Energy transfer of highly vibrationally excited biphenyl.

PubMed

Hsu, Hsu Chen; Dyakov, Yuri; Ni, Chi-Kung

2010-11-07

The energy transfer between Kr atoms and highly vibrationally excited, rotationally cold biphenyl in the triplet state was investigated using crossed-beam/time-of-flight mass spectrometer/time-sliced velocity map ion imaging techniques. Compared to the energy transfer of naphthalene, energy transfer of biphenyl shows more forward scattering, less complex formation, larger cross section for vibrational to translational (V→T) energy transfer, smaller cross section for translational to vibrational and rotational (T→VR) energy transfer, larger total collisional cross section, and more energy transferred from vibration to translation. Significant increase in the large V→T energy transfer probabilities, termed supercollisions, was observed. The difference in the energy transfer of highly vibrationally excited molecules between rotationally cold naphthalene and rotationally cold biphenyl is very similar to the difference in the energy transfer of highly vibrationally excited molecules between rotationally cold naphthalene and rotationally hot naphthalene. The low-frequency vibrational modes with out-of-plane motion and rotationlike wide-angle motion are attributed to make the energy transfer of biphenyl different from that of naphthalene.

Simultaneously exciting two atoms with photon-mediated Raman interactions

NASA Astrophysics Data System (ADS)

Zhao, Peng; Tan, Xinsheng; Yu, Haifeng; Zhu, Shi-Liang; Yu, Yang

2017-06-01

We propose an approach to simultaneously excite two atoms by using a cavity-assisted Raman process in combination with a cavity-photon-mediated interaction. The system consists of a two-level atom and a Λ -type or V -type three-level atom, which are coupled together with a cavity mode. Having derived the effective Hamiltonian, we find that under certain circumstances a single photon can simultaneously excite two atoms. In addition, multiple photons and even a classical field can also simultaneously excite two atoms. As an example, we show a scheme to realize our proposal in a circuit QED setup, which is artificial atoms coupled with a cavity. The dynamics and the quantum-statistical properties of the process are investigated with experimentally feasible parameters.

Excited State Atom-Ion Charge-Exchange

NASA Astrophysics Data System (ADS)

Li, Ming; Makrides, Constantinos; Petrov, Alexander; Kotochigova, Svetlana

2017-04-01

We theoretically investigate the exothermic charge-exchange reaction between an excited atom and a ground-state positive ion. In particular, we focus on MOT-excited Ca*(4s4p 1P) atoms colliding with ground-state Yb+ ions, which are under active study by the experimental group of E. Hudson at UCLA. Collisions between an excited atom and an ion are guided by two major contributions to the long-range interaction potentials, the induction C4 /R4 and charge-quadrupole C3 /R3 potentials, and their coupling by the electron-exchange interaction. Our model of these forces leads to close-coupling equations for multiple reaction channels. We find several avoided crossings between the potentials that couple to the nearby asymptotic limits of Yb*+Ca+, some of which can possibly provide large charge exchange rate coefficients above 10-10 cm3 / s. We acknowledge support from the US Army Research Office, MURI Grants W911NF-14-1-0378 and the US National Science Foundation, Grant PHY-1619788.

Product energy distributions and energy partitioning in O atom reactions on surfaces

NASA Technical Reports Server (NTRS)

Halpern, Bret; Kori, Moris

1987-01-01

Surface reactions involving O atoms are likely to be highly exoergic, with different consequences if energy is channeled mostly to product molecules or surface modes. Thus the surface may become a source of excited species which can react elsewhere, or a sink for localized heat deposition which may disrupt the surface. The vibrational energy distribution of the product molecule contains strong clues about the flow of released energy. Two instructive examples of energy partitioning at surfaces are the Pt catalyzed oxidations: (1) C(ads) + O(ads) yields CO* (T is greater than 1000 K); and (2) CO(ads) + O(gas) yields CO2* (T is approx. 300 K). The infrared emission spectra of the excited product molecules were recorded and the vibrational population distributions were determined. In reaction 1, energy appeared to be statistically partitioned between the product CO and several Pt atoms. In reaction 2, partitioning was non-statistical; the CO2 asymmetric stretch distribution was inverted. In gas reactions these results would indicate a long lived and short lived activated complex. The requirement that Pt be heated in O atoms to promote reaction of atomic O and CO at room temperature is specifically addressed. Finally, the fraction of released energy that is deposited in the catalyst is estimated.

Minima in generalized oscillator strengths for initially excited hydrogen-like atoms

NASA Technical Reports Server (NTRS)

Matsuzawa, M.; Omidvar, K.; Inokuti, M.

1976-01-01

Generalized oscillator strengths for transitions from an initially excited state of a hydrogenic atom to final states (either discrete or continuum) have complicated structures, including minima and shoulders, as functions of the momentum transfer. Extensive calculations carried out in the present work have revealed certain systematics of these structures. Some implications of the minima to the energy dependence of the inner-shell ionization cross section of heavy atoms by proton impact are discussed.

Dissociative excitation of the manganese atom quartet levels by collisions e-MnBr2

NASA Astrophysics Data System (ADS)

Smirnov, Yu M.

2017-04-01

Dissociative excitation of quartet levels of the manganese atom was studied in collisions of electrons with manganese dibromide molecules. Eighty-two cross-sections for transitions originating at odd levels and eleven cross-sections for transitions originating at even levels have been measured at an incident electron energy of 100 eV. An optical excitation function has been recorded in the electron energy range of 0-100 eV for transitions originating from 3d 64p z 4 F° levels. For the majority of transitions, a comparison of the resulting cross-section values to cross-sections produced by direct excitation is provided.

Zoo of Quantum Phases and Excitations of Cold Bosonic Atoms in Optical Lattices

DOE Office of Scientific and Technical Information (OSTI.GOV)

Alon, Ofir E.; Streltsov, Alexej I.; Cederbaum, Lorenz S.

Quantum phases and phase transitions of weakly to strongly interacting bosonic atoms in deep to shallow optical lattices are described by a single multiorbital mean-field approach in real space. For weakly interacting bosons in one dimension, the critical value of the superfluid to Mott insulator (MI) transition found is in excellent agreement with many-body treatments of the Bose-Hubbard model. For strongly interacting bosons (i) additional MI phases appear, for which two (or more) atoms residing in each site undergo a Tonks-Girardeau-like transition and localize, and (ii) on-site excitation becomes the excitation lowest in energy. Experimental implications are discussed.

Three-photon Gaussian-Gaussian-Laguerre-Gaussian excitation of a localized atom to a highly excited Rydberg state

NASA Astrophysics Data System (ADS)

Mashhadi, L.

2017-12-01

Optical vortices are currently one of the most intensively studied topics in light-matter interaction. In this work, a three-step axial Doppler- and recoil-free Gaussian-Gaussian-Laguerre-Gaussian (GGLG) excitation of a localized atom to the highly excited Rydberg state is presented. By assuming a large detuning for intermediate states, an effective quadrupole excitation related to the Laguerre-Gaussian (LG) excitation to the highly excited Rydberg state is obtained. This special excitation system radially confines the single highly excited Rydberg atom independently of the trapping system into a sharp potential landscape into the so-called ‘far-off-resonance optical dipole-quadrupole trap’ (FORDQT). The key parameters of the Rydberg excitation to the highly excited state, namely the effective Rabi frequency and the effective detuning including a position-dependent AC Stark shift, are calculated in terms of the basic parameters of the LG beam and of the polarization of the excitation lasers. It is shown that the obtained parameters can be tuned to have a precise excitation of a single atom to the desired Rydberg state as well. The features of transferring the optical orbital and spin angular momentum of the polarized LG beam to the atom via quadrupole Rydberg excitation offer a long-lived and controllable qudit quantum memory. In addition, in contrast to the Gaussian laser beam, the doughnut-shaped LG beam makes it possible to use a high intensity laser beam to increase the signal-to-noise ratio in quadrupole excitation with minimized perturbations coming from stray light broadening in the last Rydberg excitation process.

