section and rate coefficient data for electron-impact processes from the ground state to excited states or between two excited states are required for both diagnostics and modeling works. However, the collisional processes between excited states are much less investigated than the ones involving the ground state due to various experimental challenges. Recently, a method for determining electron excitation rate coefficients between Ar excited states in afterglow plasmas was successfully implemented and further developed to obtain large sets of collisional data. This method combines diagnostics for electron temperature, electron density, and excited species densities and kinetic modeling of excited species, from which the electron excitation rate coefficients from one of the 1s states to the other 1s states or to one of 2p or 3p states are determined (states are in Paschen’s notation). This paper reviews the above method—namely the combined diagnostics and modeling in afterglow plasmas. The results from other important approaches, including electron-beam measurement of cross sections, laser pump-probe technique for measuring rate coefficients, and theoretical calculations by R-matrix and distorted-wave models are also discussed. From a comparative study of these results, a fitted mathematical expression of excitation rate coefficients is obtained for the electron temperature range of 1-5 eV, which can be used for the collisional-radiative modeling of low-temperature Ar plasmas. At last, we report the limitations in the present dataset and give some suggestions for future work in this area.

  11. Determination of state-to-state electron-impact rate coefficients between Ar excited states: a review of combined diagnostic experiments in afterglow plasmas

    NASA Astrophysics Data System (ADS)

    Zhu, Xi-Ming; Cheng, Zhi-Wen; Carbone, Emile; Pu, Yi-Kang; Czarnetzki, Uwe

    2016-08-01

    Electron-impact excitation processes play an important role in low-temperature plasma physics. Cross section and rate coefficient data for electron-impact processes from the ground state to excited states or between two excited states are required for both diagnostics and modeling works. However, the collisional processes between excited states are much less investigated than the ones involving the ground state due to various experimental challenges. Recently, a method for determining electron excitation rate coefficients between Ar excited states in afterglow plasmas was successfully implemented and further developed to obtain large sets of collisional data. This method combines diagnostics for electron temperature, electron density, and excited species densities and kinetic modeling of excited species, from which the electron excitation rate coefficients from one of the 1s states to the other 1s states or to one of 2p or 3p states are determined (states are in Paschen’s notation). This paper reviews the above method—namely the combined diagnostics and modeling in afterglow plasmas. The results from other important approaches, including electron-beam measurement of cross sections, laser pump-probe technique for measuring rate coefficients, and theoretical calculations by R-matrix and distorted-wave models are also discussed. From a comparative study of these results, a fitted mathematical expression of excitation rate coefficients is obtained for the electron temperature range of 1–5 eV, which can be used for the collisional-radiative modeling of low-temperature Ar plasmas. At last, we report the limitations in the present dataset and give some suggestions for future work in this area.

  12. A theoretical analysis of the lowest excited states in HNO/NOH and HPO/POH

    NASA Astrophysics Data System (ADS)

    Luna, Alberto; Merchán, Manuela; Ross, Björn O.

    1995-07-01

    A theoretical study has been performed on the ground and two lowest excited states of the HNO/NOH and HPO/POH systems. Full geometry optimization was made for all states using the CASSCF method with dynamic correlation effects accounted for by second order perturbation theory (CASPT2). The computed vertical and adiabatic transition energies are in agreement with available experimental data.

  13. Slow relaxation of excited states in strain-induced quantum dots

    SciTech Connect

    Gfroerer, T.H.; Sturge, M.D.; Kash, K.; Yater, J.A.; Plaut, A.S.; Lin, P.S.; Florez, L.T.; Harbison, J.P.; Das, S.R.; Lebrun, L.

    1996-06-01

    We have studied photoluminescence from GaAs/Al{sub {ital x}}Ga{sub 1{minus}{ital x}}As strain-induced quantum dots in a magnetic field. These dots have high radiative efficiency and long ({approximately}ns) luminescent decay times. At low excitation intensities, corresponding to average carrier densities of less than one electron-hole pair per dot, excited-state ({open_quote}{open_quote}hot{close_quote}{close_quote}) luminescence due to slow interstate relaxation is observed. At intermediate intensities, where there are several electron-hole pairs per dot, the hot luminescence disappears, showing that the relaxation rate has increased. However, the excited-state emission reemerges at high excitation when the ground state is saturated. The interstate relaxation rate in the quantum dots under low excitation is at least two orders smaller than that of the host quantum well. The reduced rate is attributed to the discrete density of states in a quantum dot, which inhibits single-phonon emission because the excitons are spatially too large to couple to phonons with the required energy. When there are several electron-hole pairs per dot, carrier-carrier interaction accelerates relaxation. The magnetic field is used to separate the quantum dot states and allows us to probe how their relaxation depends on energy. We find that there is a strong increase in the relaxation rate when the sublevel energy exceeds about 20 meV. {copyright} {ital 1996 The American Physical Society.}

  14. Determination of differential cross sections for electron-impact excitation of electronic states of molecular oxygen

    SciTech Connect

    Campbell, L.; Green, M. A.; Brunger, M. J.; Teubner, P. J. O.; Cartwright, D. C.

    2000-02-01

    The development and initial results of a method for the determination of differential cross sections for electron scattering by molecular oxygen are described. The method has been incorporated into an existing package of computer programs which, given spectroscopic factors, dissociation energies and an energy-loss spectrum for electron-impact excitation, determine the differential cross sections for each electronic state relative to that of the elastic peak. Enhancements of the original code were made to deal with particular aspects of electron scattering from O{sub 2}, such as the overlap of vibrational levels of the ground state with transitions to excited states, and transitions to levels close to and above the dissocation energy in the Herzberg and Schumann-Runge continua. The utility of the code is specifically demonstrated for the ''6-eV states'' of O{sub 2}, where we report absolute differential cross sections for their excitation by 15-eV electrons. In addition an integral cross section, derived from the differential cross section measurements, is also reported for this excitation process and compared against available theoretical results. The present differential and integral cross sections for excitation of the ''6-eV states'' of O{sub 2} are the first to be reported in the literature for electron-impact energies below 20 eV. (c) 2000 The American Physical Society.

  15. Energy Dispersive XAFS: Characterization of Electronically Excited States of Copper(I) Complexes

    PubMed Central

    2013-01-01

    Energy dispersive X-ray absorption spectroscopy (ED-XAS), in which the whole XAS spectrum is acquired simultaneously, has been applied to reduce the real-time for acquisition of spectra of photoinduced excited states by using a germanium microstrip detector gated around one X-ray bunch of the ESRF (100 ps). Cu K-edge XAS was used to investigate the MLCT states of [Cu(dmp)2]+ (dmp =2,9-dimethyl-1,10-phenanthroline) and [Cu(dbtmp)2]+ (dbtmp =2,9-di-n-butyl-3,4,7,8-tetramethyl-1,10-phenanthroline) with the excited states created by excitation at 450 nm (10 Hz). The decay of the longer lived complex with bulky ligands, was monitored for up to 100 ns. DFT calculations of the longer lived MLCT excited state of [Cu(dbp)2]+ (dbp =2,9-di-n-butyl-1,10-phenanthroline) with the bulkier diimine ligands, indicated that the excited state behaves as a Jahn–Teller distorted Cu(II) site, with the interligand dihedral angle changing from 83 to 60° as the tetrahedral coordination geometry flattens and a reduction in the Cu–N distance of 0.03 Å. PMID:23718738

  16. Ultrafast Dynamics of 1,3-Cyclohexadiene in Highly Excited States

    DOE PAGES

    Bühler, Christine C.; Minitti, Michael P.; Deb, Sanghamitra; Bao, Jie; Weber, Peter M.

    2011-01-01

    The ultrafast dynamics of 1,3-cyclohexadiene has been investigated via structurally sensitive Rydberg electron binding energies and shown to differ upon excitation to the 1B state and the 3p Rydberg state. Excitation of the molecule with 4.63 eV photons into the ultrashort-lived 1B state yields the well-known ring opening to 1,3,5-hexatriene, while a 5.99 eV photon lifts the molecule directly into the 3p-Rydberg state. Excitation to 3p does not induce ring opening. In both experiments, time-dependent shifts of the Rydberg electron binding energy reflect the structural dynamics of the molecular core. Structural distortions associated with 3p-excitation cause a dynamical shift in the -more » and -binding energies by 10 and 26 meV/ps, respectively, whereas after excitation into 1B, more severe structural transformations along the ring-opening coordinate produce shifts at a rate of 40 to 60 meV/ps. The experiment validates photoionization-photoelectron spectroscopy via Rydberg states as a powerful technique to observe structural dynamics of polyatomic molecules.« less

  17. Control and utilization of ruthenium and rhodium metal complex excited states for photoactivated cancer therapy

    PubMed Central

    Knoll, Jessica D.; Turro, Claudia

    2015-01-01

    The use of visible light to produce highly selective and potent drugs through photodynamic therapy (PDT) holds much potential in the treatment of cancer. PDT agents can be designed to follow an O2-dependent mechanism by producing highly reactive species such as 1O2 and/or an O2 independent mechanism through processes such as excited state electron transfer, covalent binding to DNA or photoinduced drug delivery. Ru(II)-polypyridyl and Rh2(II,II) complexes represent an important class of compounds that can be tailored to exhibit desired photophysical properties and photochemical reactivity by judicious selection of the ligand set. Complexes with relatively long-lived excited states and planar, intercalating ligands localize on the DNA strand and photocleave DNA through 1O2 production or guanine oxidation by the excited state of the chromophore. Photoinduced ligand substitution occurs through the population of triplet metal centered (3MC) excited states and facilitates covalent binding of the metal complex to DNA in a mode similar to cisplatin. Ligand photodissociation also provides a route to selective drug delivery. The ability to construct metal complexes with desired light absorbing and excited state properties by ligand variation enables the design of PDT agents that can potentially provide combination therapy from a single metal complex. PMID:25729089

  18. Excited-State Proton Transfer in Resveratrol and Proposed Mechanism for Plant Resistance to Fungal Infection.

    PubMed

    Simkovitch, Ron; Huppert, Dan

    2015-09-01

    Steady-state and time-resolved fluorescence techniques were employed to study the photophysics and photochemistry of trans-resveratrol. trans-Resveratrol is found in large quantities in fungi-infected grapevine-leaf tissue and plays a direct role in the resistance to plant disease. We found that trans-resveratrol in liquid solution undergoes a trans-cis isomerization process in the excited state at a rate that depends partially on the solvent viscosity, as was found in previous studies on trans-stilbene. The hydroxyl groups of the phenol moieties in resveratrol are weak photoacids. In water and methanol solutions containing weak bases such as acetate, a proton is transferred to the base within the lifetime of the excited state. When resveratrol is adsorbed on cellulose (also a component of the plant's cell wall), the cis-trans process is slow and the lifetime of the excited state increases from several tens of picoseconds in ethanol to about 1.5 ns. Excited-state proton transfer occurs when resveratrol is adsorbed on cellulose and acetate ions are in close proximity to the phenol moieties. We propose that proton transfer from excited resveratrol to the fungus acid-sensing chemoreceptor is one of the plant's resistance mechanisms to fungal infection.

  19. Electronically Excited States of Anisotropically Extended Singly-Deprotonated PAH Anions.

    PubMed

    Theis, Mallory L; Candian, Alessandra; Tielens, Alexander G G M; Lee, Timothy J; Fortenberry, Ryan C

    2015-12-31

    Polycyclic aromatic hydrocarbons (PAHs) play a significant role in the chemistry of the interstellar medium (ISM) as well as in hydrocarbon combustion. These molecules can have high levels of diversity with the inclusion of heteroatoms and the addition or removal of hydrogens to form charged or radical species. There is an abundance of data on the cationic forms of these molecules, but there have been many fewer studies on the anionic species. The present study focuses on the anionic forms of deprotonated PAHs. It has been shown in previous work that PAHs containing nitrogen heteroatoms (PANHs) have the ability to form valence excited states giving anions electronic absorption features. This work analyzes how the isoelectronic pure PAHs behave under similar structural constructions. Singly deprotonated forms of benzene, naphthalene, anthracene, and tetracene classes are examined. None of the neutral-radicals possess dipole moments large enough to support dipole-bound excited states in their corresponding closed-shell anions. Even though the PANH anion derivatives support valence excited states for three-ringed structures, it is not until four-ringed structures of the pure PAH anion derivatives that valence excited states are exhibited. However, anisotropically extended PAHs larger than tetracene will likely exhibit valence excited states. The relative energies for the anion isomers are very small for all of the systems in this study.

  20. Determination and Comparison of Carbonyl Stretching Frequency of a Ketone in Its Ground State and the First Electronic Excited State

    ERIC Educational Resources Information Center

    Bandyopadhyay, Subhajit; Roy, Saswata

    2014-01-01

    This paper describes an inexpensive experiment to determine the carbonyl stretching frequency of an organic keto compound in its ground state and first electronic excited state. The experiment is simple to execute, clarifies some of the fundamental concepts of spectroscopy, and is appropriate for a basic spectroscopy laboratory course. The…

  1. Subpicosecond Excited-State Proton Transfer Preceding Isomerization During the Photorecovery of Photoactive Yellow Protein

    PubMed Central

    Carroll, Elizabeth C.; Song, Sang-Hun; Kumauchi, Masato; van Stokkum, Ivo H. M.; Jailaubekov, Askat; Hoff, Wouter D.; Larsen, Delmar S.

    2010-01-01

    The ultrafast excited-state dynamics underlying the receptor state photorecovery is resolved in the M100A mutant of the photoactive yellow protein (PYP) from Halorhodospira halophila. The M100A PYP mutant, with its distinctly slower photocycle than wt PYP, allows isolation of the pB signaling state for study of the photodynamics of the protonated chromophore cis-p-coumaric acid. Transient absorption signals indicate a subpicosecond excited-state proton-transfer reaction in the pB state that results in chromophore deprotonation prior to the cis–trans isomerization required in the photorecovery dynamics of the pG state. Two terminal photoproducts are observed, a blue-absorbing species presumed to be deprotonated trans-p-coumaric acid and an ultraviolet-absorbing protonated photoproduct. These two photoproducts are hypothesized to originate from an equilibrium of open and closed folded forms of the signaling state, I2 and I2’. PMID:20953237

  2. Investigations into photo-excited state dynamics in colloidal quantum dots

    NASA Astrophysics Data System (ADS)

    Singh, Gaurav

    Colloidal Quantum dots (QDs) have garnered considerable scientific and technological interest as a promising material for next generation solar cells, photo-detectors, lasers, bright light-emitting diodes (LEDs), and reliable biomarkers. However, for practical realization of these applications, it is crucial to understand the complex photo-physics of QDs that are very sensitive to surface chemistry and chemical surroundings. Depending on the excitation density, QDs can support single or multiple excitations. The first part of this talk addresses evolution of QD excited state dynamics in the regime of low excitation intensity. We use temperature-resolved time-resolved fluorescence spectroscopy to study exciton dynamics from picoseconds to microseconds and use kinetic modeling based on classical electron transfer to show the effect of surface trap states on dynamics of ground-state exciton manifold in core-shell CdSe/CdS QDs. We show that the thickness of CdS shell plays an important role in interaction of CdSe core exciton states with nanocrystal environment, and find that a thicker shell can minimize the mixing of QD exciton states with surface trap states. I will then present an investigation into the dynamics of multiply-excited states in QDs. One of the key challenges in QD spectroscopy is to reliably distinguish multi- from single-excited states that have similar lifetime components and spectroscopic signatures. I will describe the development of a novel multi-pulse fluorescence technique to selectively probe multi-excited states in ensemble QD samples and determine the nature of the multi-excited state contributing to the total fluorescence even in the limit of low fluorescent yields. We find that in our sample of CdSe/CdS core/shell QDs the multi-excited emission is dominated by emissive trion states rather than biexcitons. Next, I will discuss the application of this technique to probe exciton-plasmon coupling in layered hybrid films of QD/gold nanoparticles

  3. Multiple-photon excitation imaging with an all-solid-state laser

    NASA Astrophysics Data System (ADS)

    Wokosin, David L.; Centonze, Victoria F.; White, John G.; Hird, Steven N.; Sepsenwol, S.; Malcolm, Graeme P. A.; Maker, Gareth T.; Ferguson, Allister I.

    1996-05-01

    Two-photon excitation imaging is a recently described optical sectioning technique where fluorophore excitation is confined to--and therefore defines--the optical section being observed. This characteristic offers a significant advantage over laser-scanning confocal microscopy; the volume of fluorophore excited in the minimum necessary for imaging, thereby minimizing the destructive effects of fluorophore excitation in living tissues. In addition, a confocal pinhole is not required for optical scattering--thus further reducing the excitation needed for efficient photon collection. We have set up a two-photon excitation imaging system which uses an all-solid-state, short-pulse, long-wavelength laser as an excitation source. The source is a diode-pumped, mode-locked Nd:YLF laser operating in the infrared (1047 nm). This laser is small, has modest power requirements, and has proven reliable and stable in operation. The short laser pulses from the laser are affected by the system optical path; this has been investigated with second harmonic generation derived from a nonlinear crystal. The system has been specifically designed for the study of live biological specimens. Two cell types especially sensitive to high-energy illumination, the developing Caenorhabditis elegans embryo and the crawling sperm of the nematode, Ascaris, were used to demonstrate the dramatic increase in viability when fluorescence is generated by two-photon excitation. The system has the capability of switching between two-photon and confocal imaging modes to facilitate direct comparison of theory of these two optical sectioning techniques on the same specimen. A heavily stained zebra fish embryo was used to demonstrate the increase in sectioning depth when fluorescence is generated by infrared two- photon excitation. Two-photon excitation with the 1047 nm laser produces bright images with a variety of red emitting fluorophores, and some green emitting fluorophores, commonly used in biological

  4. Nonadiabatic excited-state molecular dynamics: treatment of electronic decoherence.

    PubMed

    Nelson, Tammie; Fernandez-Alberti, Sebastian; Roitberg, Adrian E; Tretiak, Sergei

    2013-06-14

    Within the fewest switches surface hopping (FSSH) formulation, a swarm of independent trajectories is propagated and the equations of motion for the quantum coefficients are evolved coherently along each independent nuclear trajectory. That is, the phase factors, or quantum amplitudes, are retained. At a region of strong coupling, a trajectory can branch into multiple wavepackets. Directly following a hop, the two wavepackets remain in a region of nonadiabatic coupling and continue exchanging population. After these wavepackets have sufficiently separated in phase space, they should begin to evolve independently from one another, the process known as decoherence. Decoherence is not accounted for in the standard surface hopping algorithm and leads to internal inconsistency. FSSH is designed to ensure that at any time, the fraction of classical trajectories evolving on each quantum state is equal to the average quantum probability for that state. However, in many systems this internal consistency requirement is violated. Treating decoherence is an inherent problem that can be addressed by implementing some form of decoherence correction to the standard FSSH algorithm. In this study, we have implemented two forms of the instantaneous decoherence procedure where coefficients are reinitialized following hops. We also test the energy-based decoherence correction (EDC) scheme proposed by Granucci et al. and a related version where the form of the decoherence time is taken from Truhlar's Coherent Switching with Decay of Mixing method. The sensitivity of the EDC results to changes in parameters is also evaluated. The application of these computationally inexpensive ad hoc methods is demonstrated in the simulation of nonradiative relaxation in two conjugated oligomer systems, specifically poly-phenylene vinylene and poly-phenylene ethynylene. We find that methods that have been used successfully for treating small systems do not necessarily translate to large polyatomic

  5. Brush Seals for Cryogenic Applications: Performance, Stage Effects, and Preliminary Wear Results in LN2 and LH2

    NASA Technical Reports Server (NTRS)

    Proctor, Margaret P.; Walker, James F.; Perkins, H. Douglas; Hoopes, Joan F.; Williamson, G. Scott

    1996-01-01

    Brush seals are compliant contacting seals and have significantly lower leakage than labyrinth seals in gas turbine applications. Their long life and low leakage make them candidates for use in rocket engine turbopumps. Brush seals, 50.8 mm (2 in.) in diameter with a nominal 127-micron (0.005-in.) radial interference, were tested in liquid nitrogen (LN2) and liquid hydrogen (LH2) at shaft speeds up to 35,000 and 65,000 rpm, respectively, and at pressure drops up to 1.21 MPa (175 psid) per brush. A labyrinth seal was also tested in liquid nitrogen to provide a baseline. The LN2 leakage rate of a single brush seal with an initial radial shaft interference of 127 micron (0.005 in.) measured one-half to one-third the leakage rate of a 12-tooth labyrinth seal with a radial clearance of 127 micron (0.005 in.). Two brushes spaced 7.21 micron (0.248 in.) apart leaked about one-half as much as a single brush, and two brushes tightly packed together leaked about three-fourths as much as a single brush. The maximum measured groove depth on the Inconel 718 rotor with a surface finish of 0.81 micron (32 microinch) was 25 micron (0.0010 in.) after 4.3 hr of shaft rotation in liquid nitrogen. The Haynes-25 bristles wore approximately 25 to 76 micron (0.001 to 0.003 in.) under the same conditions. Wear results in liquid hydrogen were significantly different. In liquid hydrogen the rotor did not wear, but the bristle material transferred onto the rotor and the initial 127 micron (0.005 in.) radial interference was consumed. Relatively high leakage rates were measured in liquid hydrogen. More testing is required to verify the leakage performance, to validate and calibrate analysis techniques, and to determine the wear mechanisms. Performance, staging effects, and preliminary wear results are presented.

  6. Excited states from quantum Monte Carlo in the basis of Slater determinants

    SciTech Connect

    Humeniuk, Alexander; Mitrić, Roland

    2014-11-21

    Building on the full configuration interaction quantum Monte Carlo (FCIQMC) algorithm introduced recently by Booth et al. [J. Chem. Phys. 131, 054106 (2009)] to compute the ground state of correlated many-electron systems, an extension to the computation of excited states (exFCIQMC) is presented. The Hilbert space is divided into a large part consisting of pure Slater determinants and a much smaller orthogonal part (the size of which is controlled by a cut-off threshold), from which the lowest eigenstates can be removed efficiently. In this way, the quantum Monte Carlo algorithm is restricted to the orthogonal complement of the lower excited states and projects out the next highest excited state. Starting from the ground state, higher excited states can be found one after the other. The Schrödinger equation in imaginary time is solved by the same population dynamics as in the ground state algorithm with modified probabilities and matrix elements, for which working formulae are provided. As a proof of principle, the method is applied to lithium hydride in the 3-21G basis set and to the helium dimer in the aug-cc-pVDZ basis set. It is shown to give the correct electronic structure for all bond lengths. Much more testing will be required before the applicability of this method to electron correlation problems of interesting size can be assessed.

  7. A review of candidate multilayer insulation systems for potential use on wet-launched LH2 tankage for the space exploration initiative lunar missions

    NASA Technical Reports Server (NTRS)

    Knoll, Richard H.; Stochl, Robert J.; Sanabria, Rafael

    1991-01-01

    The storage of cryogenic propellants such as liquid hydrogen (LH2) and liquid oxygen (LO2) for the future Space Exploration Initiative (SEI) will require lightweight, high performance thermal protection systems (TPS's). For the near-term lunar missions, the major weight element for most of the TPS's will be multilayer insulation (MLI) and/or the special structures/systems required to accommodate the MLI. Methods of applying MLI to LH2 tankage to avoid condensation or freezing of condensible gases such as nitrogen or oxygen while in the atmosphere are discussed. Because relatively thick layers of MLI will be required for storage times of a month or more, the transient performance from ground-hold to space-hold of the systems will become important in optimizing the TPS's for many of the missions. The ground-hold performance of several candidate systems are given as well as a qualitative assessment of the transient performance effects.

  8. Ultrafast excited state deactivation of doped porous anodic alumina membranes.

    PubMed

    Makhal, Abhinandan; Sarkar, Soumik; Pal, Samir Kumar; Yan, Hongdan; Wulferding, Dirk; Cetin, Fatih; Lemmens, Peter

    2012-08-01

    Free-standing, bi-directionally permeable and ultra-thin anodic aluminum oxide (AAO) membranes establish attractive templates (host) for the synthesis of nano-dots and rods of various materials (guest). This is due to their chemical and structural integrity and high periodicity on length scales of 5-150 nm which are often used to host photoactive nano-materials for various device applications including dye-sensitized solar cells. In the present study, AAO membranes are synthesized by using electrochemical methods and a detailed structural characterization using FEG-SEM, XRD and TGA confirms the porosity and purity of the material. Defect-mediated photoluminescence quenching of the porous AAO membrane in the presence of an electron accepting guest organic molecule (benzoquinone) is studied by means of steady-state and picosecond/femtosecond-resolved luminescence measurements. Using time-resolved luminescence transients, we have also revealed light harvesting of complexes of porous alumina impregnated with inorganic quantum dots (Maple Red) or gold nanowires. Both the Förster resonance energy transfer and the nano-surface energy transfer techniques are employed to examine the observed quenching behavior as a function of the characteristic donor-acceptor distances. The experimental results will find their relevance in light harvesting devices based on AAOs combined with other materials involving a decisive energy/charge transfer dynamics.

  9. Energy-Looping Nanoparticles: Harnessing Excited-State Absorption for Deep-Tissue Imaging.

    PubMed

    Levy, Elizabeth S; Tajon, Cheryl A; Bischof, Thomas S; Iafrati, Jillian; Fernandez-Bravo, Angel; Garfield, David J; Chamanzar, Maysamreza; Maharbiz, Michel M; Sohal, Vikaas S; Schuck, P James; Cohen, Bruce E; Chan, Emory M

    2016-09-27

    Near infrared (NIR) microscopy enables noninvasive imaging in tissue, particularly in the NIR-II spectral range (1000-1400 nm) where attenuation due to tissue scattering and absorption is minimized. Lanthanide-doped upconverting nanocrystals are promising deep-tissue imaging probes due to their photostable emission in the visible and NIR, but these materials are not efficiently excited at NIR-II wavelengths due to the dearth of lanthanide ground-state absorption transitions in this window. Here, we develop a class of lanthanide-doped imaging probes that harness an energy-looping mechanism that facilitates excitation at NIR-II wavelengths, such as 1064 nm, that are resonant with excited-state absorption transitions but not ground-state absorption. Using computational methods and combinatorial screening, we have identified Tm(3+)-doped NaYF4 nanoparticles as efficient looping systems that emit at 800 nm under continuous-wave excitation at 1064 nm. Using this benign excitation with standard confocal microscopy, energy-looping nanoparticles (ELNPs) are imaged in cultured mammalian cells and through brain tissue without autofluorescence. The 1 mm imaging depths and 2 μm feature sizes are comparable to those demonstrated by state-of-the-art multiphoton techniques, illustrating that ELNPs are a promising class of NIR probes for high-fidelity visualization in cells and tissue. PMID:27603228

  10. Mechanism for the Enhanced Excited-State Lewis Acidity of Methyl Viologen.

    PubMed

    Hohenstein, Edward G

    2016-02-17

    Aqueous solutions of methyl viologen (MV(2+)) exhibit anomalous fluorescence behavior. Although it has long fluorescence lifetimes in polar solvents such as acetonitrile, MV(2+) has a short fluorescence lifetime in water. Recent experiments by Kohler and co-workers (Henrich et al. J. Phys. Chem. B 2015, 119, 2737-2748) have implicated an excited-state acid/base reaction as the source of the nonradiative decay pathway. While many chemical species exhibit enhanced Brønsted acidity in their excited state, MV(2+) is the first example of a species with enhanced Lewis acidity. Using a complete active space configuration interaction (CASCI) approach, excited-state molecular dynamics simulations of aqueous MV(2+) are performed in order to test the hypothesis that MV(2+) acts as a Lewis photoacid and to elucidate a mechanism for this behavior. These simulations show that the Lewis acidity of MV(2+) is indeed enhanced by photoexcitation. On its S1 excited state, MV(2+) reacts with water to generate a hydronium ion approximately 1.5 ps after excitation. After the hydronium ion is produced, the corresponding hydroxide ion adds to MV(2+) to form a covalently bound photoproduct and, subsequently, evolves toward a conical intersection.

  11. Application of state-multipole Heisenberg equations to Raman excitation dynamics

    SciTech Connect

    Shore, B.W.; Sacks, R.; Dixit, S.N.

    1987-09-10

    Description of detailed temporal excitation dyanmics for coherent excitation, such as is produced by idealized laser radiation, contrasts with evaluation of rate coefficients by means of generalized Golden Rule procedures; it requires an appropriate time-dependent Schroedinger equation. When the atom undergoing excitation is also affected by incoherent processes, such as collisions, this equation no longer suffices. The Heisenberg equations, or equivalent density-matrix equations, permit treatment in which coherence and incoherence play comparable roles in the excitation dynamics. Unlike rate equations, such equations must incorporate complexities that originate in the orientation degeneracy expressed by magnetic quantum numbers. In simple cases of coherent excitation, both for single-photon and multiphoton excitation, the sublevels merely require an average of 2J+1 independent Schroedinger equations. Relaxation couples the independent equations. It has been known for some time that appropriate state-multipole operators can simplify the description of many phenomena connected with optical pumping. This memo discusses application of these multipole operators to the description of Raman (or more general multiphoton) coherent excitation. In some simple limiting cases the equations simplify, but in general one has a hierarchy of coupled multipole polarizations and coherences in place of the populations and coherences that occur as variables in nondegenerate systems. 28 refs., 4 figs.

  12. Precision Excited State Lifetime Measurements for Atomic Parity Violation and Atomic Clocks

    NASA Astrophysics Data System (ADS)

    Sell, Jerry; Patterson, Brian; Gearba, Alina; Snell, Jeremy; Knize, Randy

    2016-05-01

    Measurements of excited state atomic lifetimes provide a valuable test of atomic theory, allowing comparisons between experimental and theoretical transition dipole matrix elements. Such tests are important in Rb and Cs, where atomic parity violating experiments have been performed or proposed, and where atomic structure calculations are required to properly interpret the parity violating effect. In optical lattice clocks, precision lifetime measurements can aid in reducing the uncertainty of frequency shifts due to the surrounding blackbody radiation field. We will present our technique for precisely measuring excited state lifetimes which employs mode-locked ultrafast lasers interacting with two counter-propagating atomic beams. This method allows the timing in the experiment to be based on the inherent timing stability of mode-locked lasers, while counter-propagating atomic beams provides cancellation of systematic errors due to atomic motion to first order. Our current progress measuring Rb excited state lifetimes will be presented along with future planned measurements in Yb.

  13. Di-lepton yield from the decay of excited 28Si states

    NASA Astrophysics Data System (ADS)

    Bacelar, J. C.; Buda, A.; Bałanda, A.; Krasznahorkay, A.; van der Ploeg, H.; Sujkowski, Z.; van der Woude, A.

    1994-03-01

    The first dilepton yield measurements from excited nuclear states obtained with a new Positron-Electron Pair Spectroscopic Instrument (PEPSI) are reported. Nuclear states in 28Si, with an initial excitation energy E∗ = 50 MeV, were populated via the isospin T = 0 reaction 4He + 24Mg and the mixed-isospin 3He + 25Mg reaction. In both reactions the dilepton (e +e -) and photon decay yields were measured concurrently. An excess of counts in the e +e - spectrum, over the converted photon yield, is observed in the energy region above 15 MeV. An analyses is discussed whereby the observed excess counts are assumed to represent the isoscalar E0 strength in excited nuclear states.

  14. Organic nanophotonic materials: the relationship between excited-state processes and photonic performances.

    PubMed

    Zhang, Wei; Zhao, Yong Sheng

    2016-07-12

    Nanophotonics have recently captured broad attention because of their great potential in information processing and communication, which may allow rates and bandwidth beyond what is feasible in the realm of electronics. Organic materials could be well suitable for such applications due to their ability to generate, transmit, modulate and detect light in their lightweight and flexible nanoarchitectures. Their distinct nanophotonic properties strongly depend on their extrinsic morphologies and intrinsic molecular excited-state processes. In this feature article, we mainly focus on a comprehensive understanding of the relationship between molecular excited-state processes and the advanced photonic functionalities of organic micro/nano-crystals in recent organic nanophotonic research, and then expect to provide enlightenment for the design and development of tiny photonic devices with broadband tunable properties by tailoring the excited-state processes of organic microcrystals.

  15. Organic nanophotonic materials: the relationship between excited-state processes and photonic performances.

    PubMed

    Zhang, Wei; Zhao, Yong Sheng

    2016-07-12

    Nanophotonics have recently captured broad attention because of their great potential in information processing and communication, which may allow rates and bandwidth beyond what is feasible in the realm of electronics. Organic materials could be well suitable for such applications due to their ability to generate, transmit, modulate and detect light in their lightweight and flexible nanoarchitectures. Their distinct nanophotonic properties strongly depend on their extrinsic morphologies and intrinsic molecular excited-state processes. In this feature article, we mainly focus on a comprehensive understanding of the relationship between molecular excited-state processes and the advanced photonic functionalities of organic micro/nano-crystals in recent organic nanophotonic research, and then expect to provide enlightenment for the design and development of tiny photonic devices with broadband tunable properties by tailoring the excited-state processes of organic microcrystals. PMID:26883812

  16. Electron energy-loss spectroscopy of excited states of the pyridine molecules

    NASA Astrophysics Data System (ADS)

    Linert, Ireneusz; Zubek, Mariusz

    2016-04-01

    Electron energy-loss spectra of the pyridine, C5H5N, molecules in the gas phase have been measured to investigate electronic excitation in the energy range 3.5-10 eV. The applied wide range of residual electron energy and the scattering angle range from 10° to 180° enabled to differentiate between optically-allowed and -forbidden transitions. These measurements have allowed vertical excitation energies of the triplet excited states of pyridine to be determined and tentative assignments of these states to be proposed. Some of these states have not been identified in the previous works. Contribution to the Topical Issue "Advances in Positron and Electron Scattering", edited by Paulo Limao-Vieira, Gustavo Garcia, E. Krishnakumar, James Sullivan, Hajime Tanuma and Zoran Petrovic.