Rydberg excitation of cold atoms inside a hollow-core fiber

NASA Astrophysics Data System (ADS)

Langbecker, Maria; Noaman, Mohammad; Kjærgaard, Niels; Benabid, Fetah; Windpassinger, Patrick

2017-10-01

We report on a versatile, highly controllable hybrid cold Rydberg atom fiber interface, based on laser cooled atoms transported into a hollow-core kagome crystal fiber. Our experiments demonstrate the feasibility of exciting cold Rydberg atoms inside a hollow-core fiber and we study the influence of the fiber on Rydberg electromagnetically induced transparency (EIT) signals. Using a temporally resolved detection method to distinguish between excitation and loss, we observe two different regimes of the Rydberg excitations: one EIT regime and one regime dominated by atom loss. These results are a substantial advancement towards future use of our system for quantum simulation or information.

Deviation from Boltzmann distribution in excited energy levels of singly-ionized iron in an argon glow discharge plasma for atomic emission spectrometry

NASA Astrophysics Data System (ADS)

Zhang, Lei; Kashiwakura, Shunsuke; Wagatsuma, Kazuaki

2012-01-01

A Boltzmann plot for many iron ionic lines having excitation energies of 4.7-9.1 eV was investigated in an argon glow discharge plasma when the discharge parameters, such as the voltage/current and the gas pressure, were varied. A Grimm-style radiation source was employed in a DC voltage range of 400-800 V at argon pressures of 400-930 Pa. The plot did not follow a linear relationship over a wide range of the excitation energy, but it yielded a normal Boltzmann distribution in the range of 4.7-5.8 eV and a large overpopulation in higher-lying excitation levels of iron ion. A probable reason for this phenomenon is that excitations for higher excited energy levels of iron ion would be predominantly caused by non-thermal collisions with argon species, the internal energy of which is received by iron atoms for the ionization. Particular intense ionic lines, which gave a maximum peak of the Boltzmann plot, were observed at an excitation energy of ca. 7.7 eV. They were the Fe II 257.297-nm and the Fe II 258.111-nm lines, derived from the 3d54s4p 6P excited levels. The 3d54s4p 6P excited levels can be highly populated through a resonance charge transfer from the ground state of argon ion, because of good matching in the excitation energy as well as the conservation of the total spin before and after the collision. An enhancement factor of the emission intensity for various Fe II lines could be obtained from a deviation from the normal Boltzmann plot, which comprised the emission lines of 4.7-5.8 eV. It would roughly correspond to a contribution of the charge transfer excitation to the excited levels of iron ion, suggesting that the charge-transfer collision could elevate the number density of the corresponding excited levels by a factor of ca.104. The Boltzmann plots give important information on the reason why a variety of iron ionic lines can be emitted from glow discharge plasmas.

Nonradiative transport of atomic excitation in Na vapor

NASA Astrophysics Data System (ADS)

Zajonc, Arthur G.; Phelps, A. V.

1981-05-01

Measurements are reported which show the effect of nonradiative losses at a gas-window interface on the backscattered fluorescence intensity for Na vapor at frequencies in the vicinity of the resonance lines near 589 nm. The Na 3P12,32 states are excited with a low-intensity single-mode tunable dye laser at high Na densities and the frequency integral of the backscattered fluorescence intensity in the D1 and D2 lines is measured. As the laser is tuned through resonance, the loss of atomic excitation to the window appears as a sharp decrease in the frequency-integrated fluorescence intensity. For example, at 7×1020 atoms m-3 the fluorescence intensity decreases by a factor of 4 in a frequency interval of 4 GHz. Measured absolute fluorescence intensities versus laser frequency are compared with predictions made using the theory of Hummer and Kunasz which includes both radiative and nonradiative transport processes. The agreement between theory and experiment is remarkably good when one considers that the theory contains only one unknown coefficient, i.e., the reflection coefficient for excited atoms at the windows. In our case the excited atoms are assumed to be completely destroyed at the window.

Non-equilibrium kinetics of plasma-assisted combustion: the role of electronically excited atoms and molecules

NASA Astrophysics Data System (ADS)

Popov, Nikolay

2016-09-01

A review of experimental and theoretical investigations of the effect of electronically excited atoms and molecules on the induction delay time and on the shift of the ignition temperature threshold of combustible mixtures is presented. At relatively low initial gas temperature, the effect of excited O(1D) atoms on the oxidation and reforming of combustible mixtures is quite significant due to the high rates of reactions of O(1D) atoms with hydrogen and hydrocarbon molecules. The singlet oxygen molecules, O2(a1Δg) , participate both in chain initiation and chain branching reactions, but the effect of O2(a1Δg) in the ignition processes is generally less important compared to the oxygen atoms. To reduce the ignition delay time and decrease the temperature threshold of fuel-air mixtures, the use of gas discharges with relatively high E/N values is recommended. In this case the reactions of electronically excited N2(A3Σu+ , B3πg , C3πu , a'1Σu-) molecules, and atomic particles in ground and electronically excited states are extremely important. The energy stored in electronic excitation of atoms and molecules is spent on the additional dissociation of oxygen and fuel molecules, on the fast gas heating, and finally to the triggering of chain branching reactions. This work was partially supported by AOARD AFOSR, FA2386-13-1-4064 grant and Linked International Laboratory LIA KaPPA (France-Russia).

Plasmon excitations in doped square-lattice atomic clusters

NASA Astrophysics Data System (ADS)

Wang, Yaxin; Yu, Ya-Bin

2017-12-01

Employing the tight-binding model, we theoretically study the properties of the plasmon excitations in doped square-lattice atomic clusters. The results show that the dopant atoms would blur the absorption spectra, and give rise to extra plasmon resonant peaks as reported in the literature; however, our calculated external-field induced oscillating charge density shows that no obvious evidences indicate the so-called local mode of plasmon appearing in two-dimensional-doped atomic clusters, but the dopants may change the symmetry of the charge distribution. Furthermore, we show that the disorder of the energy level due to dopant makes the absorption spectrum has a red- or blue-shift, which depends on the position of impurities; disorder of hopping due to dopant makes a blue- or red-shift, a larger (smaller) hopping gives a blue-shift (red-shift); and a larger (smaller) host-dopant and dopant-dopant intersite coulomb repulsion induces a blue-shift (red-shift).

Hong-Ou-Mandel Interference between Two Deterministic Collective Excitations in an Atomic Ensemble

NASA Astrophysics Data System (ADS)

Li, Jun; Zhou, Ming-Ti; Jing, Bo; Wang, Xu-Jie; Yang, Sheng-Jun; Jiang, Xiao; Mølmer, Klaus; Bao, Xiao-Hui; Pan, Jian-Wei

2016-10-01

We demonstrate deterministic generation of two distinct collective excitations in one atomic ensemble, and we realize the Hong-Ou-Mandel interference between them. Using Rydberg blockade we create single collective excitations in two different Zeeman levels, and we use stimulated Raman transitions to perform a beam-splitter operation between the excited atomic modes. By converting the atomic excitations into photons, the two-excitation interference is measured by photon coincidence detection with a visibility of 0.89(6). The Hong-Ou-Mandel interference witnesses an entangled NOON state of the collective atomic excitations, and we demonstrate its two times enhanced sensitivity to a magnetic field compared with a single excitation. Our work implements a minimal instance of boson sampling and paves the way for further multimode and multiexcitation studies with collective excitations of atomic ensembles.