  17. Electron-impact ionization cross sections out of the ground and excited states of cesium

    SciTech Connect

    Lukomski, M.; Sutton, S.; Kedzierski, W.; Reddish, T. J.; Bartschat, K.; Bartlett, P. L.; Bray, I.; Stelbovics, A. T.; McConkey, J. W.

    2006-09-15

    An atom trapping technique for determining absolute, total ionization cross sections (TICS) out of an excited atom is presented. The unique feature of our method is in utilizing Doppler cooling of neutral atoms to determine ionization cross sections. This fluorescence-monitoring experiment, which is a variant of the 'trap loss' technique, has enabled us to obtain the experimental electron impact ionization cross sections out of the Cs state between 7 eV and 400 eV. CCC, RMPS, and Born theoretical results are also presented for both the ground and excited states of cesium and rubidium. In the low energy region (<11 eV) where best agreement between these excited state measurements and theory might be expected, a discrepancy of approximately a factor of five is observed. Above this energy there are significant contributions to the TICS from both autoionization and multiple ionization.

  18. Laurdan solvatochromism: solvent dielectric relaxation and intramolecular excited-state reaction.

    PubMed Central

    Viard, M; Gallay, J; Vincent, M; Meyer, O; Robert, B; Paternostre, M

    1997-01-01

    Absorption, steady-state, and time-resolved fluorescence measurements have been performed on laurdan dissolved either in white viscous apolar solvents or in ethanol as a function of temperature. The heterogeneity of the absorption spectra in white oils or in ethanol is consistent with semiempirical calculations performed previously on Prodan. From steady-state and time-resolved fluorescence measurements in apolar media, an excited state reaction is evidenced. The bimodal lifetime distribution determined from the maximum entropy method (MEM) analysis is attributed to the radiative deexcitation of a "locally excited" (LE) state and of a "charge transfer" (CT) state, whereas a very short component (20 ps), the sign and the amplitude of which depend on the emission wavelength, is attributed to the kinetics of the interconvertion reaction. The observation of an isoemissive point in the temperature range from -50 degrees C to -110 degrees C in ethanol suggests an interconvertion between two average excited-state populations: unrelaxed and solvent-relaxed CT states. A further decrease in temperature (-190 degrees C), leading to frozen ethanol, induces an additional and important blue shift. This low temperature spectrum is partly attributed to the radiative deexcitation of the LE state. Time-resolved emission spectra (TRES) measurements at -80 degrees C in the ethanol liquid phase show a large spectral shift of approximately 2500 cm(-1) (stabilization energy of the excited state: 7.1 kcal x M(-1)). The time-dependent fluorescence shift (TDFS) is described for its major part by a nanosecond time constant. The initial part of the spectral shift reveals, however, a subnanosecond process that can be due to fast internal solvent reorientation and/or to intramolecular excited-state reactions. These two relaxation times are also detected in the analysis of the fluorescence decays in the middle range of emission energy. The activation energy of the longest process is

  19. Investigation of lightweight designs and materials for LO2 and LH2 propellant tanks for space vehicles, phase 2 and phase 3

    NASA Technical Reports Server (NTRS)

    1976-01-01

    Full size Tug LO2 and LH2 tank configurations were defined, based on selected tank geometries. These configurations were then locally modeled for computer stress analysis. A large subscale test tank, representing the selected Tug LO2 tank, was designed and analyzed. This tank was fabricated using procedures which represented production operations. An evaluation test program was outlined and a test procedure defined. The necessary test hardware was also fabricated.

  20. Vibrational modes in excited Rydberg states of acetone: A computational study

    NASA Astrophysics Data System (ADS)

    Shastri, Aparna; Singh, Param Jeet

    2016-04-01

    Computational studies of electronically excited states of the acetone molecule [(CH3)2CO] and its fully deuterated isotopologue [(CD3)2CO] are performed using the time dependent density functional (TDDFT) methodology. In addition to vertical excitation energies for singlet and triplet states, equilibrium geometries and vibrational frequencies of the n=3 Rydberg states (3s, 3p and 3d) are obtained. This is the first report of geometry optimization and frequency calculations for the 3px, 3pz, 3dyz, 3dxy, 3dxz, 3dx2-y2 and 3dz2 Rydberg states. Results of the geometry optimization indicate that the molecule retains approximate C2V geometry in most of these excited Rydberg states, with the most significant structural change seen in the CCO bond angle which is found to be reduced from the ground state value. Detailed comparison of the computationally predicted vibrational wavenumbers with experimental studies helps to confirm several of the earlier vibronic assignments while leading to revised/new assignments for some of the bands. The important role of hot bands in analysis of the room temperature photoabsorption spectra of acetone is corroborated by this study. While the vibrational frequencies in excited Rydberg states are overall found to be close to those of the ionic ground state, geometry optimization and vibrational frequency computation for each excited state proves to be very useful to arrive at a consistent set of vibronic assignments. Isotopic substitution helps in consolidating and confirming assignments. An offshoot of this study is the interpretation of the band at ~8.47 eV as the π-3s Rydberg transition converging to the second ionization potential.

  1. Measurement of excited-state lifetime using two-pulse photon echoes in rubidium vapor

    SciTech Connect

    Rotberg, E. A.; Barrett, B.; Beattie, S.; Chudasama, S.; Weel, M.; Chan, I.; Kumarakrishnan, A.

    2007-03-15

    We report a measurement of the 5P{sub 3/2} excited-state lifetime using two-pulse photon echoes in Rb vapor. The measurement is precise to {approx}1% and agrees with the best measurement of atomic lifetime in Rb. The results suggest that a measurement precise to {approx}0.25% is possible through additional data acquisition and study of systematic effects. The experiment relies on short optical pulses generated from a cw laser using acousto-optic modulators. The excitation pulses are on resonance with the F=3{yields}F{sup '}=4 transition in {sup 85}Rb or the F=2{yields}F{sup '}=3 transition in {sup 87}Rb. The resulting photon echo signal is detected using a heterodyne detection technique. The excited-state lifetime is determined by measuring the exponential decay of the echo intensity as a function of the time between the excitation pulses. We also present a study of the echo intensity as a function of excitation pulse area and compare the results to simulations based on optical Bloch equations. The simulations include the effects of spontaneous emission as well as spatial and temporal variations of the intensities of excitation pulses.

  2. Describing excited state relaxation and localization in TiO2 nanoparticles using TD-DFT

    DOE PAGES

    Berardo, Enrico; Hu, Han -Shi; van Dam, Hubertus J. J.; Shevlin, Stephen A.; Woodley, Scott M.; Kowalski, Karol; Zwijnenburg, Martijn A.

    2014-02-26

    We have investigated the description of excited state relaxation in naked and hydrated TiO2 nanoparticles using Time-Dependent Density Functional Theory (TD-DFT) with three common hybrid exchange-correlation (XC) potentials; B3LYP, CAM-B3LYP and BHLYP. Use of TD-CAM-B3LYP and TD-BHLYP yields qualitatively similar results for all structures, which are also consistent with predictions of coupled cluster theory for small particles. TD-B3LYP, in contrast, is found to make rather different predictions; including apparent conical intersections for certain particles that are not observed with TD-CAM-B3LYP nor with TD-BHLYP. In line with our previous observations for vertical excitations, the issue with TD-B3LYP appears to be themore » inherent tendency of TD-B3LYP, and other XC potentials with no or a low percentage of Hartree-Fock Like Exchange, to spuriously stabilize the energy of charge-transfer (CT) states. Even in the case of hydrated particles, for which vertical excitations are generally well described with all XC potentials, the use of TD-B3LYP appears to result in CT-problems for certain particles. We hypothesize that the spurious stabilization of CT-states by TD-B3LYP even may drive the excited state optimizations to different excited state geometries than those obtained using TD-CAM-B3LYP or TD-BHLYP. In conclusion, focusing on the TD-CAM-B3LYP and TD-BHLYP results, excited state relaxation in naked and hydrated TiO2 nanoparticles is predicted to be associated with a large Stokes’ shift.« less

  3. General active space commutator-based coupled cluster theory of general excitation rank for electronically excited states: Implementation and application to ScH

    SciTech Connect

    Hubert, Mickaël; Loras, Jessica; Fleig, Timo; Olsen, Jeppe

    2013-11-21

    We present a new implementation of general excitation rank coupled cluster theory for electronically excited states based on the single-reference multi-reference formalism. The method may include active-space selected and/or general higher excitations by means of the general active space concept. It may employ molecular integrals over the four-component Lévy-Leblond Hamiltonian or the relativistic spin-orbit-free four-component Hamiltonian of Dyall. In an initial application to ground- and excited states of the scandium monohydride molecule we report spectroscopic constants using basis sets of up to quadruple-zeta quality and up to full iterative triple excitations in the cluster operators. Effects due to spin-orbit interaction are evaluated using two-component multi-reference configuration interaction for assessing the accuracy of the coupled cluster results.

  4. Characterization of the excited states of DNA building blocks: a coupled cluster computational study.

    PubMed

    Benda, Zsuzsanna; Szalay, Péter G

    2016-09-14

    DNA building blocks consisting of up to four nucleobases are investigated using the EOM-CCSD and CC2-LR methods in two B-DNA-like arrangements of a poly-adenine:poly-thymine (poly-A:poly-T) system. Excitation energies and oscillator strengths are presented and the characteristics of the excited states are discussed. Excited states of single-stranded poly-A systems are highly delocalized, especially the spectroscopically bright states, where delocalization over up to four fragments can be observed. In the case of poly-T systems, the states are somewhat less delocalized, extending to maximally about three fragments. A single A:T Watson-Crick pair has highly localized states, while delocalization over base pairs can be observed for some excited states of the (A)2:(T)2 system, but intrastrand delocalization is more pronounced in this case, as well. As for the characteristics of the simulated UV absorption spectra, a significant decrease of intensity can be observed in the case of single strands with increasing chain length; this is due to the stacking interactions and is in accordance with previous results. On the other hand, the breaking of H-bonds between the two strands does not alter the spectral intensity considerably, it only causes a redshift of the absorption band, thus it is unable to explain the experimentally observed DNA hyperchromism on its own, and stacking interactions need to be considered for the description of this effect as well. PMID:27506397

  5. Vertical and adiabatic excitations in anthracene from quantum Monte Carlo: Constrained energy minimization for structural and electronic excited-state properties in the JAGP ansatz

    NASA Astrophysics Data System (ADS)

    Dupuy, Nicolas; Bouaouli, Samira; Mauri, Francesco; Sorella, Sandro; Casula, Michele

    2015-06-01

    We study the ionization energy, electron affinity, and the π → π∗ (1La) excitation energy of the anthracene molecule, by means of variational quantum Monte Carlo (QMC) methods based on a Jastrow correlated antisymmetrized geminal power (JAGP) wave function, developed on molecular orbitals (MOs). The MO-based JAGP ansatz allows one to rigorously treat electron transitions, such as the HOMO → LUMO one, which underlies the 1La excited state. We present a QMC optimization scheme able to preserve the rank of the antisymmetrized geminal power matrix, thanks to a constrained minimization with projectors built upon symmetry selected MOs. We show that this approach leads to stable energy minimization and geometry relaxation of both ground and excited states, performed consistently within the correlated QMC framework. Geometry optimization of excited states is needed to make a reliable and direct comparison with experimental adiabatic excitation energies. This is particularly important in π-conjugated and polycyclic aromatic hydrocarbons, where there is a strong interplay between low-lying energy excitations and structural modifications, playing a functional role in many photochemical processes. Anthracene is an ideal benchmark to test these effects. Its geometry relaxation energies upon electron excitation are of up to 0.3 eV in the neutral 1La excited state, while they are of the order of 0.1 eV in electron addition and removal processes. Significant modifications of the ground state bond length alternation are revealed in the QMC excited state geometry optimizations. Our QMC study yields benchmark results for both geometries and energies, with values below chemical accuracy if compared to experiments, once zero point energy effects are taken into account.

  6. Vertical and adiabatic excitations in anthracene from quantum Monte Carlo: Constrained energy minimization for structural and electronic excited-state properties in the JAGP ansatz

    SciTech Connect

    Dupuy, Nicolas; Bouaouli, Samira; Mauri, Francesco Casula, Michele; Sorella, Sandro

    2015-06-07

    We study the ionization energy, electron affinity, and the π → π{sup ∗} ({sup 1}L{sub a}) excitation energy of the anthracene molecule, by means of variational quantum Monte Carlo (QMC) methods based on a Jastrow correlated antisymmetrized geminal power (JAGP) wave function, developed on molecular orbitals (MOs). The MO-based JAGP ansatz allows one to rigorously treat electron transitions, such as the HOMO → LUMO one, which underlies the {sup 1}L{sub a} excited state. We present a QMC optimization scheme able to preserve the rank of the antisymmetrized geminal power matrix, thanks to a constrained minimization with projectors built upon symmetry selected MOs. We show that this approach leads to stable energy minimization and geometry relaxation of both ground and excited states, performed consistently within the correlated QMC framework. Geometry optimization of excited states is needed to make a reliable and direct comparison with experimental adiabatic excitation energies. This is particularly important in π-conjugated and polycyclic aromatic hydrocarbons, where there is a strong interplay between low-lying energy excitations and structural modifications, playing a functional role in many photochemical processes. Anthracene is an ideal benchmark to test these effects. Its geometry relaxation energies upon electron excitation are of up to 0.3 eV in the neutral {sup 1}L{sub a} excited state, while they are of the order of 0.1 eV in electron addition and removal processes. Significant modifications of the ground state bond length alternation are revealed in the QMC excited state geometry optimizations. Our QMC study yields benchmark results for both geometries and energies, with values below chemical accuracy if compared to experiments, once zero point energy effects are taken into account.

  7. Nonadiabatic excited-state molecular dynamics: modeling photophysics in organic conjugated materials.

    PubMed

    Nelson, Tammie; Fernandez-Alberti, Sebastian; Roitberg, Adrian E; Tretiak, Sergei

    2014-04-15

    To design functional photoactive materials for a variety of technological applications, researchers need to understand their electronic properties in detail and have ways to control their photoinduced pathways. When excited by photons of light, organic conjugated materials (OCMs) show dynamics that are often characterized by large nonadiabatic (NA) couplings between multiple excited states through a breakdown of the Born-Oppenheimer (BO) approximation. Following photoexcitation, various nonradiative intraband relaxation pathways can lead to a number of complex processes. Therefore, computational simulation of nonadiabatic molecular dynamics is an indispensable tool for understanding complex photoinduced processes such as internal conversion, energy transfer, charge separation, and spatial localization of excitons. Over the years, we have developed a nonadiabatic excited-state molecular dynamics (NA-ESMD) framework that efficiently and accurately describes photoinduced phenomena in extended conjugated molecular systems. We use the fewest-switches surface hopping (FSSH) algorithm to treat quantum transitions among multiple adiabatic excited state potential energy surfaces (PESs). Extended molecular systems often contain hundreds of atoms and involve large densities of excited states that participate in the photoinduced dynamics. We can achieve an accurate description of the multiple excited states using the configuration interaction single (CIS) formalism with a semiempirical model Hamiltonian. Analytical techniques allow the trajectory to be propagated "on the fly" using the complete set of NA coupling terms and remove computational bottlenecks in the evaluation of excited-state gradients and NA couplings. Furthermore, the use of state-specific gradients for propagation of nuclei on the native excited-state PES eliminates the need for simplifications such as the classical path approximation (CPA), which only uses ground-state gradients. Thus, the NA-ESMD methodology

  8. New Theoretical Developments in Exploring Electronically Excited States: Including Localized Configuration Interaction Singles and Application to Large Helium Clusters

    NASA Astrophysics Data System (ADS)

    Closser, Kristina Danielle

    This thesis presents new developments in excited state electronic structure theory. Contrasted with the ground state, the electronically excited states of atoms and molecules often are unstable and have short lifetimes, exhibit a greater diversity of character and are generally less well understood. The very unusual excited states of helium clusters motivated much of this work. These clusters consist of large numbers of atoms (experimentally 103--109 atoms) and bands of nearly degenerate excited states. For an isolated atom the lowest energy excitation energies are from 1s → 2s and 1s → 2 p transitions, and in clusters describing the lowest energy band minimally requires four states per atom. In the ground state the clusters are weakly bound by van der Waals interactions, however in the excited state they can form well-defined covalent bonds. The computational cost of quantum chemical calculations rapidly becomes prohibitive as the size of the systems increase. Standard excited-state methods such as configuration interaction singles (CIS) and time-dependent density functional theory (TD-DFT) can be used with ≈100 atoms, and are optimized to treat only a few states. Thus, one of our primary aims is to develop a method which can treat these large systems with large numbers of nearly degenerate excited states. Additionally, excited states are generally formed far from their equilibrium structures. Vertical excitations from the ground state induce dynamics in the excited states. Thus, another focus of this work is to explore the results of these forces and the fate of the excited states. Very little was known about helium cluster excited states when this work began, thus we first investigated the excitations in small helium clusters consisting of 7 or 25 atoms using CIS. The character of these excited states was determined using attachment/detachment density analysis and we found that in the n = 2 manifold the excitations could generally be interpreted as

  9. Study of intermediates from transition metal excited-state electron-transfer reactions

    SciTech Connect

    Hoffman, M.Z.

    1992-07-31

    Conventional and fast-kinetics techniques of photochemistry, photophysics, radiation chemistry, and electrochemistry were used to study the intermediates involved in transition metal excited-state electron-transfer reactions. These intermediates were excited state of Ru(II) and Cr(III) photosensitizers, their reduced forms, and species formed in reactions of redox quenchers and electron-transfer agents. Of particular concern was the back electron-transfer reaction between the geminate pair formed in the redox quenching of the photosensitizers, and the dependence of its rate on solution medium and temperature in competition with transformation and cage escape processes. (DLC)

  10. Surface-catalyzed recombination into excited electronic, vibrational, rotational, and kinetic energy states: A review

    NASA Technical Reports Server (NTRS)

    Kofsky, I. L.; Barrett, J. L.

    1985-01-01

    Laboratory experiments in which recombined CO, CO2, D2O, OH, N2, H2, and O2 molecules desorb from surfaces in excited internal and translational states are briefly reviewed. Unequilibrated distributions predominate from the principally catalytic metal substrates so far investigated. Mean kinetic energies have been observed up to approx. 3x, and in some cases less than, wall-thermal; the velocity distributions generally vary with emission angle, with non-Lambertian particle fluxes. The excitation state populations are found to depend on surface impurities, in an as yet unexplained way.

  11. Variation after Angular Momentum Projection for the Study of Excited States Based on Antisymmetrized Molecular Dynamics

    NASA Astrophysics Data System (ADS)

    Kanada-En'yo, Y.

    1998-12-01

    In order to study the structure of excited states we perform a variational calculation after spin parity projection (VAP) within the framework of antisymmetrized molecular dynamics (AMD). The framework is proven to be a new powerful approach for the study of the various structures of excited states because it is free from model assumptions such as inert cores, existence of clusters, and the axial symmetry. By using finite range interactions with a density dependent term we reproduce well all the energy levels below 15 MeV in 12C. This is the first theoretical model that reproduces many E2 transition rates and β decays to 12C successfully.

  12. Derivative couplings between TDDFT excited states obtained by direct differentiation in the Tamm-Dancoff approximation

    NASA Astrophysics Data System (ADS)

    Ou, Qi; Fatehi, Shervin; Alguire, Ethan; Shao, Yihan; Subotnik, Joseph E.

    2014-07-01

    Working within the Tamm-Dancoff approximation, we calculate the derivative couplings between time-dependent density-functional theory excited states by assuming that the Kohn-Sham superposition of singly excited determinants represents a true electronic wavefunction. All Pulay terms are included in our derivative coupling expression. The reasonability of our approach can be established by noting that, for closely separated electronic states in the infinite basis limit, our final expression agrees exactly with the Chernyak-Mukamel expression (with transition densities from response theory). Finally, we also validate our approach empirically by analyzing the behavior of the derivative couplings around the {T}1/{T}2 conical intersection of benzaldehyde.

  13. Effects of Heavy Elements and Excited States in the Equation of State of the Solar Interior

    NASA Astrophysics Data System (ADS)

    Gong, Zhigang; Däppen, Werner; Nayfonov, Alan

    2001-12-01

    Although 98% of the solar material consists of hydrogen and helium, the remaining chemical elements contribute in a discernible way to the thermodynamic quantities. An adequate treatment of the heavy elements and their excited states is important for solar models that are subject to the stringent requirements of helioseismology. The contribution of various heavy elements in a set of thermodynamic quantities has been examined. Characteristic features that can trace individual heavy elements in the adiabatic exponent γ1=(∂lnp/∂lnϱ)s (s being specific entropy), and hence in the adiabatic sound speed, were searched. It has emerged that prominent signatures of individual elements exist and that these effects are greatest in the ionization zones, typically located near the bottom of the convection zone. The main result is that part of the features found here depend strongly on both the given species (atom or ion) and its detailed internal partition function, whereas other features only depend on the presence of the species itself, not on details such as the internal partition function. The latter features are obviously well suited for a helioseismic abundance determination, while the former features present a unique opportunity to use the Sun as a laboratory to test the validity of physical theories of partial ionization in a relatively dense and hot plasma. This domain of plasma physics has so far no competition from terrestrial laboratories. Another, quite general, finding of this work is that the inclusion of a relatively large number of heavy elements has a tendency to smear out individual features. This affects both the features that determine the abundance of elements and the ones that identify physical effects. This property alleviates the task of solar modelers because it helps to construct a good working equation of state that is relatively free of the uncertainties from basic physics. By the same token, it makes more difficult the reverse task, which is

  14. Variation of excited-state dynamics in trifluoromethyl functionalized C60 fullerenes.

    PubMed

    Park, Jaehong; Ramirez, Jessica J; Clikeman, Tyler T; Larson, Bryon W; Boltalina, Olga V; Strauss, Steven H; Rumbles, Garry

    2016-08-17

    We report on electronically excited-state dynamics of three different trifluoromethyl C60 fullerenes (TMFs, C60(CF3)n: C60/4-1, C60/6-2, and C60/10-1, featuring four, six, and ten trifluoromethyl groups, respectively) using steady-state and time-resolved optical spectroscopy as well as ultrafast pump/probe transient absorption spectroscopy. C60/4-1 and C60/6-2 dissolved in toluene solvent show near-unity S1 → T1 intersystem crossing quantum yield (ΦISC), ca. 1 ns S1-state lifetimes, and microsecond-timescale T1-state lifetimes, which are typical of the fullerene class. On the other hand, C60/10-1 exhibits a dominant sub-nanosecond nonradiative S1 → S0 relaxation mechanism and negligible ΦISC, therefore decreasing the average excited-state lifetime (τavg) by about 5 orders of magnitude compared to that of C60/4-1 and C60/6-2 (τavg ≈ 17 μs and 54 μs for C60/4-1 and C60/6-2, respectively, whereas τavg ≈ 100 ps for C60/10-1). These excited-state characteristics of C60/4-1 and C60/6-2 are preserved in polymer matrix, suggesting that fullerene/polymer interactions do not modulate intrinsic photophysics of trifluoromethyl-substituted fullerenes. The contrasting excited-state study results of C60/4-1 and C60/6-2 to that of C60/10-1 infer that intrinsic optical properties and excited-state dynamics can be affected by the substitution on the fullerene. PMID:27485768

  15. Variation of excited-state dynamics in trifluoromethyl functionalized C60 fullerenes.

    PubMed

    Park, Jaehong; Ramirez, Jessica J; Clikeman, Tyler T; Larson, Bryon W; Boltalina, Olga V; Strauss, Steven H; Rumbles, Garry

    2016-08-17

    We report on electronically excited-state dynamics of three different trifluoromethyl C60 fullerenes (TMFs, C60(CF3)n: C60/4-1, C60/6-2, and C60/10-1, featuring four, six, and ten trifluoromethyl groups, respectively) using steady-state and time-resolved optical spectroscopy as well as ultrafast pump/probe transient absorption spectroscopy. C60/4-1 and C60/6-2 dissolved in toluene solvent show near-unity S1 → T1 intersystem crossing quantum yield (ΦISC), ca. 1 ns S1-state lifetimes, and microsecond-timescale T1-state lifetimes, which are typical of the fullerene class. On the other hand, C60/10-1 exhibits a dominant sub-nanosecond nonradiative S1 → S0 relaxation mechanism and negligible ΦISC, therefore decreasing the average excited-state lifetime (τavg) by about 5 orders of magnitude compared to that of C60/4-1 and C60/6-2 (τavg ≈ 17 μs and 54 μs for C60/4-1 and C60/6-2, respectively, whereas τavg ≈ 100 ps for C60/10-1). These excited-state characteristics of C60/4-1 and C60/6-2 are preserved in polymer matrix, suggesting that fullerene/polymer interactions do not modulate intrinsic photophysics of trifluoromethyl-substituted fullerenes. The contrasting excited-state study results of C60/4-1 and C60/6-2 to that of C60/10-1 infer that intrinsic optical properties and excited-state dynamics can be affected by the substitution on the fullerene.

  16. Influence of a polarizable surrounding on the electronically excited states of aggregated perylene materials.

    PubMed

    Bellinger, Daniel; Settels, Volker; Liu, Wenlan; Fink, Reinhold F; Engels, Bernd

    2016-06-30

    To tune the efficiency of organic semiconductor devices it is important to understand limiting factors as trapping mechanisms for excitons or charges. An understanding of such mechanisms deserves an accurate description of the involved electronical states in the given environment. In this study, we investigate how a polarizable surrounding influences the relative positions of electronically excited states of dimers of different perylene dyes. Polarization effects are particularly interesting for these systems, because gas phase computations predict that the CT states lie slightly above the corresponding Frenkel states. A polarizable environment may change this energy order because CT states are thought to be more sensitive to a polarizable surrounding than Frenkel states. A first insight we got via a TD-HF approach in combination with a polarizable continuum model (PCM). These give limited insights because TD-HF overestimates excitation energies of CT states. However, SCS-CC2 approaches, which are sufficiently accurate, cannot easily be used in combination with continuum solvent models. Hence, we developed two approaches to combine gas phase SCS-CC2 results with solvent effects based on TD-HF computations. Their accuracies were finally checked via ADC(2)//COSMO computations. The results show that for perylene dyes a polarizable surrounding alone does not influence the energetic ordering of CT and Frenkel states. Variations in the energy order of the states only result from nuclear relaxation effects after the excitation process. © 2016 Wiley Periodicals, Inc. PMID:27030658

  17. Ramsey interferometry for resonant Auger decay through core-excited states

    NASA Astrophysics Data System (ADS)

    Chatterjee, Souvik; Nakajima, Takashi

    2016-08-01

    We theoretically investigate the electron dynamics in Ne atoms involving core-excited states through the Ramsey scheme with a pair of time-delayed x-ray pulses. Irradiation of Ne atoms by the ˜1 femtosecond x-ray pulse simultaneously populates two core-excited states, and an identical but time-delayed x-ray pulse probes the dynamics of the core-excited electron wave packet which is subject to the resonant Auger decay. The energy-integrated total Auger electron yield and energy-resolved Auger electron spectra in the time domain show periodic structures due to the temporal evolution of the wave packet, from which we can obtain the counterpart in the frequency domain through the Fourier transformation. The Auger electron energy spectra in the time as well as frequency domains show the interference patterns between the two Auger electron wave packets released into the continuum from the superposition of two core-excited states at different times. These spectra are important to clarify the individual contribution of the different Auger decay channels upon core excitation by the x-ray pulse.

  18. Tracking the charge and spin dynamics of electronic excited states in inorganic complexes

    NASA Astrophysics Data System (ADS)

    Gaffney, Kelly

    2015-03-01

    Inorganic complexes have many advantageous properties for solar energy applications, including strong visible absorption and photocatalytic activity. Whether used as a photocatalyst or a photosensitizer, the lifetime of electronic excited states and the earth abundance of the molecular components represent a key property for solar energy applications. These dual needs have undermined the usefulness of many coordination compounds. Isoelectronic iron and ruthenium based complexes represent a clear example. Ru-polypyridal based molecules have been the workhorse of solar energy related research and dye sensitized solar cells for decades, but the replacement of low abundance Ru with Fe leads to million-fold reductions in metal to ligand charge transfer (MLCT) excited state lifetimes. Understanding the origin of this million-fold reduction in lifetime and how to control excited state relaxation in 3d-metal complexes motivates the work I will discuss. We have used the spin sensitivity of hard x-ray fluorescence spectroscopy and the intense femtosecond duration pulses generated by the LCLS x-ray laser to probe the spin dynamics in a series of electronically excited [Fe(CN)6-2N(2,2'-bipyridine)N]2 N - 4 complexes, with N = 1-3. These femtosecond resolution measurements demonstrate that modification of the solvent and ligand environment can lengthen the MLCT excited state lifetime by more than two orders of magnitude. They also verify the role of triplet ligand field excited states in the spin crossover dynamics from singlet to quintet spin configurations. Work supported by the AMOS program within the Chemical Sciences, Geosciences, and Biosciences Division of the Office of Basic Energy Sciences, Office of Science, U.S. Department of Energy.

  19. Excited state decay of cyclometalated polypyridine ruthenium complexes: insight from theory and experiment.

    PubMed

    Kreitner, Christoph; Heinze, Katja

    2016-09-21

    Deactivation pathways of the triplet metal-to-ligand charge transfer ((3)MLCT) excited state of cyclometalated polypyridine ruthenium complexes with [RuN5C](+) coordination are discussed on the basis of the available experimental data and a series of density functional theory calculations. Three different complex classes are considered, namely with [Ru(N^N)2(N^C)](+), [Ru(N^N^N)(N^C^N)](+) and [Ru(N^N^N)(N^N^C)](+) coordination modes. Excited state deactivation in these complex types proceeds via five distinct decay channels. Vibronic coupling of the (3)MLCT state to high-energy oscillators of the singlet ground state ((1)GS) allows tunneling to the ground state followed by vibrational relaxation (path A). A ligand field excited state ((3)MC) is thermally accessible via a (3)MLCT →(3)MC transition state with the (3)MC state being strongly coupled to the (1)GS surface via a low-energy minimum energy crossing point (path B). Furthermore, a (3)MLCT →(1)GS surface crossing point directly couples the triplet and singlet potential energy surfaces (path C). Charge transfer states either with higher singlet character or with different orbital parentage and intrinsic symmetry restrictions are thermally populated which promote non-radiative decay via tunneling to the (1)GS state (path D). Finally, the excited state can decay via phosphorescence (path E). The dominant deactivation pathways differ for the three individual complex classes. The implications of these findings for isoelectronic iridium(iii) or iron(ii) complexes are discussed. Ultimately, strategies for optimizing the emission efficiencies of cyclometalated polypyridine complexes of d(6)-metal ions, especially Ru(II), are suggested. PMID:27334798

  20. Excited state decay of cyclometalated polypyridine ruthenium complexes: insight from theory and experiment.

    PubMed

    Kreitner, Christoph; Heinze, Katja

    2016-09-21

    Deactivation pathways of the triplet metal-to-ligand charge transfer ((3)MLCT) excited state of cyclometalated polypyridine ruthenium complexes with [RuN5C](+) coordination are discussed on the basis of the available experimental data and a series of density functional theory calculations. Three different complex classes are considered, namely with [Ru(N^N)2(N^C)](+), [Ru(N^N^N)(N^C^N)](+) and [Ru(N^N^N)(N^N^C)](+) coordination modes. Excited state deactivation in these complex types proceeds via five distinct decay channels. Vibronic coupling of the (3)MLCT state to high-energy oscillators of the singlet ground state ((1)GS) allows tunneling to the ground state followed by vibrational relaxation (path A). A ligand field excited state ((3)MC) is thermally accessible via a (3)MLCT →(3)MC transition state with the (3)MC state being strongly coupled to the (1)GS surface via a low-energy minimum energy crossing point (path B). Furthermore, a (3)MLCT →(1)GS surface crossing point directly couples the triplet and singlet potential energy surfaces (path C). Charge transfer states either with higher singlet character or with different orbital parentage and intrinsic symmetry restrictions are thermally populated which promote non-radiative decay via tunneling to the (1)GS state (path D). Finally, the excited state can decay via phosphorescence (path E). The dominant deactivation pathways differ for the three individual complex classes. The implications of these findings for isoelectronic iridium(iii) or iron(ii) complexes are discussed. Ultimately, strategies for optimizing the emission efficiencies of cyclometalated polypyridine complexes of d(6)-metal ions, especially Ru(II), are suggested.