Atomic Rearrangements in Electron Attachment to Laser-Excited Molecules^*

NASA Astrophysics Data System (ADS)

Pinnaduwage, Lal; McCorkle, Dennis

1996-10-01

We report the observation of extensive atomic rearrangements in dissociative electron attachment to triethylamine " (Pinnaduwage and McCorkle, Chem.Phys. Lett. (in press, 1996))" and benzene laser excited to energies above their ionization thresholds. Large signal of "rearranged" negative ions, such as C_3^- (which is observed in both cases), were observed. This is in contrast to negative-ion formation via electron attachment to molecules in their ground states, where "rearranged" negative ions are comparatively weak and have been observed only occasionally. However, formation of "rearranged" positive ions is of common occurrence in the ionization of polyatomic molecules; it is possible that the formation of "rearranged" positive ions in the ionization processes, and the formation of such negative ions via electron attachment to excited states located close to the ionization threshold, are related. * Work supported by the LDRD Program of the Oak Ridge National Laboratory, managed by Lockheed Martin Energy Research Corp. for the US Department of Energy under contract number DE-AC05-96OR22464, and by the National Science Foundation under contract CHE-93113949 with the Univ. of Tenn., Knoxville.

Hyperfine excitation of CH in collisions with atomic and molecular hydrogen

NASA Astrophysics Data System (ADS)

Dagdigian, Paul J.

2018-04-01

We investigate here the excitation of methylidene (CH) induced by collisions with atomic and molecular hydrogen (H and H2). The hyperfine-resolved rate coefficients were obtained from close coupling nuclear-spin-free scattering calculations. The calculations are based upon recent, high-accuracy calculations of the CH(X2Π)-H(2S) and CH(X2Π)-H2 potential energy surfaces. Cross-sections and rate coefficients for collisions with atomic H, para-H2, and ortho-H2 were computed for all transitions between the 32 hyperfine levels for CH(X2Π) involving the n ≤ 4 rotational levels for temperatures between 10 and 300 K. These rate coefficients should significantly aid in the interpretation of astronomical observations of CH spectra. As a first application, the excitation of CH is simulated for conditions in typical molecular clouds.

Two-photon-excited fluorescence spectroscopy of atomic fluorine at 170 nm

NASA Technical Reports Server (NTRS)

Herring, G. C.; Dyer, Mark J.; Jusinski, Leonard E.; Bischel, William K.

1988-01-01

Two-photon-excited fluorescence spectroscopy of atomic fluorine is reported. A doubled dye laser at 286-nm is Raman shifted in H2 to 170 nm (sixth anti-Stokes order) to excite ground-state 2P(0)J fluorine atoms to the 2D(0)J level. The fluorine atoms are detected by one of two methods: observing the fluorescence decay to the 2PJ level or observing F(+) production through the absorption of an additional photon by the excited atoms. Relative two-photon absorption cross sections to and the radiative lifetimes of the 2D(0)J states are measured.

Excitation of the 229 m Th nuclear isomer via resonance conversion in ionized atoms

NASA Astrophysics Data System (ADS)

Karpeshin, F. F.; Trzhaskovskaya, M. B.

2015-09-01

Pressing problems concerning the optical pumping of the 7.6-eV 229 m Th nuclear isomer, which is a candidate for a new nuclear optical reference point for frequencies, are examined. Physics behind the mechanism of the two-photon optical pumping of the isomer is considered. It is shown that, irrespective of the pumping scheme, a dominant contribution comes, in accord with what was proven earlier for the 3.5-eV isomer, from the resonance 8 s-7 s transition. Details of an optimum experimental scheme are discussed. It is shown that, after isomer excitation, the atom involved remains with a high probability in an excited state at an energy of about 0.5 eV rather than in the ground state, the required energy of the two photons being equal to the energy of the nuclear level plus the energy of the lowest 7 s state of the atom. The estimated pumping time is about 1.5 s in the case where the field strength of each laser is 1 V/cm.

Excitation Mechanisms in Moderate-Energy Li+-He Collisions

NASA Astrophysics Data System (ADS)

Kita, Shigetomo; Itaya, Jun; Sawatari, Yugo; Tabata, Tadanobu; Hayashi, Takeo; Shimakura, Noriyuki; Koseki, Shiro

2018-02-01

Excitation mechanisms in Li+-He collisions were studied at laboratory collision energies of 350 ≤ Elab ≤ 2000 eV by measuring double differential cross sections (DCSs) σ(Θ)k over a wide range of center-of-mass scattering angles, 2.5 ≤ Θ ≤ 175°. At Elab ≥ 500 eV, two-electron (2e) excitations were observed as well as one-electron (1e) excitations. At the higher collision energies, excitation probabilities P(Θ)k for the 1e and 2e excitations have characteristic angular dependences, i.e., at Elab = 1500 and 2000 eV, P(Θ)1e for the 1e excitations has double maxima around Θ = 20 and 120° and P(Θ)2e for the 2e excitations has a broad maximum around Θ = 60°. As a first analysis of the experimental data, P(Θ)k, σ(Θ)k, and the integral cross sections Sk(Elab) were calculated by assuming excitations from the 11Σ state into the 11Π and 11Δ states through rotational couplings using the model potentials and couplings. As the next step, ab initio potential energies for the ground and excited states were calculated by a multiconfiguration self-consistent field (MCSCF) method, and then the electronic transitions among the seven states through the radial and rotational couplings were calculated using the theoretical potentials and couplings. Autoionizations from the 2e-excited He**(2s2 and 2p2) atoms were also simulated at Elab = 750-1500 eV and small laboratory angles of θ ≤ 25° by using the MCSCF potentials. The excitation mechanisms were reasonably well understood through these analyses.

Two-Photon Excitation of Launched Cold Atoms in Flight

NASA Astrophysics Data System (ADS)

Goodsell, Anne; Gonzalez, Rene; Alejandro, Eduardo; Erwin, Emma

2017-04-01

We demonstrate two-photon bi-chromatic excitation of cold rubidium atoms in flight, using the pathway 5S1 / 2 -> 5P3 / 2 -> 5D5 / 2 with two resonant photons. In our experiment, atoms are laser-cooled in a magneto-optical trap and launched upward in discrete clouds with a controllable vertical speed of 7.1 +/-0.6 m/s and a velocity spread that is less than 10% of the launch speed. Outside the cooling beams, as high as 14 mm above the original center of the trap, the launched cold atoms are illuminated simultaneously by spatially-localized horizontal excitation beams at 780 nm (5S1 / 2 -> 5P3 / 2) and 776 nm (5P3 / 2 -> 5D5 / 2). We monitor transmission of the 780-nm beam over a range of intensities of 780-nm and 776-nm light. As the center of the moving cloud passes the excitation beams, we observe as much as 97.9 +/-1.2% transmission when the rate of two-photon absorption is high and the 5S1 / 2 and 5P3 / 2 states are depopulated, compared to 87.6 +/-0.9% transmission if only the 780-nm beam is present. This demonstrates two-photon excitation of a launched cold-atom source with controllable launch velocity and narrow velocity spread, as a foundation for three-photon excitation to Rydberg states. Research supported by Middlebury College Bicentennial Fund, Palen Fund, and Gladstone Award.