  1. a Study of Quasi-One Systems: Excitation of the Active Electron to its First Excited State

    NASA Astrophysics Data System (ADS)

    Redd, Emmett Richter

    Experimental angular differential cross sections (ADCS) of four Quasi-One-Electron (QOE) scattering systems (Li('+), Na('+) + H and Be('+), Mg('+) + He) are reported. These ADCS are determined for exciting the 'active' electron to its first excited state. The angular range of the ADCS is from 0 to (TURN)3 mrad(,lab) with an angular resolution of (TURN)120 (mu)rad(,lab). The energy range is from 19.4 to 150 keV with an energy-loss resolution of (TURN)1 eV. The ADCS are compared to the available theories. The agreement between experiment and theory ranges from very poor to fair. No experiments exist which allow direct comparison to the present results. Integration of the present ADCS gives results which are compared to the experimental and theoretical total He targets cross section results. The agreement changes from energy to energy. Theoretical total cross section results exist in the cases involving H targets and are in very poor to fair agreement with the present results. No experimental total cross sections exist in the H target case for comparison with the present results. The most striking feature occurs in the Na('+) + H ADCS. Here the value of the ADCS at zero angle changes by 2 1/2 orders of magnitude from (3.96 (+OR-) 2.00) x 10('-15) cm('2)/sr at 35.9 keV (v = 1/4 a.u.) to (1.03 (+OR-) 0.25) x 10('-12) cm('2)/sr at 143.8 keV (v = 1/2 a.u.). This steep rise in the ADCS at zero angle is interpreted as showing the onset of a direct excitation mechanism (mechanism ii in the QOE literature). Qualitative agreement between previous QOE results (at lower energy using He targets) and the present Na('+) + H results is shown. Massey parameter scaling is shown to supply relatively little information on the ADCS. Finally, the results are probed to show the similarities of the underlying scattering mechanisms. For systems with the same target, the ADCS show quantitatively comparable results implying considerable similarities. Although all the systems are shown to be

  2. Double resonance spectroscopy of several highly excited rovibronic states of H2

    NASA Astrophysics Data System (ADS)

    Ekey, R. C., Jr.; McCormack, E. F.

    2005-04-01

    The energies of several highly excited levels of the B1Σ+u, B'1Σ+u and C 1Πu states of molecular hydrogen, located several hundred wave numbers below the second dissociation limit, have been measured using two-colour, resonantly enhanced multi-photon ionization. The states were probed by excitation from the double-well E, F 1Σ+u state, populated by two-photon excitation from the ground state. Ion production was detected as a function of wavelength using a time-of-flight mass spectrometer. Non-adiabatic couplings extensively mix the configurations of the B 1Σ+u, B'1Σ+u and C 1Πu states leading to perturbations that are predicted to vary considerably as a function of rotational and vibrational excitation. Term energies are compared to previous measurements and to ab initio theoretical calculations which include non-adiabatic effects. Several observed discrepancies with the calculations and previously reported energies are discussed. Term energies for two rovibronic levels are reported for the first time.

  3. A relativistic time-dependent density functional study of the excited states of the mercury dimer.

    PubMed

    Kullie, Ossama

    2014-01-14

    In previous works on Zn2 and Cd2 dimers we found that the long-range corrected CAMB3LYP gives better results than other density functional approximations for the excited states, especially in the asymptotic region. In this paper, we use it to present a time-dependent density functional (TDDFT) study for the ground-state as well as the excited states corresponding to the (6s(2) + 6s6p), (6s(2) + 6s7s), and (6s(2) + 6s7p) atomic asymptotes for the mercury dimer Hg2. We analyze its spectrum obtained from all-electron calculations performed with the relativistic Dirac-Coulomb and relativistic spinfree Hamiltonian as implemented in DIRAC-PACKAGE. A comparison with the literature is given as far as available. Our result is excellent for the most of the lower excited states and very encouraging for the higher excited states, it shows generally good agreements with experimental results and outperforms other theoretical results. This enables us to give a detailed analysis of the spectrum of the Hg2 including a comparative analysis with the lighter dimers of the group 12, Cd2, and Zn2, especially for the relativistic effects, the spin-orbit interaction, and the performance of CAMB3LYP and is enlightened for similar systems. The result shows, as expected, that spinfree Hamiltonian is less efficient than Dirac-Coulomb Hamiltonian for systems containing heavy elements such as Hg2.

  4. Renormalization of operators for excited-state hadrons in lattice QCD.

    SciTech Connect

    Ekaterina Mastropas, David Richards

    2012-04-01

    One of the primary aims of lattice QCD is to accurately compute the spectrum of hadronic excitations from first principles. However, obtaining an accurate resolution of excited states using methods of lattice QCD is not a trivial problem due to faster decay of excited-states correlation functions in Euclidean space in comparison to those of ground states. To overcome this difficulty, anisotropic lattices with a finer temporal discretization are used. To go beyond the spectrum, in order to study the properties of the states, one needs to compute corresponding matrix elements. Thus, for example, the quark distribution amplitudes in mesons are given by matrix elements of quark bilinear operators, while in baryons, the corresponding quark distribution amplitudes are related to matrix elements of three-quark operators. To relate the matrix elements calculated on the lattice to those in the continuum, and hence to relate to the measured experimentally, it is necessary to evaluate matching coefficients. In this work we describe the calculation of the matching coefficients using perturbation theory for the improved anisotropic-clover fermion action used for our studies of excited states.

  5. Carbon nanorings with inserted acenes: breaking symmetry in excited state dynamics.

    PubMed

    Franklin-Mergarejo, R; Alvarez, D Ondarse; Tretiak, S; Fernandez-Alberti, S

    2016-01-01

    Conjugated cycloparaphenylene rings have unique electronic properties being the smallest segments of carbon nanotubes. Their conjugated backbones support delocalized electronic excitations, which dynamics is strongly influenced by cyclic geometry. Here we present a comparative theoretical study of the electronic and vibrational energy relaxation and redistribution in photoexcited cycloparaphenylene carbon nanorings with inserted naphthalene, anthracene, and tetracene units using non-adiabatic excited-state molecular dynamics simulations. Calculated excited state structures reflect modifications of optical selection rules and appearance of low-energy electronic states localized on the acenes due to gradual departure from a perfect circular symmetry. After photoexcitation, an ultrafast electronic energy relaxation to the lowest excited state is observed on the time scale of hundreds of femtoseconds in all molecules studied. Concomitantly, the efficiency of the exciton trapping in the acene raises when moving from naphthalene to anthracene and to tetracene, being negligible in naphthalene, and ~60% and 70% in anthracene and tetracene within the first 500 fs after photoexcitation. Observed photoinduced dynamics is further analyzed in details using induced molecular distortions, delocatization properties of participating electronic states and non-adiabatic coupling strengths. Our results provide a number of insights into design of cyclic molecular systems for electronic and light-harvesting applications. PMID:27507429

  6. Symmetry-adapted excited states for the T1u⊗hg Jahn-Teller system

    NASA Astrophysics Data System (ADS)

    Qiu, Q. C.; Dunn, J. L.; Bates, C. A.

    2001-08-01

    Jahn-Teller (JT) systems typically contain a set of equivalent-energy wells in the lowest adiabatic potential-energy surface (APES). Quantum-mechanical tunneling between these wells (the dynamic JT effect) must be allowed for by taking appropriate symmetrized combinations of oscillator-type states associated with the wells. It is important to be able to describe the excited states of such systems for a number of reasons. One particular reason is that they are required for the calculation of second-order vibronic reduction factors, which in turn are useful for modeling experimental data using effective Hamiltonians. In this paper, projection-operator techniques are used to obtain general expressions for the symmetry-adapted excited states of the icosahedral T1u⊗hg JT system for the case of D5d minima in the APES. Analytical expressions for the states and their energies for one-phonon excitation are given explicitly. The energies of a selection of states with two-phonon excitations are also obtained and plotted. The results obtained in this paper are applicable to the C-60 molecule.

  7. Structure of low-lying states in 140Sm studied by Coulomb excitation

    NASA Astrophysics Data System (ADS)

    Klintefjord, M.; Hadyńska-KlÈ©k, K.; Görgen, A.; Bauer, C.; Bello Garrote, F. L.; Bönig, S.; Bounthong, B.; Damyanova, A.; Delaroche, J.-P.; Fedosseev, V.; Fink, D. A.; Giacoppo, F.; Girod, M.; Hoff, P.; Imai, N.; Korten, W.; Larsen, A.-C.; Libert, J.; Lutter, R.; Marsh, B. A.; Molkanov, P. L.; Naïdja, H.; Napiorkowski, P.; Nowacki, F.; Pakarinen, J.; Rapisarda, E.; Reiter, P.; Renstrøm, T.; Rothe, S.; Seliverstov, M. D.; Siebeck, B.; Siem, S.; Srebrny, J.; Stora, T.; Thöle, P.; Tornyi, T. G.; Tveten, G. M.; Van Duppen, P.; Vermeulen, M. J.; Voulot, D.; Warr, N.; Wenander, F.; De Witte, H.; Zielińska, M.

    2016-05-01

    The electromagnetic structure of 140Sm was studied in a low-energy Coulomb excitation experiment with a radioactive ion beam from the REX-ISOLDE facility at CERN. The 2+ and 4+ states of the ground-state band and a second 2+ state were populated by multistep excitation. The analysis of the differential Coulomb excitation cross sections yielded reduced transition probabilities between all observed states and the spectroscopic quadrupole moment for the 21+ state. The experimental results are compared to large-scale shell model calculations and beyond-mean-field calculations based on the Gogny D1S interaction with a five-dimensional collective Hamiltonian formalism. Simpler geometric and algebraic models are also employed to interpret the experimental data. The results indicate that 140Sm shows considerable γ softness, but in contrast to earlier speculation no signs of shape coexistence at low excitation energy. This work sheds more light on the onset of deformation and collectivity in this mass region.

  8. Carbon nanorings with inserted acenes: breaking symmetry in excited state dynamics

    NASA Astrophysics Data System (ADS)

    Franklin-Mergarejo, R.; Alvarez, D. Ondarse; Tretiak, S.; Fernandez-Alberti, S.

    2016-08-01

    Conjugated cycloparaphenylene rings have unique electronic properties being the smallest segments of carbon nanotubes. Their conjugated backbones support delocalized electronic excitations, which dynamics is strongly influenced by cyclic geometry. Here we present a comparative theoretical study of the electronic and vibrational energy relaxation and redistribution in photoexcited cycloparaphenylene carbon nanorings with inserted naphthalene, anthracene, and tetracene units using non-adiabatic excited-state molecular dynamics simulations. Calculated excited state structures reflect modifications of optical selection rules and appearance of low-energy electronic states localized on the acenes due to gradual departure from a perfect circular symmetry. After photoexcitation, an ultrafast electronic energy relaxation to the lowest excited state is observed on the time scale of hundreds of femtoseconds in all molecules studied. Concomitantly, the efficiency of the exciton trapping in the acene raises when moving from naphthalene to anthracene and to tetracene, being negligible in naphthalene, and ~60% and 70% in anthracene and tetracene within the first 500 fs after photoexcitation. Observed photoinduced dynamics is further analyzed in details using induced molecular distortions, delocatization properties of participating electronic states and non-adiabatic coupling strengths. Our results provide a number of insights into design of cyclic molecular systems for electronic and light-harvesting applications.

  9. Carbon nanorings with inserted acenes: Breaking symmetry in excited state dynamics

    DOE PAGES

    Franklin-Mergarejo, R.; Alvarez, D. Ondarse; Tretiak, S.; Fernandez-Alberti, S.

    2016-08-10

    Conjugated cycloparaphenylene rings have unique electronic properties being the smallest segments of carbon nanotubes. Their conjugated backbones support delocalized electronic excitations, which dynamics is strongly influenced by cyclic geometry. Here we present a comparative theoretical study of the electronic and vibrational energy relaxation and redistribution in photoexcited cycloparaphenylene carbon nanorings with inserted naphthalene, anthracene, and tetracene units using non-adiabatic excited-state molecular dynamics simulations. Calculated excited state structures reflect modifications of optical selection rules and appearance of low-energy electronic states localized on the acenes due to gradual departure from a perfect circular symmetry. After photoexcitation, an ultrafast electronic energy relaxation tomore » the lowest excited state is observed on the time scale of hundreds of femtoseconds in all molecules studied. Concomitantly, the efficiency of the exciton trapping in the acene raises when moving from naphthalene to anthracene and to tetracene, being negligible in naphthalene, and ~60% and 70% in anthracene and tetracene within the first 500 fs after photoexcitation. Observed photoinduced dynamics is further analyzed in details using induced molecular distortions, delocatization properties of participating electronic states and non-adiabatic coupling strengths. Lastly, our results provide a number of insights into design of cyclic molecular systems for electronic and light-harvesting applications.« less

  10. A relativistic time-dependent density functional study of the excited states of the mercury dimer

    NASA Astrophysics Data System (ADS)

    Kullie, Ossama

    2014-01-01

    In previous works on Zn2 and Cd2 dimers we found that the long-range corrected CAMB3LYP gives better results than other density functional approximations for the excited states, especially in the asymptotic region. In this paper, we use it to present a time-dependent density functional (TDDFT) study for the ground-state as well as the excited states corresponding to the (6s2 + 6s6p), (6s2 + 6s7s), and (6s2 + 6s7p) atomic asymptotes for the mercury dimer Hg2. We analyze its spectrum obtained from all-electron calculations performed with the relativistic Dirac-Coulomb and relativistic spinfree Hamiltonian as implemented in DIRAC-PACKAGE. A comparison with the literature is given as far as available. Our result is excellent for the most of the lower excited states and very encouraging for the higher excited states, it shows generally good agreements with experimental results and outperforms other theoretical results. This enables us to give a detailed analysis of the spectrum of the Hg2 including a comparative analysis with the lighter dimers of the group 12, Cd2, and Zn2, especially for the relativistic effects, the spin-orbit interaction, and the performance of CAMB3LYP and is enlightened for similar systems. The result shows, as expected, that spinfree Hamiltonian is less efficient than Dirac-Coulomb Hamiltonian for systems containing heavy elements such as Hg2.

  11. Carbon nanorings with inserted acenes: breaking symmetry in excited state dynamics

    PubMed Central

    Franklin-Mergarejo, R.; Alvarez, D. Ondarse; Tretiak, S.; Fernandez-Alberti, S.

    2016-01-01

    Conjugated cycloparaphenylene rings have unique electronic properties being the smallest segments of carbon nanotubes. Their conjugated backbones support delocalized electronic excitations, which dynamics is strongly influenced by cyclic geometry. Here we present a comparative theoretical study of the electronic and vibrational energy relaxation and redistribution in photoexcited cycloparaphenylene carbon nanorings with inserted naphthalene, anthracene, and tetracene units using non-adiabatic excited-state molecular dynamics simulations. Calculated excited state structures reflect modifications of optical selection rules and appearance of low-energy electronic states localized on the acenes due to gradual departure from a perfect circular symmetry. After photoexcitation, an ultrafast electronic energy relaxation to the lowest excited state is observed on the time scale of hundreds of femtoseconds in all molecules studied. Concomitantly, the efficiency of the exciton trapping in the acene raises when moving from naphthalene to anthracene and to tetracene, being negligible in naphthalene, and ~60% and 70% in anthracene and tetracene within the first 500 fs after photoexcitation. Observed photoinduced dynamics is further analyzed in details using induced molecular distortions, delocatization properties of participating electronic states and non-adiabatic coupling strengths. Our results provide a number of insights into design of cyclic molecular systems for electronic and light-harvesting applications. PMID:27507429

  12. Excited State Structural Dynamics of Carotenoids and ChargeTransfer Systems

    SciTech Connect

    Van Tassle, Aaron Justin

    2006-01-01

    This dissertation describes the development andimplementation of a visible/near infrared pump/mid-infrared probeapparatus. Chapter 1 describes the background and motivation ofinvestigating optically induced structural dynamics, paying specificattention to solvation and the excitation selection rules of highlysymmetric molecules such as carotenoids. Chapter 2 describes thedevelopment and construction of the experimental apparatus usedthroughout the remainder of this dissertation. Chapter 3 will discuss theinvestigation of DCM, a laser dye with a fluorescence signal resultingfrom a charge transfer state. By studying the dynamics of DCM and of itsmethyl deuterated isotopomer (an otherwise identical molecule), we areable to investigate the origins of the charge transfer state and provideevidence that it is of the controversial twisted intramolecular (TICT)type. Chapter 4 introduces the use of two-photon excitation to the S1state, combined with one-photon excitation to the S2 state of thecarotenoid beta-apo-8'-carotenal. These 2 investigations show evidencefor the formation of solitons, previously unobserved in molecular systemsand found only in conducting polymers Chapter 5 presents an investigationof the excited state dynamics of peridinin, the carotenoid responsiblefor the light harvesting of dinoflagellates. This investigation allowsfor a more detailed understanding of the importance of structuraldynamics of carotenoids in light harvesting.

  13. Vibronic structure and coupling of higher excited electronic states in carotenoids

    NASA Astrophysics Data System (ADS)

    Krawczyk, Stanisław; Luchowski, Rafał

    2013-03-01

    Absorption spectra of all-trans carotenoids (lycopene, violaxanthin, ζ-carotene) at low temperature exhibit peculiar features in the UV range. The transition to the 11Ag+ state ('cis-band') weakens on cooling, indicating that it is induced by thermal deformations of the conjugated chain. The higher energy band has unique vibrational structure indicating the vibronic coupling of nBu with another electronic state. The electroabsorption spectra point to the electric field-induced mixing of the nBu state with the vibrational continuum of a lower-lying excited state (Fano effect). These observations widen the basis for elucidation of the vibronic coupling effects in the lower excited states.