One Photon Can Simultaneously Excite Two or More Atoms.

PubMed

Garziano, Luigi; Macrì, Vincenzo; Stassi, Roberto; Di Stefano, Omar; Nori, Franco; Savasta, Salvatore

2016-07-22

We consider two separate atoms interacting with a single-mode optical or microwave resonator. When the frequency of the resonator field is twice the atomic transition frequency, we show that there exists a resonant coupling between one photon and two atoms, via intermediate virtual states connected by counterrotating processes. If the resonator is prepared in its one-photon state, the photon can be jointly absorbed by the two atoms in their ground state which will both reach their excited state with a probability close to one. Like ordinary quantum Rabi oscillations, this process is coherent and reversible, so that two atoms in their excited state will undergo a downward transition jointly emitting a single cavity photon. This joint absorption and emission process can also occur with three atoms. The parameters used to investigate this process correspond to experimentally demonstrated values in circuit quantum electrodynamics systems.

Excitation energies from Görling-Levy perturbation theory along the range-separated adiabatic connection

NASA Astrophysics Data System (ADS)

Rebolini, Elisa; Teale, Andrew M.; Helgaker, Trygve; Savin, Andreas; Toulouse, Julien

2018-06-01

A Görling-Levy (GL)-based perturbation theory along the range-separated adiabatic connection is assessed for the calculation of electronic excitation energies. In comparison with the Rayleigh-Schrödinger (RS)-based perturbation theory this GL-based perturbation theory keeps the ground-state density constant at each order and thus gives the correct ionisation energy at each order. Excitation energies up to first order in the perturbation have been calculated numerically for the helium and beryllium atoms and the hydrogen molecule without introducing any density-functional approximations. In comparison with the RS-based perturbation theory, the present GL-based perturbation theory gives much more accurate excitation energies for Rydberg states but similar excitation energies for valence states.

Rydberg interaction induced enhanced excitation in thermal atomic vapor.

PubMed

Kara, Dushmanta; Bhowmick, Arup; Mohapatra, Ashok K

2018-03-27

We present the experimental demonstration of interaction induced enhancement in Rydberg excitation or Rydberg anti-blockade in thermal atomic vapor. We have used optical heterodyne detection technique to measure Rydberg population due to two-photon excitation to the Rydberg state. The anti-blockade peak which doesn't satisfy the two-photon resonant condition is observed along with the usual two-photon resonant peak which can't be explained using the model with non-interacting three-level atomic system. A model involving two interacting atoms is formulated for thermal atomic vapor using the dressed states of three-level atomic system to explain the experimental observations. A non-linear dependence of vapor density is observed for the anti-blockade peak which also increases with increase in principal quantum number of the Rydberg state. A good agreement is found between the experimental observations and the proposed interacting model. Our result implies possible applications towards quantum logic gates using Rydberg anti-blockade in thermal atomic vapor.

Excitation of the {sup 229m}Th nuclear isomer via resonance conversion in ionized atoms

DOE Office of Scientific and Technical Information (OSTI.GOV)

Karpeshin, F. F., E-mail: fkarpeshin@gmail.com; Trzhaskovskaya, M. B.

2015-09-15

Pressing problems concerning the optical pumping of the 7.6-eV {sup 229m}Th nuclear isomer, which is a candidate for a new nuclear optical reference point for frequencies, are examined. Physics behind the mechanism of the two-photon optical pumping of the isomer is considered. It is shown that, irrespective of the pumping scheme, a dominant contribution comes, in accord with what was proven earlier for the 3.5-eV isomer, from the resonance 8s–7s transition. Details of an optimum experimental scheme are discussed. It is shown that, after isomer excitation, the atom involved remains with a high probability in an excited state at anmore » energy of about 0.5 eV rather than in the ground state, the required energy of the two photons being equal to the energy of the nuclear level plus the energy of the lowest 7s state of the atom. The estimated pumping time is about 1.5 s in the case where the field strength of each laser is 1 V/cm.« less

Energy transfer of highly vibrationally excited phenanthrene and diphenylacetylene.

PubMed

Hsu, Hsu Chen; Tsai, Ming-Tsang; Dyakov, Yuri; Ni, Chi-Kung

2011-05-14

The energy transfer between Kr atoms and highly vibrationally excited, rotationally cold phenanthrene and diphenylacetylene in the triplet state was investigated using crossed-beam/time-of-flight mass spectrometer/time-sliced velocity map ion imaging techniques. Compared to the energy transfer between naphthalene and Kr, energy transfer between phenanthrene and Kr shows a larger cross-section for vibrational to translational (V → T) energy transfer, a smaller cross-section for translational to vibrational and rotational (T → VR) energy transfer, and more energy transferred from vibration to translation. These differences are further enlarged in the comparison between naphthalene and diphenylacetylene. In addition, less complex formation and significant increases in the large V → T energy transfer probabilities, termed supercollisions in diphenylacetylene and Kr collisions were observed. The differences in the energy transfer between these highly vibrationally excited molecules are attributed to the low-frequency vibrational modes, especially those vibrations with rotation-like wide-angle motions.

Excitation of atoms and ions in plasmas by ultra-short electromagnetic pulses

NASA Astrophysics Data System (ADS)

Astapenko, V. A.; Sakhno, S. V.; Svita, S. Yu; Lisitsa, V. S.

2017-02-01

The problem of atoms and ions diagnostics in rarefied and dense plasmas by ultrashort laser pulses (USP) is under consideration. The application of USP provides: 1) excitation from ground states due to their carrier frequency high enough, 2) penetration into optically dense media due to short pulses duration. The excitation from ground atomic states increases sharply populations of excited atomic states in contrast with standard laser induced fluorescence spectroscopy based on radiative transitions between excited atomic states. New broadening parameter in radiation absorption, namely inverse pulse duration time 1/τ appears in addition to standard line-shape width in the profile G(ω). The Lyman-beta absorption spectra for USP are calculated for Holtsmark static broadening mechanism. Excitation of highly charged H-like ions in hot plasmas is described by both Gaussian shapes for Doppler broadening and pulse spectrum resulting in analytical absorption line-shape. USP penetration into optically thick media and corresponding excitation probability are calculated. It is shown a great effect of USP duration on excitation probabilities in optically thick media. The typical situations for plasma diagnostics by USP are discussed in details.

An accurate full-dimensional potential energy surface for H-Au(111): Importance of nonadiabatic electronic excitation in energy transfer and adsorption.

PubMed

Janke, Svenja M; Auerbach, Daniel J; Wodtke, Alec M; Kandratsenka, Alexander

2015-09-28

We have constructed a potential energy surface (PES) for H-atoms interacting with fcc Au(111) based on fitting the analytic form of the energy from Effective Medium Theory (EMT) to ab initio energy values calculated with density functional theory. The fit used input from configurations of the H-Au system with Au atoms at their lattice positions as well as configurations with the Au atoms displaced from their lattice positions. It reproduces the energy, in full dimension, not only for the configurations used as input but also for a large number of additional configurations derived from ab initio molecular dynamics (AIMD) trajectories at finite temperature. Adiabatic molecular dynamics simulations on this PES reproduce the energy loss behavior of AIMD. EMT also provides expressions for the embedding electron density, which enabled us to develop a self-consistent approach to simulate nonadiabatic electron-hole pair excitation and their effect on the motion of the incident H-atoms. For H atoms with an energy of 2.7 eV colliding with Au, electron-hole pair excitation is by far the most important energy loss pathway, giving an average energy loss ≈3 times that of the adiabatic case. This increased energy loss enhances the probability of the H-atom remaining on or in the Au slab by a factor of 2. The most likely outcome for H-atoms that are not scattered also depends prodigiously on the energy transfer mechanism; for the nonadiabatic case, more than 50% of the H-atoms which do not scatter are adsorbed on the surface, while for the adiabatic case more than 50% pass entirely through the 4 layer simulation slab.