  14. An excited-state approach within full configuration interaction quantum Monte Carlo

    SciTech Connect

    Blunt, N. S.; Smart, Simon D.; Booth, George H.; Alavi, Ali

    2015-10-07

    We present a new approach to calculate excited states with the full configuration interaction quantum Monte Carlo (FCIQMC) method. The approach uses a Gram-Schmidt procedure, instantaneously applied to the stochastically evolving distributions of walkers, to orthogonalize higher energy states against lower energy ones. It can thus be used to study several of the lowest-energy states of a system within the same symmetry. This additional step is particularly simple and computationally inexpensive, requiring only a small change to the underlying FCIQMC algorithm. No trial wave functions or partitioning of the space is needed. The approach should allow excited states to be studied for systems similar to those accessible to the ground-state method due to a comparable computational cost. As a first application, we consider the carbon dimer in basis sets up to quadruple-zeta quality and compare to existing results where available.

  15. Search for excited states in {sup 7}He with the (d,p) reaction

    SciTech Connect

    Wuosmaa, A.H.; Rehm, K.E.; Greene, J.P.; Henderson, D.J.; Janssens, R.V.F.; Jiang, C.L.; Moore, E.F.; Pardo, R.C.; Peterson, D.; Pieper, Steven C.; Savard, G.; Schiffer, J.P.; Sinha, S.; Tang, X.; Wiringa, R.B.; Jisonna, L.; Segel, R.E.; Paul, M.

    2005-12-15

    We have studied the properties of low-lying levels in {sup 7}He using the {sup 2}H({sup 6}He,p){sup 7}He reaction at 11.5 MeV/u. This reaction probes the {sup 6}He{sub g.s.}+n character of states in {sup 7}He. The ground state was populated with a spectroscopic factor comparable to that obtained from ab initio calculations, supporting the tentative spin-parity assignment of 3/2{sup -} in the literature. In addition to the ground state, a broad structure is observed between E{sub X}=2-3 MeV, the excitation-energy range expected for the 1/2{sup -} state in {sup 7}He. No evidence was found for a lower-lying, first-excited state reported recently.

  16. Emergence of nontrivial magnetic excitations in a spin-liquid state of kagomé volborthite

    NASA Astrophysics Data System (ADS)

    Watanabe, Daiki; Sugii, Kaori; Shimozawa, Masaaki; Suzuki, Yoshitaka; Yajima, Takeshi; Ishikawa, Hajime; Hiroi, Zenji; Shibauchi, Takasada; Matsuda, Yuji; Yamashita, Minoru

    2016-08-01

    When quantum fluctuations destroy underlying long-range ordered states, novel quantum states emerge. Spin-liquid (SL) states of frustrated quantum antiferromagnets, in which highly correlated spins fluctuate down to very low temperatures, are prominent examples of such quantum states. SL states often exhibit exotic physical properties, but the precise nature of the elementary excitations behind such phenomena remains entirely elusive. Here, we use thermal Hall measurements that can capture the unexplored property of the elementary excitations in SL states, and report the observation of anomalous excitations that may unveil the unique features of the SL state. Our principal finding is a negative thermal Hall conductivity κxyκxy which the charge-neutral spin excitations in a gapless SL state of the 2D kagomé insulator volborthite Cu3V2O7(OH)2ṡ2H2O exhibit, in much the same way in which charged electrons show the conventional electric Hall effect. We find that κxyκxy is absent in the high-temperature paramagnetic state and develops upon entering the SL state in accordance with the growth of the short-range spin correlations, demonstrating that κxyκxy is a key signature of the elementary excitation formed in the SL state. These results suggest the emergence of nontrivial elementary excitations in the gapless SL state which feel the presence of fictitious magnetic flux, whose effective Lorentz force is found to be less than 1/100 of the force

  17. Electron-impact ionization of moderately charged atomic ions in excited states

    SciTech Connect

    Pindzola, M. S.; Ballance, C. P.; Loch, S. D.

    2011-06-15

    Nonperturbative R-matrix and perturbative distorted-wave methods are used to calculate electron-impact ionization cross sections for C{sup 3+} in excited states. Convergence studies for the cross sections of the 1s{sup 2}5s excited configuration reveal that both the R-matrix and distorted-wave methods need fairly high ejected electron angular momenta. Reasonable agreement is found between the converged R-matrix and distorted-wave cross sections. Thus, the use of the computationally less demanding distorted-wave method as a tool for the n scaling of excited-state ionization cross sections appears to be reasonable for atomic ions with charge q{>=}3.

  18. Spectroscopy and intramolecular relaxation of methyl salicylate in its first excited singlet state

    NASA Astrophysics Data System (ADS)

    Kuper, Jerry W.; Perry, David S.

    1984-05-01

    High resolution fluorescence excitation experiments are reported for the blue emitting rotamer of methyl salicylate in its first excited singlet state. These experiments employ moderate expansions of methyl salicylate seeded in argon ( P0D=5-8 Torr cm) to achieve rotational and vibrational cooling in a pulsed supersonic jet. The rotational contour of the electronic origin at 30 055.3 cm-1 is shown to be consistent with a geometrically distorted π-π* excited state, partially polarized along the A axis and with a rotational temperature of 5-7 K. A noticeable broadening of the spectral features beyond the rotational contour begins at 500 cm-1 above the origin and then increases rapidly above 900 cm-1 reaching a width of 12 cm-1 near 1200 cm-1. The constancy of fluorescence decay lifetimes in this region indicate that intramolecular vibrational relaxation in the S1 manifold is the broadening mechanism.

  19. Selective two-photon excitation of a vibronic state by correlated photons.

    PubMed

    Oka, Hisaki

    2011-03-28

    We theoretically investigate the two-photon excitation of a molecular vibronic state by correlated photons with energy anticorrelation. A Morse oscillator having three sets of vibronic states is used, as an example, to evaluate the selectivity and efficiency of two-photon excitation. We show that a vibrational mode can be selectively excited with high efficiency by the correlated photons, without phase manipulation or pulse-shaping techniques. This can be achieved by controlling the quantum correlation so that the photon pair concurrently has two pulse widths, namely, a temporally narrow width and a spectrally narrow width. Though this concurrence is seemingly contradictory, we can create such a photon pair by tailoring the quantum correlation between two photons.

  20. Electronic and Structural Elements That Regulate the Excited-State Dynamics in Purine Nucleobase Derivatives

    PubMed Central

    2015-01-01

    The excited-state dynamics of the purine free base and 9-methylpurine are investigated using experimental and theoretical methods. Femtosecond broadband transient absorption experiments reveal that excitation of these purine derivatives in aqueous solution at 266 nm results primarily in ultrafast conversion of the S2(ππ*) state to the vibrationally excited 1nπ* state. Following vibrational and conformational relaxation, the 1nπ* state acts as a doorway state in the efficient population of the triplet manifold with an intersystem crossing lifetime of hundreds of picoseconds. Experiments show an almost 2-fold increase in the intersystem crossing rate on going from polar aprotic to nonpolar solvents, suggesting that a solvent-dependent energy barrier must be surmounted to access the singlet-to-triplet crossing region. Ab initio static and surface-hopping dynamics simulations lend strong support to the proposed relaxation mechanism. Collectively, the experimental and computational results demonstrate that the accessibility of the nπ* states and the topology of the potential energy surfaces in the vicinity of conical intersections are key elements in controlling the excited-state dynamics of the purine derivatives. From a structural perspective, it is shown that the purine chromophore is not responsible for the ultrafast internal conversion in the adenine and guanine monomers. Instead, C6 functionalization plays an important role in regulating the rates of radiative and nonradiative relaxation. C6 functionalization inhibits access to the 1nπ* state while simultaneously facilitating access to the 1ππ*(La)/S0 conical intersection, such that population of the 1nπ* state cannot compete with the relaxation pathways to the ground state involving ring puckering at the C2 position. PMID:25763596

  1. Formation of metastable atomic hydrogen in the 2s state from symmetry-resolved doubly excited states of molecular hydrogen

    SciTech Connect

    Odagiri, Takeshi; Kumagai, Yoshiaki; Nakano, Motoyoshi; Tanabe, Takehiko; Kitajima, Masashi; Kouchi, Noriyuki; Suzuki, Isao H.

    2011-11-15

    The cross sections for the formation of the metastable atomic hydrogen in the 2s state in photoexcitation of H{sub 2} and D{sub 2} were measured as a function of the incident photon energy in the range of the doubly excited states with their symmetries of the electronic states, {sup 1}{Sigma}{sub u}{sup +} or {sup 1}{Pi}{sub u}, being resolved. It has turned out from the comparison with the cross-section curves for other dissociation processes and the theoretical calculation [J. D. Bozek et al., J. Phys. B 39, 4871 (2006)] that the Q{sub 2}{sup 1}{Pi}{sub u}(1) doubly excited state of H{sub 2} dissociates into both H(2s) + H(2p) and H(2p) + H(2p). The dissociation dynamics of this state has been discussed in terms of the nonadiabatic transition during neutral dissociations.

  2. Fragment-based configuration interaction wave function to calculate environmental effect on excited states in proteins and solutions

    NASA Astrophysics Data System (ADS)

    Hasegawa, Jun-ya

    2013-05-01

    Solvatochromic effect in proteins and solutions was described by a configuration interaction singles (CIS) wave function with fragment-localized molecular orbitals. Coarse-grained analysis indicated that the CI wave function can be described by local excitations and charge-transfer (CT) excitations between the chromophore and the environment. We developed an atomic-orbital direct runcated CIS code and applied the excited states of retinal chromophore in bacteriorhodopsin and MeOH environments, and those of s-trans-acrolein in water. Number of excitation operators was significantly reduced by eliminating the CT excitations between the environmental fragments. The truncated CIS wave functions reproduced the original excitation energies very well.

  3. Excited-state dynamics of protonated retinal Schiff base in solution

    SciTech Connect

    Logunov, S.L.; Li, S.; El-Sayed, M.A.

    1996-11-21

    The dynamics of all-trans and 13-cis retinal protonated Schiff base (RPSB) were studied in different solvents by means of picosecond transient spectroscopy. The decay time of the excited state absorption was found to be wavelength dependent due to the contribution of the faster decay of stimulated emission. The stimulated emission has a lifetime of a 2.5-4 ps while the excited state absorption decay is biexponential with lifetimes of 2.5-4 and 10-12 ps. The fluorescence quantum yield is strongly temperature dependent but viscosity has a small effect on both excited-state lifetime and fluorescence quantum yield. This leads to the conclusion that there is a {approx}600 cm{sup -1} barrier in the excited-state which results from intramolecular electronic factors and not from the solvent viscosity. The comparison of these results with those for the retinal in rhodopsin and bacteriorhodopsin is discussed in terms of the protein catalysis for the retinal photoisomerization. 31 refs., 8 figs., 2 tabs.

  4. Excited electronic states of limonene: A circular dichroism and photoelectron spectroscopy study of d-limonene

    NASA Astrophysics Data System (ADS)

    Brint, P.; Meshulam, Edna; Gedanken, Aharon

    1984-08-01

    The excited states of limonene are discussed in the light of vacuum-UV absorption, VUVCD and photoelectron spectroscopy measurements. Only one π → π* transition arising from the double bond of the ring is observed. The CD sign of the π → π* transition does not obey the octant rule formulated for chiral olefins.

  5. High-precision Stark shift measurements in excited states of indium using an atomic beam

    NASA Astrophysics Data System (ADS)

    Majumder, P. K.; Carter, A. L.; Augenbraun, B. L.; Rupasinghe, P. M.; Vilas, N. B.

    2016-05-01

    A recent precision measurement in our group of the indium scalar polarizability within the 410 nm 5p1 / 2 --> 6s1 / 2 transition showed excellent agreement with ab initio atomic theory. We are now completing a measurement of the polarizability within the 6s1 / 2 --> 6p1 / 2 excited-state transition. In our experiment, two external cavity semiconductor diode lasers interact transversely with a collimated indium atomic beam. We tune the 410 nm laser to the 5p1 / 2 --> 6s1 / 2 transition, keeping the laser locked to the exact Stark-shifted resonance frequency. We overlap a 1343 nm infrared laser to reach the 6p1 / 2 state. The very small infrared absorption in our atomic beam is detected using two-tone FM spectroscopy. Monitoring the two-step excitation signal in a field-free supplemental vapor cell provides frequency reference and calibration. Precisely calibrated electric fields of 5 - 15 kV/cm produce Stark shifts of order 100 MHz for this excited state. Experimental details, latest results, and comparison to theory will be discussed. In the near future, The same infrared laser will be tuned to 1291 nm to study the scalar and tensor polarizability of the 6p3 / 2 excited state providing a distinct test of atomic theory. Work supported by NSF Grant # 1404206.

  6. Excitation of the a {sup 3{Pi}} state of CO by electron impact

    SciTech Connect

    Ristic, M. M.; Poparic, G. B.; Belic, D. S.

    2011-04-15

    Electron impact excitation of the a {sup 3{Pi}} valence state of the carbon-monoxide molecule has been studied in the energy region from threshold to 10 eV. Excitation functions for spin forbidden transitions from the {nu}=0 level of the ground X {sup 1}{Sigma}{sup +} state of CO to the {nu}{sup '}=0, 1, 2, 3, 4, and 5 levels of the a {sup 3{Pi}} state are measured. A crossed beam double trochoidal electron spectrometer is used. Forward and backward scattered electrons from the {nu}{sup '}=0 excitation channel are separated by electron beam modulation and a time-of-flight detection technique. The present results are normalized to the ground state {sup 2{Pi}} resonance vibrational excitation cross sections and absolute values of the differential cross sections at the border angles of 0 deg. and 180 deg. are determined. In this way the differential cross section measurements are completed in the full angular range from 0 deg. to 180 deg. The present results are compared to the existing literature data.

  7. Excited states of the Calogero-Sutherland model and singular vectors of the WN algebra

    NASA Astrophysics Data System (ADS)

    Awata, Hidetoshi; Matsuo, Yutaka; Odake, Satoru; Shiraishi, Jun'ichi

    1995-02-01

    Using the collective field method, we find a relation between the Jack symmetric polynomials, which describe the excited states of the Calogero-Sutherland model, and the singular vectors of the WN algebra. Based on this relation, we obtain their integral representations. We also give a direct algebraic method which leads to the same result, and integral representations of the skew-Jack polynomials.

  8. Excited-state properties of a triply ortho-metalated iridium(III) complex

    SciTech Connect

    King, K.A.; Spellane, P.J.; Watts, R.J.

    1985-03-06

    The characterization of the ground and luminescent excited states of a triply ortho-metalated complex of ppy, fac-Ir(ppy)/sub 3/ (ppy = 2-phenylpyridine) is effected. This complex, which is the first triply ortho-metalated ppy species to be characterized, is one of the strongest transition-metal photoreductants thus far reported. 20 references, 2 figures.

  9. Infrared/ultraviolet quadruple resonance spectroscopy to investigate structures of electronically excited states

    SciTech Connect

    Weiler, M.; Bartl, K.; Gerhards, M.

    2012-03-21

    Molecular beam investigations in combination with IR/UV spectroscopy offer the possibility to obtain structural information on isolated molecules and clusters. One of the demanding tasks is the discrimination of different isomers, e.g., by the use of isomer specific UV excitations. If this discrimination fails due to overlaying UV spectra of different isomers, IR/IR methods offer another possibility. Here, we present a new IR/UV/IR/UV quadruple resonance technique to distinguish between different isomers especially in the electronically excited state. Due to the IR spectra, structural changes and photochemical pathways in excited states can be assigned and identified. The method is applied to the dihydrated cluster of 3-hydroxyflavone which has been investigated as photochemically relevant system and proton wire model in the S{sub 1} state. By applying the new IR/UV/IR/UV technique, we are able to show experimentally that both in the electronic ground (S{sub 0}) and the electronically excited state (S{sub 1}) two isomers have to be assigned.

  10. Initial excited-state dynamics of an N-alkylated indanylidene-pyrroline (NAIP) rhodopsin analog.

    PubMed

    Schapiro, Igor; Fusi, Stefania; Olivucci, Massimo; Andruniów, Tadeusz; Sasidharanpillai, Swaroop; Loppnow, Glen R

    2014-10-23

    N-Alkylated indanylidene-pyrroline-based molecular switches mimic different aspects of the light-induced retinal chromophore isomerization in rhodopsin: the vertebrate dim-light visual pigment. In particular, they display a similar ultrashort excited-state lifetime, subpicosecond photoproduct appearance time, and photoproduct vibrational coherence. To better understand the early light-induced dynamics of such systems, we measured and modeled the resonance Raman spectra of the Z-isomer of the N-methyl-4-(5'-methoxy-2',2'-dimethyl-indan-1'-ylidene)-5-methyl-2,3-dihydro-2H-pyrrolium (NAIP) switch in methanol solution. It is shown that the data, complemented with a <70 fs excited-state trajectory computation, demonstrate initial excited-state structural dynamics dominated by double-bond expansion and single-bond contraction stretches. This mode subsequently couples with the five-membered ring inversion and double-bond torsion. These results are discussed in the context of the mechanism of the excited-state photoisomerization of NAIP switches in solution and the 11-cis retinal in rhodopsin. PMID:25255466

  11. Energy conversion based on molecular excited states: Redox splitting in soluble polymers. Final report

    SciTech Connect

    Meyer, T.J.