Energy-transfer processes in neon-hydrogen mixtures excited by electron beams

DOE Office of Scientific and Technical Information (OSTI.GOV)

Morozov, A.; Kruecken, R.; Ulrich, A.

2005-12-15

Energy- and charge-transfer processes in neon-hydrogen mixtures (500-1400 hPa neon and 0.001-3 hPa hydrogen partial pressures) excited by a pulsed low-energy ({approx}10 keV) electron beam were investigated using time-resolved spectroscopy. Time spectra of the hydrogen Lyman-{alpha} line, neon excimer emission (second continuum), and neon atomic lines (3p-3s transitions) were recorded. The time-integrated intensity of the Lyman-{alpha} emission was measured for the same range of gas mixtures. It is shown that direct energy transfer from Ne{sub 2}* excimers and neon atoms in the four lowest excited states as well as recombination of H{sub 3}{sup +} ions are the main channels populatingmore » atomic hydrogen in the n=2 state. A rate constant of (4.2{+-}1.4)x10{sup -11} cm{sup 3} s{sup -1} was obtained for the charge transfer from Ne{sub 2}{sup +} ions to molecular hydrogen. A lower limit for the depopulation rate constant of Ne{sub 2}* excimers by molecular hydrogen (combination of energy transfer and ionization) was found to be 1.0x10{sup -10} cm{sup 3} s{sup -1}.« less

Effect of Electronic Excitation on Hydrogen Atom Transfer (Tautomerization) Reactions for the DNA Base Adenine

NASA Technical Reports Server (NTRS)

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

2002-01-01

Geometrical structures and energetic properties for four different tautomers of adenine are calculated in this study, using multi-configurational wave functions. Both the ground and the lowest single excited state potential energy surface are studied. The energetic order of the tautomers on the ground state potential surface is 9H less than 7H less than 3H less than 1H, while on the excited state surface this order is found to be different: 3H less than 1H less than 9H less than 7H. Minimum energy reaction paths are obtained for hydrogen atom transfer (9 yields 3 tautomerization) reactions in the ground and the lowest excited electronic state. It is found that the barrier heights and the shapes of the reaction paths are different for the ground and the excited electronic state, suggesting that the probability of such tautomerization reaction is higher on the excited state potential energy surface. The barrier for this reaction in the excited state may become very low in the presence of water or other polar solvent molecules, and therefore such tautomerization reaction may play an important role in the solution phase photochemistry of adenine.

Reaction and electronic excitation in crossed-beams collisions of low-energy O(3P) atoms with H2O and CO2

NASA Technical Reports Server (NTRS)

Orient, O. J.; Chutjian, A.; Murad, E.

1990-01-01

Collisions of low-energy (5-20 eV), ground-state oxygen atoms with H2O and CO2 in a crossed-beams geometry lead to chemical reaction in the case of H2O to produce OH (A2Sigma+ - X2Pi) emissions; and to inelastic electronic excitation in the case of CO2 to produce CO2 flame bands. Species identifications are made through known wavelengths and emission intensities in the range 300-400 nm. The measured difference in threshold energies for the two processes confirm the channels involved. These are the first measurements in this energy range of optical emissions through collisions of fast neutral species.

Near-field excitation exchange between motionless point atoms located near the conductive surface

NASA Astrophysics Data System (ADS)

Kuraptsev, Aleksei S.; Sokolov, Igor M.

2018-04-01

On the basis of quantum microscopic approach we study the excitation dynamics of two motionless point atoms located near the perfectly conducting mirror. We have analyzed the spontaneous decay rate of individual atoms near the mirror as well as the strength of dipole-dipole interaction between different atoms. It is shown that the spontaneous decay rate of an excited atom significantly depends on the distance from this atom to the mirror. In the case when the interatomic separation is less or comparable with the wavelength of resonant radiation, the spontaneous decay dynamics of an excited atom is described by multi-exponential law. It depends both the interatomic separation and the spatial orientation of diatomic quasimolecule.

Theoretical Study of Energy Levels and Transition Probabilities of Boron Atom

NASA Astrophysics Data System (ADS)

Tian Yi, Zhang; Neng Wu, Zheng

2009-08-01

Full Text PDF Though the electrons configuration for boron atom is simple and boron atom has long been of interest for many researchers, the theoretical studies for properties of BI are not systematic, there are only few results reported on energy levels of high excited states of boron, and transition measurements are generally restricted to transitions involving ground states and low excited states without considering fine structure effects, provided only multiplet results, values for transitions between high excited states are seldom performed. In this article, by using the scheme of the weakest bound electron potential model theory calculations for energy levels of five series are performed and with the same method we give the transition probabilities between excited states with considering fine structure effects. The comprehensive set of calculations attempted in this paper could be of some value to workers in the field because of the lack of published calculations for the BI systems. The perturbations coming from foreign perturbers are taken into account in studying the energy levels. Good agreement between our results and the accepted values taken from NIST has been obtained. We also reported some values of energy levels and transition probabilities not existing on the NIST data bases.

The interaction of excited He, Ar and Ne metastable atoms with the CF2Cl2 molecule

NASA Astrophysics Data System (ADS)

Cherid, M.; Ben Arfa, M.; Driss Khodja, M.

2004-02-01

We studied Penning ionization of the CF2Cl2 molecule by neon and helium metastable atoms. In the case of the neon ionizing particle, we measured the electron kinetic energy as well as mass spectra; for helium metastable atoms, only the mass spectrum was recorded. We, therefore, obtained the branching ratios for the heavy charged particles produced in both interactions. In this report we will discuss the mechanism involved in the production of metastable halogen atoms in the dielectric barrier discharge further to the use of rare gases/CF2Cl2 mixtures. We show that this process needs a two-stage reaction. Ground state free halogen atoms are formed over the first stage by Penning ionization, charge transfer, dissociate excitation and ionization. Therefore, metastable halogen atoms can be produced by excitation transfer process in the second stage through interaction with metastable rare gas atoms. This paper is dedicated to Professor F M E Tuffin on the occasion of his retirement.

Laser techniques for spectroscopy of core-excited atomic levels

NASA Technical Reports Server (NTRS)

Harris, S. E.; Young, J. F.; Falcone, R. W.; Rothenberg, J. E.; Willison, J. R.

1982-01-01

We discuss three techniques which allow the use of tunable lasers for high resolution and picosecond time scale spectroscopy of core-excited atomic levels. These are: anti-Stokes absorption spectroscopy, laser induced emission from metastable levels, and laser designation of selected core-excited levels.

Liquid-Arc/Spark-Excitation Atomic-Emission Spectroscopy

NASA Technical Reports Server (NTRS)

Schlagen, Kenneth J.

1992-01-01

Constituents of solutions identified in situ. Liquid-arc/spark-excitation atomic-emission spectroscopy (LAES) is experimental variant of atomic-emission spectroscopy in which electric arc or spark established in liquid and spectrum of light from arc or spark analyzed to identify chemical elements in liquid. Observations encourage development of LAES equipment for online monitoring of process streams in such industries as metal plating, electronics, and steel, and for online monitoring of streams affecting environment.

Optical oscillator strengths of the valence-shell excitations of atoms and molecules determined by the dipole ( γ,γ) method

NASA Astrophysics Data System (ADS)

Xu, Long-Quan; Liu, Ya-Wei; Xu, Xin; Ni, Dong-Dong; Yang, Ke; Zhu, Lin-Fan

2017-07-01

The dipole (γ,γ) method, which is the inelastic X-ray scattering operated at a negligibly small momentum transfer, has been developed to determine the absolute optical oscillator strengths of the valence-shell excitations of atoms and molecules. This new method is free from the line saturation effect, and its Bethe-Born conversion factor varies much more slowly with the excitation energy than that of the dipole (e, e) method. Thus the dipole (γ,γ) method provides a reliable approach to obtain the benchmark optical oscillator strengths of the valence-shell excitations for gaseous atoms and molecules. In this paper, we give a review of the dipole (γ,γ) method and some recent measurements of absolute optical oscillator strengths of gaseous atoms and molecules. Contribution to the Topical Issue "Atomic and Molecular Data and their Applications", edited by Gordon W.F. Drake, Jung-Sik Yoon, Daiji Kato, Grzegorz Karwasz.

Kinetic-Energy Distribution of D(2p) Atoms from Analysis of the D Lyman-Alpha Line Profile

NASA Technical Reports Server (NTRS)

Ciocca, M.; Ajello, Joseph M.; Liu, Xianming; Maki, Justin

1997-01-01

The kinetic-energy distribution of D(2p) atoms resulting from electron-impact dissociation of D2 has been measured. A high-resolution vacuum ultraviolet spectrometer was employed for the first measurement of the D Lyman-alpha (D L(alpha)) emission line profiles at 20- and 100-eV excitation energies. Analysis of the deconvoluted line profile of D L(alpha) at 100 eV reveals the existence of a narrow line central peak of 29+/-2 mA full width at half maximum and a broad pedestal wing structure about 190 mA wide. The wings of the line can be used to determine the fast atom distribution. The wings of D L(alpha) arise from dissociative excitation of a series of doubly excited states that cross the Franck-Condon region between 23 and 40 eV. The fast atom distribution at 100-eV electron impact energy spans the energy range from 1 to 10 eV with a peak value near 6 eV. Slow D(2p) atoms characterized by a distribution function with peak energy near 100 meV produce the central peak profile, which is nearly independent of the impact energy. The deconvoluted line profiles of the central peak at 20 eV for dissociative excitation of D2 and H2 are fitted with an analytical function for use in calibration of space flight instrumentation equipped with a D/H absorption cell. The kinetic-energy and line profile results are compared to similar measurements for H2. The absolute cross sections for the line center (slow atoms) and wings (fast atoms) and total emission line profile were measured from threshold to 400 eV. Analytical model coefficients are given for the energy dependence of the measured slow atom cross section.

Electron scattering by laser-excited barium atoms

NASA Technical Reports Server (NTRS)

Register, D. F.; Trajmar, S.; Jensen, S. W.; Poe, R. T.

1978-01-01

Inelastic and superelastic scattering of 30- and 100-eV electrons by laser-excited 6s 6p 1P and subsequent cascade-populated 6s 6p 3P, 6s 5d 1D, and 6s 5d 3D Ba atoms have been observed. Absolute differential cross sections for the singlet and relative scattering intensities for the triplet species have been determined in the 5 to 20 deg angular region. Under the present conditions excitations dominate over deexcitations.

Two photon excitation of atomic oxygen

NASA Technical Reports Server (NTRS)

Pindzola, M. S.

1977-01-01

A standard perturbation expansion in the atom-radiation field interaction is used to calculate the two photon excitation cross section for 1s(2) 2s(2) 2p(4) p3 to 1s(2) 2s(2) 2p(3) (s4) 3p p3 transition in atomic oxygen. The summation over bound and continuum intermediate states is handled by solving the equivalent inhomogeneous differential equation. Exact summation results differ by a factor of 2 from a rough estimate obtained by limiting the intermediate state summation to one bound state. Higher order electron correlation effects are also examined.

Localization of atomic excitation beyond the diffraction limit using electromagnetically induced transparency

NASA Astrophysics Data System (ADS)

Miles, J. A.; Das, Diptaranjan; Simmons, Z. J.; Yavuz, D. D.

2015-09-01

We experimentally demonstrate the localization of excitation between hyperfine ground states of 87Rb atoms to as small as λ /13 -wide spatial regions. We use ultracold atoms trapped in a dipole trap and utilize electromagnetically induced transparency (EIT) for the atomic excitation. The localization is achieved by combining a spatially varying coupling laser (standing wave) with the intensity dependence of EIT. The excitation is fast (150 ns laser pulses) and the dark-state fidelity can be made higher than 94% throughout the standing wave. Because the width of the localized regions is much smaller than the wavelength of the driving light, traditional optical imaging techniques cannot resolve the localized features. Therefore, to measure the excitation profile, we use an autocorrelation-like method where we perform two EIT sequences separated by a time delay, during which we move the standing wave.

σ-SCF: A direct energy-targeting method to mean-field excited states.

PubMed

Ye, Hong-Zhou; Welborn, Matthew; Ricke, Nathan D; Van Voorhis, Troy

2017-12-07

The mean-field solutions of electronic excited states are much less accessible than ground state (e.g., Hartree-Fock) solutions. Energy-based optimization methods for excited states, like Δ-SCF (self-consistent field), tend to fall into the lowest solution consistent with a given symmetry-a problem known as "variational collapse." In this work, we combine the ideas of direct energy-targeting and variance-based optimization in order to describe excited states at the mean-field level. The resulting method, σ-SCF, has several advantages. First, it allows one to target any desired excited state by specifying a single parameter: a guess of the energy of that state. It can therefore, in principle, find all excited states. Second, it avoids variational collapse by using a variance-based, unconstrained local minimization. As a consequence, all states-ground or excited-are treated on an equal footing. Third, it provides an alternate approach to locate Δ-SCF solutions that are otherwise hardly accessible by the usual non-aufbau configuration initial guess. We present results for this new method for small atoms (He, Be) and molecules (H 2 , HF). We find that σ-SCF is very effective at locating excited states, including individual, high energy excitations within a dense manifold of excited states. Like all single determinant methods, σ-SCF shows prominent spin-symmetry breaking for open shell states and our results suggest that this method could be further improved with spin projection.

Testing time-dependent density functional theory with depopulated molecular orbitals for predicting electronic excitation energies of valence, Rydberg, and charge-transfer states and potential energies near a conical intersection

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Shaohong L.; Truhlar, Donald G., E-mail: truhlar@umn.edu

2014-09-14

Kohn-Sham (KS) time-dependent density functional theory (TDDFT) with most exchange-correlation functionals is well known to systematically underestimate the excitation energies of Rydberg and charge-transfer excited states of atomic and molecular systems. To improve the description of Rydberg states within the KS TDDFT framework, Gaiduk et al. [Phys. Rev. Lett. 108, 253005 (2012)] proposed a scheme that may be called HOMO depopulation. In this study, we tested this scheme on an extensive dataset of valence and Rydberg excitation energies of various atoms, ions, and molecules. It is also tested on a charge-transfer excitation of NH{sub 3}-F{sub 2} and on the potentialmore » energy curves of NH{sub 3} near a conical intersection. We found that the method can indeed significantly improve the accuracy of predicted Rydberg excitation energies while preserving reasonable accuracy for valence excitation energies. However, it does not appear to improve the description of charge-transfer excitations that are severely underestimated by standard KS TDDFT with conventional exchange-correlation functionals, nor does it perform appreciably better than standard TDDFT for the calculation of potential energy surfaces.« less

The formation of excited atoms during charge exchange between hydrogen ions and alkali atoms. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Nieman, R. A.