    1995-12-31

    A general method was developed for preparing complexes of Ru(II) with three different bidentate ligands; it is being extended to monodentate ligands for more synthetic versatility. This method was used to prepare a series of complexes with pre-designed absorption properties, with the goal of ``black absorbers`` for use as antenna chromophores in a light-to-chemical energy conversion array. The energy gap law for nonradiative decay was studied for preparing near-IR luminophores with long excited state lifetimes. The problem of destructive dd excited states in Ru(II) polypyridyl complexes was focused on, with success in preparing an extremely photo-inert complex with monodentate pyridine ligands. Time-resolved resonance Raman and infrared spectroscopy were used to study subtle excited state properties of complexes of Ru(II), Os(II), and Re(I). Success was achieved in controlled immobilization of d{sup 6} chromophores and quenchers on styrenic polymers. Having perfected our synthetic technique, we have begun to optimize the ground and excited state properties such as chromophore density, dipole orientation, and lifetime.

  12. Minimal-excitation states for electron quan-tum optics using levitons

    NASA Astrophysics Data System (ADS)

    Roulleau, Preden; Jullien, Thibaut; Dubois, Julie; Portier, Fabien; Roche, Patrice; Cavanna, Antonella; Jin, Yong; Wegscheider, Werner; Glattli, D. Christian

    2014-03-01

    The on-demand generation of pure quantum excitations is important for the operation of quantum systems, but it is particularly difficult for a system of fermions. This is because any perturbation affects all states below the Fermi energy, resulting in a complex superposition of particle and hole excitations. However, it was predicted nearly 20 years ago that a Lorentzian time-dependent potential with quantized flux generates a minimal excitation with only one particle and no hole. Here we report that such quasiparticles (hereafter termed levitons) can be generated on demand in a conductor by applying voltage pulses to a contact. Partitioning the excitations with an electronic beam splitter generates a current noise that we use to measure their number. Minimal-excitation states are observed for Lorentzian pulses, whereas for other pulse shapes there are significant contributions from holes. Further identification of levitons is provided in the energy domain with shot-noise spectroscopy, and in the time domain with electronic Hong-Ou-Mandel noise correlations.

  13. The End of Superdeformation: De-excitation to Spherical States in Lead Isotopes

    NASA Astrophysics Data System (ADS)

    Cizewski, Jolie A.

    1997-04-01

    Numerous examples of superdeformed rotational bands at high angular momenta have been observed in medium and heavy mass nuclei. The A ~190 region has been especially rich - superdeformed (SD) excitations have been identified in at least 22 isotopes and a large fraction of these bands have γ-ray energies which are simply related. However, the fundamental properties of excitation energy and spin-parity have only recently between determined. The first candidate for a discrete transition which links the SD band to ``normal" deformed (ND) excitations was observed in ^194Pb.(M. J. Brinkman, et al., Phys. Rev. C53), R1461 (1996). Subsequently, many transitions which connect SD and ND excitations in ^194Hg were observed, which allowed the determination of the excitation energy and spin.footnote T. L. Khoo, et al., Phys. Rev. Lett. 76, 1583 (1996). In ^194Pb as many as 12 discrete transitionsfootnote A. Lopez-Martens, et al., Phys. Lett. B380, 18 (1996) and K. Hauschild, et al., Phys. Rev. C (1996). have now been identified with the Eurogam or Gammasphere arrays of γ-ray detectors. This has allowed model-independent determinations of the excitation energy, spin, and parity of these states. The decay of the SD to ND states has been suggested to proceed via mixing between SD and ND excitations with similar excitation energies and angular momenta,(E. Vigezzi, et al., Phys. Lett. B249), 163 (1990). and allows a probe of the complex character of excitations at moderate temperatures in the ND well. In addition, the quasi-continuous spectrum of transitions which link SD and ND excitations can be used to probe level density and pairing degrees of freedom in hot, ND nuclei.footnote T. Dossing, et al., Phys. Rev. Lett. 75, 1276 (1995); A. Lopez-Martens, et al., PRL 77, 1707 (1996); and D.P. McNabb, et al., BAPS 41, 1237 (1996). Studies of the deexcitation of SD bands will be reviewed with a focus on the Pb isotopes.

  14. Excited state dynamics in SO2. I. Bound state relaxation studied by time-resolved photoelectron-photoion coincidence spectroscopy.

    PubMed

    Wilkinson, Iain; Boguslavskiy, Andrey E; Mikosch, Jochen; Bertrand, Julien B; Wörner, Hans Jakob; Villeneuve, David M; Spanner, Michael; Patchkovskii, Serguei; Stolow, Albert

    2014-05-28

    The excited state dynamics of isolated sulfur dioxide molecules have been investigated using the time-resolved photoelectron spectroscopy and time-resolved photoelectron-photoion coincidence techniques. Excited state wavepackets were prepared in the spectroscopically complex, electronically mixed (B̃)(1)B1/(Ã)(1)A2, Clements manifold following broadband excitation at a range of photon energies between 4.03 eV and 4.28 eV (308 nm and 290 nm, respectively). The resulting wavepacket dynamics were monitored using a multiphoton ionisation probe. The extensive literature associated with the Clements bands has been summarised and a detailed time domain description of the ultrafast relaxation pathways occurring from the optically bright (B̃)(1)B1 diabatic state is presented. Signatures of the oscillatory motion on the (B̃)(1)B1/(Ã)(1)A2 lower adiabatic surface responsible for the Clements band structure were observed. The recorded spectra also indicate that a component of the excited state wavepacket undergoes intersystem crossing from the Clements manifold to the underlying triplet states on a sub-picosecond time scale. Photoelectron signal growth time constants have been predominantly associated with intersystem crossing to the (c̃)(3)B2 state and were measured to vary between 750 and 150 fs over the implemented pump photon energy range. Additionally, pump beam intensity studies were performed. These experiments highlighted parallel relaxation processes that occurred at the one- and two-pump-photon levels of excitation on similar time scales, obscuring the Clements band dynamics when high pump beam intensities were implemented. Hence, the Clements band dynamics may be difficult to disentangle from higher order processes when ultrashort laser pulses and less-differential probe techniques are implemented.

  15. Excited-state nuclear forces on adiabatic potential-energy surfaces by time-dependent density-functional theory

    NASA Astrophysics Data System (ADS)

    Haruyama, Jun; Suzuki, Takahiro; Hu, Chunping; Watanabe, Kazuyuki

    2012-01-01

    We present a simple and computationally efficient method to calculate excited-state nuclear forces on adiabatic potential-energy surfaces (APES) from linear-response time-dependent density-functional theory within a real-space framework. The Casida ansatz, which has been validated for computing first-order nonadiabatic couplings in previous studies, was applied to the calculation of the excited-state forces. Our method is validated by the consistency of results in the lower excited states, which reproduce well those obtained by the numerical derivative of each APES. We emphasize the usefulness of this technique by demonstrating the excited-state molecular-dynamics simulation.

  16. Measuring Residual Dipolar Couplings in Excited Conformational States of Nucleic Acids by CEST NMR Spectroscopy.

    PubMed

    Zhao, Bo; Zhang, Qi

    2015-10-28

    Nucleic acids undergo structural transitions to access sparsely populated and transiently lived conformational states--or excited conformational states--that play important roles in diverse biological processes. Despite ever-increasing detection of these functionally essential states, 3D structure determination of excited states (ESs) of RNA remains elusive. This is largely due to challenges in obtaining high-resolution structural constraints in these ESs by conventional structural biology approaches. Here, we present nucleic-acid-optimized chemical exchange saturation transfer (CEST) NMR spectroscopy for measuring residual dipolar couplings (RDCs), which provide unique long-range angular constraints in ESs of nucleic acids. We demonstrate these approaches on a fluoride riboswitch, where one-bond (13)C-(1)H RDCs from both base and sugar moieties provide direct structural probes into an ES of the ligand-free riboswitch.

  17. Excited-state spectroscopy of singly, doubly and triply-charmed baryons from lattice QCD

    SciTech Connect

    Padmanath, M.; Edwards, Robert G.; Mathur, Nilmani; Peardon, Michael

    2014-07-01

    We present the ground and excited state spectra of singly, doubly and triply-charmed baryons by using dynamical lattice QCD. A large set of baryonic operators that respect the symmetries of the lattice and are obtained after subduction from their continuum analogues are utilized. These operators transform as irreducible representations of SU(3)F symmetry for flavour, SU(4) symmetry for Dirac spins of quarks and O(3) symmetry for orbital angular momenta. Using novel computational techniques correlation functions of these operators are generated and the variational method is exploited to extract excited states. The lattice spectra that we obtain have baryonic states with well-defined total spins up to 7/2 and the low lying states remarkably resemble the expectations of quantum numbers from SU(6)ⓍO(3) symmetry.

  18. Energy transfer from PO excited states to alkali metal atoms in the phosphorus chemiluminescence flame

    PubMed Central

    Khan, Ahsan U.

    1980-01-01

    Phosphorus chemiluminescence under ambient conditions of a phosphorus oxidation flame is found to offer an efficient electronic energy transferring system to alkali metal atoms. The lowest resonance lines, 2P3 / 2,½→2S½, of potassium and sodium are excited by energy transfer when an argon stream at 80°C carrying potassium or sodium atoms intersects a phosphorus vapor stream, either at the flame or in the postflame region. The lowest electronically excited metastable 4IIi state of PO or the (PO[unk]PO)* excimer is considered to be the probable energy donor. The (PO[unk]PO)* excimer results from the interaction of the 4IIi state of one PO molecule with the ground 2IIr state of another. Metastability of the donor state is strongly indicated by the observation of intense sensitized alkali atom fluorescence in the postflame region. PMID:16592925

  19. Identification of the cationic excited state of cyclopentanone via time-resolved Ion yield measurements

    NASA Astrophysics Data System (ADS)

    Zuo, Wanlong; Yin, Hang; Liu, Xiaochun; Lv, Hang; Zhao, Lei; Shi, Ying; Yan, Bing; Jin, Mingxing; Ding, Dajun; Xu, Haifeng

    2016-06-01

    We report the experimental evidence of the one-photon resonance in the cationic excited state of cyclopentanone using the femtosecond time-resolved pump-probe method. The transients of the parent ion and the C2H4+ fragment exhibit constant depletion in the pump-probe delay time up to 7 ps, however, that of the C4H8+/C3H4O+ fragment presents formation behavior. By recording dependence of the ion yields as the probe laser intensity, we demonstrate one 400-nm photon resonance in the cationic excited state, which is assigned as the D4(2A) cationic state based on the theoretical calculations. Possible dissociation mechanism of the D4 state is also discussed.

  20. Communication: Excited states, dynamic correlation functions and spectral properties from full configuration interaction quantum Monte Carlo.

    PubMed

    Booth, George H; Chan, Garnet Kin-Lic

    2012-11-21

    In this communication, we propose a method for obtaining isolated excited states within the full configuration interaction quantum Monte Carlo framework. This method allows for stable sampling with respect to collapse to lower energy states and requires no uncontrolled approximations. In contrast with most previous methods to extract excited state information from quantum Monte Carlo methods, this results from a modification to the underlying propagator, and does not require explicit orthogonalization, analytic continuation, transient estimators, or restriction of the Hilbert space via a trial wavefunction. Furthermore, we show that the propagator can directly yield frequency-domain correlation functions and spectral functions such as the density of states which are difficult to obtain within a traditional quantum Monte Carlo framework. We demonstrate this approach with pilot applications to the neon atom and beryllium dimer.

  1. {beta} decay of 129Cd and excited states in 129In

    SciTech Connect

    Taprogge, J.; Jungclaus, A.; Grawe, H.; Nishimura, S.; Doornenbal, P.; Lorusso, G.; Simpson, G. S.; Soderstrom, P. A.; Sumikama, T.; Xu, Z. Y.; Kondev, F. G.

    2015-05-26

    The β decay of Cd 129 , produced in the relativistic fission of a U 238 beam, was experimentally studied at the RIBF facility at the RIKEN Nishina Center. From the γ radiation emitted after the β decays, a level scheme of In 129 was established comprising 31 excited states and 69 γ -ray transitions. The experimentally determined level energies are compared to state-of-the-art shell-model calculations. The half-lives of the two β -decaying states in Cd 129 were deduced and the β feeding to excited states in In 129 were analyzed. It is found that, as in most cases in the Z<50 , N≤82 region, both decays are dominated by the ν0g 7/2 →π0g 9/2 Gamow–Teller transition, although the contribution of first-forbidden transitions cannot be neglected.

  2. Relativistic configuration interaction calculation on the ground and excited states of iridium monoxide

    SciTech Connect

    Suo, Bingbing; Yu, Yan-Mei; Han, Huixian

    2015-03-07

    We present the fully relativistic multi-reference configuration interaction calculations of the ground and low-lying excited electronic states of IrO for individual spin-orbit component. The lowest-lying state is calculated for Ω = 1/2, 3/2, 5/2, and 7/2 in order to clarify the ground state of IrO. Our calculation suggests that the ground state is of Ω = 1/2, which is highly mixed with {sup 4}Σ{sup −} and {sup 2}Π states in Λ − S notation. The two low-lying states 5/2 and 7/2 are nearly degenerate with the ground state and locate only 234 and 260 cm{sup −1} above, respectively. The equilibrium bond length 1.712 Å and the harmonic vibrational frequency 903 cm{sup −1} of the 5/2 state are close to the experimental measurement of 1.724 Å and 909 cm{sup −1}, which suggests that the 5/2 state should be the low-lying state that contributes to the experimental spectra. Moreover, the electronic states that give rise to the observed transition bands are assigned for Ω = 5/2 and 7/2 in terms of the obtained excited energies and oscillator strengths.

  3. Nature of Electronically Excited States of Organic Compounds and Processes of Nonradiative Conversion

    NASA Astrophysics Data System (ADS)

    Mayer, G. V.; Plotnikov, V. G.; Artyukhov, V. Ya.

    2016-08-01

    Models of quantum-chemical calculation of rate constants for internal processes and intersystem crossing in polyatomic molecules are considered. The influence of the nature of electronically excited states in organic compounds is investigated. It is shown that the explicit allowance for the nature of wave functions of electronic states for estimation of electronic matrix elements of nonadiabaticity operators and spin-orbit interaction allows photophysical processes in organic compounds to be considered in detail.

  4. Different motor learning effects on excitability changes of motor cortex in muscle contraction state.

    PubMed

    Sugawara, Kenichi; Tanabe, Shigeo; Suzuki, Tomotaka; Higashi, Toshio

    2013-09-01

    We aimed to investigate whether motor learning induces different excitability changes in the human motor cortex (M1) between two different muscle contraction states (before voluntary contraction [static] or during voluntary contraction [dynamic]). For the same, using motor evoked potentials (MEPs) obtained by transcranial magnetic stimulation (TMS), we compared excitability changes during these two states after pinch-grip motor skill learning. The participants performed a force output tracking task by pinch grip on a computer screen. TMS was applied prior to the pinch grip (static) and after initiation of voluntary contraction (dynamic). MEPs of the following muscles were recorded: first dorsal interosseous (FDI), thenar muscle (Thenar), flexor carpi radialis (FCR), and extensor carpi radialis (ECR) muscles. During both the states, motor skill training led to significant improvement of motor performance. During the static state, MEPs of the FDI muscle were significantly facilitated after motor learning; however, during the dynamic state, MEPs of the FDI, Thenar, and FCR muscles were significantly decreased. Based on the results of this study, we concluded that excitability changes in the human M1 are differentially influenced during different voluntary contraction states (static and dynamic) after motor learning.

  5. Ligand-ligand charge-transfer excited states of Os(II) complexes

    SciTech Connect

    Perkins, T.A.; Schanze, K.S. ); Pourreau, D.B.; Netzel, T.L. )

    1989-06-01

    This paper examines the photophysics of metal-to-ligand charge-transfer (MLCT) and ligand-to-ligand charge-transfer (LLCT) excited states in a series of ((bpy){sub 2}Os{sup II}(CO)L){sup 2+} (Os-L) complexes. For each of the complexes studied, the d{pi}(Os) {yields} {pi}*(bpy) absorption band is the lowest energy transition that is apparent. For L = pyridine and benzonitrile, only long-lived, highly luminescent MLCT states are observed. However, when L = an electron-donor aminobenzonitrile (ABN) species (DMABN, TMABN, or CMI; see text), MLCT emission is quenched and in < 30 ps LLCT excited states are formed, *((bpy{sup {sm bullet}{minus}})-(bpy)OS{sup II}(CO)ABN{sup {sm bullet}+}){sup 2+}. The observed, weight-average radiationless decays of the LLCT excited states in acetonitrile and dichloromethane follow the squence Os-DMABN < Os-TMABN < Os-CMI in each solvent, and the calculated energies of the LLCT states for these complexes are in inverse order to the decay rates as expected if an energy gap law is followed. Finally, multiexponential relaxations of the LLCT states are pronounced in the nonpolar solvent dichloromethane. The dependence of these relaxations on the concentration of added electrolyte suggests that they may be due to ion-pair structure and dynamics.

  6. Quantum-chemical study of electronically excited states of protolytic forms of vanillic acid

    NASA Astrophysics Data System (ADS)

    Vusovich, O. V.; Tchaikovskaya, O. N.; Sokolova, I. V.; Vasil'eva, N. Y.

    2015-12-01

    The paper describes an analysis of possible ways of deactivation of electronically excited states of 4-hydroxy- 3-methoxy-benzoic acid (vanillic acid) and its protolytic forms with the use of quantum-chemical methods INDO/S (intermediate neglect of differential overlap with a spectroscopic parameterization) and MEP (molecular electrostatic potential). The ratio of radiative and non-radiative deactivation channels of the electronic excitation energy is established. The rate constants of photophysical processes (internal and intercombination conversions) occurring after the absorption of light in these forms are evaluated.

  7. Neutron correlations in the decay of the first excited state of 11Li

    NASA Astrophysics Data System (ADS)

    Smith, J. K.; Baumann, T.; Bazin, D.; Brown, J.; DeYoung, P. A.; Frank, N.; Jones, M. D.; Kohley, Z.; Luther, B.; Marks, B.; Spyrou, A.; Stephenson, S. L.; Thoennessen, M.; Volya, A.

    2016-11-01

    The decay of unbound excited 11Li was measured after being populated by a two-proton removal from a 13B beam at 71 MeV/nucleon. Decay energy spectra and Jacobi plots were obtained from measurements of the momentum vectors of the 9Li fragment and neutrons. A resonance at an excitation energy of ∼1.2 MeV was observed. The kinematics of the decay are equally well fit by a simple dineutron-like model or a phase-space model that includes final state interactions. A sequential decay model can be excluded.

  8. Assessing Accuracy of Exchange-Correlation Functionals for the Description of Atomic Excited States

    NASA Astrophysics Data System (ADS)

    Makowski, Marcin; Hanas, Martyna

    2016-09-01

    The performance of exchange-correlation functionals for the description of atomic excitations is investigated. A benchmark set of excited states is constructed and experimental data is compared to Time-Dependent Density Functional Theory (TDDFT) calculations. The benchmark results show that for the selected group of functionals good accuracy may be achieved and the quality of predictions provided is competitive to computationally more demanding coupled-cluster approaches. Apart from testing the standard TDDFT approaches, also the role of self-interaction error plaguing DFT calculations and the adiabatic approximation to the exchange-correlation kernels is given some insight.

  9. The Yb-doped aluminosilicate fibers photodarkening mechanism based on the charge-transfer state excitation

    NASA Astrophysics Data System (ADS)

    Rybaltovsky, A. A.; Bobkov, K. K.; Velmiskin, V. V.; Umnikov, A. A.; Shestakova, I. A.; Guryanov, A. N.; Likhachev, M. E.; Bubnov, M. M.; Dianov, E. M.

    2014-03-01

    We have studied the photodarkening effect in fiber preforms with an ytterbium-doped aluminosilicate glass core. The room-temperature stable Yb2+ ions formation in the glass matrix under both UV- and NIR-pumping irradiation was revealed by the method of absorption spectra analysis and the fluorescence spectroscopy technique. Comparative studies of preforms and crystals samples luminescence spectra, obtained under UV-excitation, were performed. A general mechanism of Yb2+ ions and aluminium oxygen-hole centers (Al-OHC) formation as a result of photoinduced process of Yb3+ ions excitation to "charge-transfer state" (CTS) was found for both Yb:YAG crystal and aluminosilicate glass.

  10. Analysis of strongly coupled electronic states in diatomic molecules: Low-lying excited states of RbCs

    SciTech Connect

    Bergeman, T.; Fellows, C.E.; Gutterres, R.F.; Amiot, C.

    2003-05-01

    Analysis and assignment of spectra involving the lowest excited states of the heavier alkali-metal atom dimers are complicated by the strong spin-orbit coupling elements. Here we report an analysis of the Fourier-transform spectroscopy data from laser-induced fluorescence of the coupled A {sup 1}{sigma}{sup +} and b {sup 3}{pi} states of RbCs, using the discrete variable representation. Fitted parameters are given and special effects due to strong coupling are discussed.

  11. Ab initio study on electronically excited states of lithium isocyanide, LiNC

    NASA Astrophysics Data System (ADS)

    Yasumatsu, Hisato; Jeung, Gwang-Hi

    2014-01-01

    The electronically excited states of the lithium isocyanide molecule, LiNC, were studied by means of ab initio calculations. The bonding nature of LiNC up to ˜10 eV is discussed on the basis of the potential energy surfaces according to the interaction between the ion-pair and covalent states. The ion-pair states are described by Coulomb attractive interaction in the long distance range, while the covalent ones are almost repulsive or bound with a very shallow potential dent. These two states interact each other to form adiabatic potential energy surfaces with non-monotonic change in the potential energy with the internuclear distance.

  12. Time-resolved study of excited states of N2 near its first ionization threshold

    NASA Astrophysics Data System (ADS)

    Moise, Angelica; Prince, Kevin C.; Richter, Robert

    2011-03-01

    Two-photon, two-color double-resonance ionization spectroscopy combining synchrotron vacuum ultraviolet radiation with a tunable near-infrared (NIR) laser has been used to investigate gerade symmetry states of the nitrogen molecule. The rotationally resolved spectrum of an autoionizing 1Σg- state has been excited via the intermediate c4 (v = 0) 1Πu Rydberg state. We present the analysis of the band located at Tv = 10 800.7 ± 2 cm-1 with respect to the intermediate state, 126 366 ± 11 cm-1 with respect to the ground state, approximately 700 cm-1 above the first ionization threshold. From the analysis a rotational constant of Bv = 1.700 ± 0.005 cm-1 has been determined for this band. Making use of the pulsed structure of the two radiation beams, lifetimes of several rotational levels of the intermediate state have been measured. We also report rotationally-averaged fluorescence lifetimes (300 K) of several excited electronic states accessible from the ground state by absorption of one photon in the range of 13.85-14.9 eV. The averaged lifetimes of the c4 (0) and c5 (0) states are 5.6 and 4.4 ns, respectively, while the b' (12), c'4 (4, 5, 6), and c'5 (0) states all have lifetimes in the range of hundreds of picoseconds.

  13. Role of excited state solvent fluctuations on time-dependent fluorescence Stokes shift

    SciTech Connect

    Li, Tanping E-mail: revatik@lsu.edu; Kumar, Revati E-mail: revatik@lsu.edu

    2015-11-07

    We explore the connection between the solvation dynamics of a chromophore upon photon excitation and equilibrium fluctuations of the solvent. Using molecular dynamics simulations, fluorescence Stokes shift for the tryptophan in Staphylococcus nuclease was examined using both nonequilibrium calculations and linear response theory. When the perturbed and unperturbed surfaces exhibit different solvent equilibrium fluctuations, the linear response approach on the former surface shows agreement with the nonequilibrium process. This agreement is excellent when the perturbed surface exhibits Gaussian statistics and qualitative in the case of an isomerization induced non-Gaussian statistics. However, the linear response theory on the unperturbed surface breaks down even in the presence of Gaussian fluctuations. Experiments also provide evidence of the connection between the excited state solvent fluctuations and the total fluorescence shift. These observations indicate that the equilibrium statistics on the excited state surface characterize the relaxation dynamics of the fluorescence Stokes shift. Our studies specifically analyze the Gaussian fluctuations of the solvent in the complex protein environment and further confirm the role of solvent fluctuations on the excited state surface. The results are consistent with previous investigations, found in the literature, of solutes dissolved in liquids.

  14. Coherent Excitation of Lithium to Rydberg States and Application to Rydberg Atom Optics

    NASA Astrophysics Data System (ADS)

    Stevens, G.; Widmer, M.; Tudorica, F.; Iu, C.-H.; Metcalf, H.

    1996-05-01

    We present a theoretical analysis of several schemes for coherently exciting lithium atoms in a thermal beam to Rydberg states in a four level/three laser system, previously discussed by Oreg et al.(J. Oreg et al.), Phys. Rev. A 45, 4888 (1992). The time evolution of the dressed states and their populations are calculated numerically, solving the optical Bloch equations by a fourth order Runge-Kutta integration. Our code closely models actual experimental conditions, including spontaneous decay, beam profiles, intensities and detunings. Large Rydberg populations (50%) around n=15 may be obtained by non-adiabatic excitation, with each laser power on the order of 1 mW. We discuss the effects of an externally controlled time dependent detuning in the Rydberg state, for example as produced by atoms traversing an inhomogeneous electric field. An understanding of this excitation mechanism is important for large angle reflection of coherently excited atoms using field gradients. Some primitive ideas of Stark-Rydberg atom optics are presented.

  15. Excited state polarizabilities for CC2 using the resolution-of-the-identity approximation.

    PubMed

    Graf, Nora K; Friese, Daniel H; Winter, Nina O C; Hättig, Christof

    2015-12-28

    We report an implementation of static and frequency-dependent excited state polarizabilities for the approximate coupled cluster single and doubles model CC2 as analytic second derivatives of an excited state quasienergy Lagrangian. By including appropriate conditions for the normalization and the phase of the eigenvectors, divergent secular terms are avoided. This leads to response equations in a subspace orthogonal to the unperturbed eigenvectors. It is shown how these projected equations can be solved without storage of the double excitation part of the eigenvectors. By exploiting the resolution-of-the-identity approximation and a numerical Laplace transformation, the quadratic scaling of the main memory demands of RI-CC2 with the system size could be preserved. This enables calculations of excited state polarizabilities for large molecules, e.g., linear polyacenes up to decacene with almost 2500 basis functions on a single compute node within a few days. For a test set of molecules where measurements are available as reference data, we compare the orbital-relaxed and unrelaxed CC2 approaches with experiment to validate its accuracy. The approach can be easily extended to other response methods, in particular CIS(D∞). The latter gives results which, in the orbital-relaxed case, are within a few percent of the CC2 values, while coupled cluster singles results deviate typically by about 20% from orbital-relaxed CC2 and experimental reference data. PMID:26723652

  16. Observation of excited state charge transfer with fs/ps-CARS

    SciTech Connect

    Blom, Alex Jason

    2009-01-01

    Excited state charge transfer processes are studied using the fs/ps-CARS probe technique. This probe allows for multiplexed detection of Raman active vibrational modes. Systems studied include Michler's Ketone, Coumarin 120, 4-dimethylamino-4'-nitrostilbene, and several others. The vibrational spectrum of the para di-substituted benzophenone Michler's Ketone in the first excited singlet state is studied for the first time. It is found that there are several vibrational modes indicative of structural changes of the excited molecule. A combined experimental and theoretical approach is used to study the simplest 7-amino-4-methylcoumarin, Coumarin 120. Vibrations observed in FTIR and spontaneous Raman spectra are assigned using density functional calculations and a continuum solvation model is used to predict how observed modes are affected upon inclusion of a solvent. The low frequency modes of the excited state charge transfer species 4-dimethylamino-4{prime}-nitrostilbene are studied in acetonitrile. Results are compared to previous work on this molecule in the fingerprint region. Finally, several partially completed projects and their implications are discussed. These include the two photon absorption of Coumarin 120, nanoconfinement in cyclodextrin cavities and sensitization of titania nanoparticles.

  17. Red and blue shift of liquid water's excited states: A many body perturbation study

    NASA Astrophysics Data System (ADS)

    Ziaei, Vafa; Bredow, Thomas

    2016-08-01

    In the present paper, accurate optical absorption spectrum of liquid H2O is calculated in the energy range of 5-20 eV to probe the nature of water's excited states by means of many body perturbation approach. Main features of recent inelastic X-ray measurements are well reproduced, such as a bound excitonic peak at 7.9 eV with a shoulder at 9.4 eV as well as the absorption maximum at 13.9 eV, followed by a broad shoulder at 18.4 eV. The spectrum is dominated by excitonic effects impacting the structures of the spectrum at low and higher energy regimes mixed by single particle effects at high energies. The exciton distribution of the low-energy states, in particular of S1, is highly anisotropic and localized mostly on one water molecule. The S1 state is essentially a HOCO-LUCO (highest occupied crystal orbital - lowest unoccupied crystal orbital) transition and of intra-molecular type, showing a localized valence character. Once the excitation energy is increased, a significant change in the character of the electronically excited states occurs, characterized through emergence of multiple quasi-particle peaks at 7.9 eV in the quasi-particle (QP) transition profile and in the occurring delocalized exciton density distribution, spread over many more water molecules. The exciton delocalization following a change of the character of excited states at around 7.9 eV causes the blue shift of the first absorption band with respect to water monomer S1. However, due to reduction of the electronic band gap from gas to liquid phase, following enhanced screening upon condensation, the localized S1 state of liquid water is red-shifted with respect to S1 state of water monomer. For higher excitations, near vertical ionization energy (11 eV), quasi-free electrons emerge, in agreement with the conduction band electron picture. Furthermore, the occurring red and blue shift of the excited states are independent of the coupling of resonant and anti-resonant contributions to the

  18. Ultrafast Excited-State Dynamics of 6-Azauracil Studied by Femtosecond Transient Absorption Spectroscopy.

    PubMed

    Hua, XinZhong; Hua, LinQiang; Liu, XiaoJun

    2015-12-31

    The excited-state dynamics of 6-azauracil in different solvents have been studied using femtosecond transient absorption spectroscopy. The molecule is populated to the S2 state with a pump pulse at 264 nm. Broad-band white light continuum which covers from 320 to 600 nm is used as the probe. With a global fitting analysis of the measured transient spectra, three decay time constants, i.e., <0.3, 5.2 ± 0.1, and >1000 ps, are directly obtained in the solvent of acetonitrile. These newly observed lifetime constants are important in clarifying its decay dynamics as well as in providing a criterion for the ultrafast dynamics simulations in 6-azauracil using quantum chemical theories. In combination with previous theoretical works, the main decay channel is proposed: the initially populated S2 decays to S1 through internal conversion in <0.3 ps, followed by an intersystem crossing from S1 to T1 in 5.2 ± 0.1 ps. The >1000 ps component is due to the decay of the T1 state. A comparison of the excited-state dynamics in different solvents reveals that the decay from S1 to T1 shows a clear dependence on the polarity of the solvents. With higher polarity, the S1 excited state decays faster. This observation is in line with the prediction by Etinski et al. [ Phys. Chem. Chem. Phys. 2010 , 12 , 15665 - 15671 ], where a blue-shift of the T1 state potential energy surface leading to an increase of the intersystem crossing rate was proposed. With the new information obtained in the present measurement, a clearer picture of the decay dynamics of 6-azauracil on the S2 excited state is provided.

  19. Excited states of the high-frequency vibrational modes and kinetics of ultrafast photoinduced electron transfer

    NASA Astrophysics Data System (ADS)

    Barykov, V. Yu.; Ivanov, A. I.

    2016-02-01

    The effect of the carrier frequency of the exciting laser pulse on the kinetics of intramolecular photoinduced charge transfer in the multi-channel stochastic model is studied. It is shown that the population of different states of high-frequency intramolecular modes upon varying the frequency of the excitation pulse can considerably alter the rate constant of ultrafast charge transfer. It is found that a negative vibrational spectral effect is expected in the vicinity of a barrier-free area (the rate constant of photoinduced charge transfer decreases along with the carrier frequency of the excitation pulse), while a positive effect is predicted in areas of high and low exergonicity (an inverse dependence). It is concluded that the value of the spectral effect falls along with the time of vibrational relaxation. For ultrafast photo-induced charge transfer, however, it remains considerable up to relaxation times of 100 fs.

  20. Ultrafast dynamics of excited state of phenoxy-phthalocyanines in solution

    NASA Astrophysics Data System (ADS)

    Yao, Cheng-Bao; Yan, Xiao-Yan; Sun, Da-Wei; Sui, Yan-Li; Li, Jin; Sun, Wen-Jun; Li, Qiang-Hua; Yang, Shou-Bin

    2016-01-01

    Ultrafast dynamics of the excited state of 2,9,16,23-phenoxy-phthalocyanine (Pc1) and 2,9,16,23-phenoxy-phthalocyanine-zinc (Pc2) has been investigated using femtosecond transient absorption (TA) and time-resolved fluorescence (TRFL) techniques. The observed dynamics of femtosecond TA and TRFL experiments are similar, which demonstrated the intrinsic properties of the excitation and the relaxation processes in both kinds of phthalocyanines with two decay components. A multi level model has been proposed to explain the photophysical processes after Soret-band excitation. The results show that the fast decay component dynamics comes from the intramolecular vibrational relaxation, the slower ones from the internal conversion. The samples are expected to be a potential candidate for optical applications and photodynamic therapy.