1971-01-01

The charge exchange cross sections for protons and various alkali atoms are calculated using the classical approximation of Gryzinski. It is assumed that the hydrogen atoms resulting from charge exchange exist in all possible excited states. Charge transfer collisions between protons and potassium as well as protons and sodium atoms are studied. The energy range investigated is between 4 and 30 keV. The theoretical calculations of the capture cross section and the cross section for the creation of metastable 2S hydrogen are compared to experimental values. Good quantitative agreement is found for the capture cross section but only qualitative agreement for the metastable cross section. Analysis of the Lyman alpha window in molecular oxygen suggests that measured values of the metastable cross section may be in error. Thick alkali target data are also presented. This allows the determination of the total electron loss cross section. Finally, some work was done with H2(+).

σ -SCF: A Direct Energy-targeting Method To Mean-field Excited States

NASA Astrophysics Data System (ADS)

Ye, Hongzhou; Welborn, Matthew; Ricke, Nathan; van Voorhis, Troy

The mean-field solutions of electronic excited states are much less accessible than ground state (e.g. Hartree-Fock) solutions. Energy-based optimization methods for excited states, like Δ-SCF, tend to fall into the lowest solution consistent with a given symmetry - a problem known as ``variational collapse''. In this work, we combine the ideas of direct energy-targeting and variance-based optimization in order to describe excited states at the mean-field level. The resulting method, σ-SCF, has several advantages. First, it allows one to target any desired excited state by specifying a single parameter: a guess of the energy of that state. It can therefore, in principle, find all excited states. Second, it avoids variational collapse by using a variance-based, unconstrained local minimization. As a consequence, all states - ground or excited - are treated on an equal footing. Third, it provides an alternate approach to locate Δ-SCF solutions that are otherwise hardly accessible by the usual non-aufbau configuration initial guess. We present results for this new method for small atoms (He, Be) and molecules (H2, HF). This work was funded by a Grant from NSF (CHE-1464804).

Chapter 6 Quantum Mechanical Methods for Loss-Excitation and Loss-Ionization in Fast Ion-Atom Collisions

NASA Astrophysics Data System (ADS)

Belkic, Dzevad

Inelastic collisions between bare nuclei and hydrogen-like atomic systems are characterized by three main channels: electron capture, excitation, and ionization. Capture dominates at lower energies, whereas excitation and ionization prevail at higher impact energies. At intermediate energies and in the region of resonant scattering near the Massey peak, all three channels become competitive. For dressed or clothed nuclei possessing electrons, such as hydrogen-like ions, several additional channels open up, including electron loss (projectile ionization or stripping). The most important aspect of electron loss is the competition between one- and two-electron processes. Here, in a typical one-electron process, the projectile emits an electron, whereas the target final and initial states are the same. A prototype of double-electron transitions in loss processes is projectile ionization accompanied with an alteration of the target state. In such a two-electron process, the target could be excited or ionized. The relative importance of these loss channels with single- and double-electron transitions involving collisions of dressed projectiles with atomic systems is also strongly dependent on the value of the impact energy. Moreover, impact energies determine which theoretical method is likely to be more appropriate to use for predictions of cross sections. At low energies, an expansion of total scattering wave functions in terms of molecular orbitals is adequate. This is because the projectile spends considerable time in the vicinity of the target, and as a result, a compound system comprised of the projectile and the target can be formed in a metastable molecular state which is prone to decay. At high energies, a perturbation series expansion is more appropriate in terms of powers of interaction potentials. In the intermediate energy region, atomic orbitals are often used with success while expanding the total scattering wave functions. The present work is focused on

Excitation of the hydrogen atom by fast-electron impact in the presence of a laser field

NASA Astrophysics Data System (ADS)

Bhattacharya, Manabesh; Sinha, C.; Sil, N. C.

1991-08-01

An approach has been developed to study the excitation of a ground-state H atom to the n=2 level under the simultaneous action of fast-electron impact and a monochromatic, linearly polarized, homogeneous laser beam. The laser frequency is assumed to be low (soft-photon limit) so that a stationary-state perturbation theory can be applied as is done in the adiabatic theory. An elegant method has been developed in the present work to construct the dressed excited-state wave functions of the H atom using first-order perturbation theory in the parabolic coordinate representation. By virtue of this method, the problem arising due to the degeneracy of the excited states of the H atom has been successfully overcome. The main advantage of the present approach is that the dressed wave function has been obtained in terms of a finite number of Laguerre polynomials instead of an infinite summation occurring in the usual perturbative treatment. The amplitude for direct excitation (without exchange) has been obtained in closed form. Numerical results for differential cross sections are presented for individual excitations to different Stark manifolds as well as for excitations to the n=2 level at high energies (100 and 200 eV) and for field directions both parallel and perpendicular to the incident electron momentum. Extension to a higher order of perturbation is also possible in the present approach for the construction of the dressed states, and the electron-exchange effect can also be taken into account without any further approximation.

Limit on Excitation and Stabilization of Atoms in Intense Optical Laser Fields.

PubMed

Zimmermann, H; Meise, S; Khujakulov, A; Magaña, A; Saenz, A; Eichmann, U

2018-03-23

Atomic excitation in strong optical laser fields has been found to take place even at intensities exceeding saturation. The concomitant acceleration of the atom in the focused laser field has been considered a strong link to, if not proof of, the existence of the so-called Kramers-Henneberger (KH) atom, a bound atomic system in an intense laser field. Recent findings have moved the importance of the KH atom from being purely of theoretical interest toward real world applications; for instance, in the context of laser filamentation. Considering this increasing importance, we explore the limits of strong-field excitation in optical fields, which are basically imposed by ionization through the spatial field envelope and the field propagation.

Relative Energy Shift of a Two-Level Atom in a Cylindrical Spacetime

NASA Astrophysics Data System (ADS)

Zhang, Jia-Lin

2012-11-01

We investigate the evolution dynamics of a two-level atom system interacting with the massless scalar field in a Cylindrical spacetime. We find that both the energy shifts of ground state and excited state can be separated into two parts due to the vacuum fluctuations. One is the corresponding energy shift for a rest atom in four-dimensional Minkowski space without spatial compactification, the other is just the modification of the spatial compactified periodic length. It will reveal that the influence of the presence of one spatial compactified dimension can not be neglected in Lamb shift as the relative energy level shift of an atom.

σ-SCF: A direct energy-targeting method to mean-field excited states

NASA Astrophysics Data System (ADS)

Ye, Hong-Zhou; Welborn, Matthew; Ricke, Nathan D.; Van Voorhis, Troy

2017-12-01

The mean-field solutions of electronic excited states are much less accessible than ground state (e.g., Hartree-Fock) solutions. Energy-based optimization methods for excited states, like Δ-SCF (self-consistent field), tend to fall into the lowest solution consistent with a given symmetry—a problem known as "variational collapse." In this work, we combine the ideas of direct energy-targeting and variance-based optimization in order to describe excited states at the mean-field level. The resulting method, σ-SCF, has several advantages. First, it allows one to target any desired excited state by specifying a single parameter: a guess of the energy of that state. It can therefore, in principle, find all excited states. Second, it avoids variational collapse by using a variance-based, unconstrained local minimization. As a consequence, all states—ground or excited—are treated on an equal footing. Third, it provides an alternate approach to locate Δ-SCF solutions that are otherwise hardly accessible by the usual non-aufbau configuration initial guess. We present results for this new method for small atoms (He, Be) and molecules (H2, HF). We find that σ-SCF is very effective at locating excited states, including individual, high energy excitations within a dense manifold of excited states. Like all single determinant methods, σ-SCF shows prominent spin-symmetry breaking for open shell states and our results suggest that this method could be further improved with spin projection.

Final excitation energy of fission fragments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schmidt, Karl-Heinz; Jurado, Beatriz

We study how the excitation energy of the fully accelerated fission fragments is built up. It is stressed that only the intrinsic excitation energy available before scission can be exchanged between the fission fragments to achieve thermal equilibrium. This is in contradiction with most models used to calculate prompt neutron emission, where it is assumed that the total excitation energy of the final fragments is shared between the fragments by the condition of equal temperatures. We also study the intrinsic excitation-energy partition in statistical equilibrium for different level-density descriptions as a function of the total intrinsic excitation energy of themore » fissioning system. Excitation energies are found to be strongly enhanced in the heavy fragment, if the level density follows a constant-temperature behavior at low energies, e.g., in the composed Gilbert-Cameron description.« less

Noise squeezing of fields that bichromatically excite atoms in a cavity.

PubMed

Li, Lingchao; Hu, Xiangming; Rao, Shi; Xu, Jun

2016-11-14

It is well known that bichromatic excitation on one common transition can tune the emission or absorption spectra of atoms due to the modulation frequency dependent non-linearities. However little attention has been focused on the quantum dynamics of fields under bichromatic excitation. Here we present dissipative effects on noise correlations of fields in bichromatic interactions with atoms in cavities. We first consider an ensemble of two-level atoms that interacts with the two cavity fields of different frequencies and considerable amplitudes. By transferring the atom-field nonlinearities to the dressed atoms we separate out the dissipative interactions of Bogoliubov modes with the dressed atoms. The Bogoliubov mode dissipation establishes stable two-photon processes of two involved fields and therefore leads to two-mode squeezing. As a generalization, we then consider an ensemble of three-level Λ atoms for cascade bichromatic interactions. We extract the Bogoliubov-like four-mode interactions, which establish a quadrilateral of the two-photon processes of four involved fields and thus result in four-mode squeezing.

Energetic ion, atom, and molecule reactions and excitation in low-current H2 discharges: H(alpha) Doppler profiles.

PubMed

Petrović, Z Lj; Phelps, A V

2009-12-01

Absolute spectral emissivities for Doppler broadened H(alpha) profiles are measured and compared with predictions of energetic hydrogen ion, atom, and molecule behavior in low-current electrical discharges in H2 at very high electric field E to gas density N ratios E/N and low values of Nd , where d is the parallel-plate electrode separation. These observations reflect the energy and angular distributions for the excited atoms and quantitatively test features of multiple-scattering kinetic models in weakly ionized hydrogen in the presence of an electric field that are not tested by the spatial distributions of H(alpha) emission. Absolute spectral intensities agree well with predictions. Asymmetries in Doppler profiles observed parallel to the electric field at 4excitation by fast H atoms directed toward the cathode and diffusely reflected from the cathode. (1 Td=10(-21) V m(2)) The effects of reflection of hydrogen particles and of changes with cathode material are modeled accurately without adjustable parameters. Maximum measured wavelength shifts result from acceleration of H+ ions and charge transfer to fast H atoms. The Doppler profiles are consistent with models of reactions among H+, H2+, H3 , H, and H2 leading to fast H atoms and then fast excited H(n=3) atoms.

Investigation of polar and stereoelectronic effects on pure excited-state hydrogen atom abstractions from phenols and alkylbenzenes.

PubMed

Pischel, Uwe; Patra, Digambara; Koner, Apurba L; Nau, Werner M

2006-01-01

The fluorescence quenching of singlet-excited 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO) by 22 phenols and 12 alkylbenzenes has been investigated. Quenching rate constants in acetonitrile are in the range of 10(8)-10(9) M(-1)s(-1) for phenols and 10(5)-10(6) M(-1)s(-1) for alkylbenzenes. In contrast to the quenching of triplet-excited benzophenone, no exciplexes are involved, so that a pure hydrogen atom transfer is proposed as quenching mechanism. This is supported by (1) pronounced deuterium isotope effects (kH/kD ca 4-6), which were observed for phenols and alkylbenzenes, and (2) a strongly endergonic thermodynamics for charge transfer processes (electron transfer, exciplex formation). In the case of phenols, linear free energy relationships applied, which led to a reaction constant of rho = -0.40, suggesting a lower electrophilicity of singlet-excited DBO than that of triplet-excited ketones and alkoxyl radicals. The reactivity of singlet-excited DBO exposes statistical, steric, polar and stereoelectronic effects on the hydrogen atom abstraction process in the absence of complications because of competitive exciplex formation.

Relaxation channels of multi-photon excited xenon clusters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Serdobintsev, P. Yu.; Melnikov, A. S.; Department of Physics, St. Petersburg State University, Saint Petersburg 198904

2015-09-21

The relaxation processes of the xenon clusters subjected to multi-photon excitation by laser radiation with quantum energies significantly lower than the thresholds of excitation of atoms and ionization of clusters were studied. Results obtained by means of the photoelectron spectroscopy method showed that desorption processes of excited atoms play a significant role in the decay of two-photon excited xenon clusters. A number of excited states of xenon atoms formed during this process were discovered and identified.

Current status of free radicals and electronically excited metastable species as high energy propellants

NASA Technical Reports Server (NTRS)

Rosen, G.

1973-01-01

A survey is presented of free radicals and electronically excited metastable species as high energy propellants for rocket engines. Nascent or atomic forms of diatomic gases are considered free radicals as well as the highly reactive diatomic triatomic molecules that posess unpaired electrons. Manufacturing and storage problems are described, and a review of current experimental work related to the manufacture of atomic hydrogen propellants is presented.

Excitation of phonons in medium-energy electron diffraction

NASA Astrophysics Data System (ADS)

Alvarez, M. A. Vicente; Ascolani, H.; Zampieri, G.

1996-03-01

The ``elastic'' backscattering of electrons from crystalline surfaces presents two regimes: a low-energy regime, in which the characteristic low-energy electron diffraction (LEED) pattern is observed, and a medium-energy regime, in which the diffraction pattern is similar to those observed in x-ray photoemission diffraction (XPD) and Auger electron diffraction (AED) experiments. We present a model for the electron scattering which, including the vibrational degrees of freedom of the crystal, contains both regimes and explains the passage from one regime to the other. Our model is based on a separation of the electron and atomic motions (adiabatic approximation) and on a cluster-type formulation of the multiple scattering of the electron. The inelastic scattering events (excitation and/or absorption of phonons) are treated as coherent processes and no break of the phase relation between the incident and the exit paths of the electron is assumed. The LEED and the medium-energy electron diffraction regimes appear naturally in this model as the limit cases of completely elastic scattering and of inelastic scattering with excitation and/or absorption of multiple phonons. Intensity patterns calculated with this model are in very good agreement with recent experiments of electron scattering on Cu(001) at low and medium energies. We show that there is a correspondence between the type of intensity pattern and the mean number of phonons excited and/or absorbed during the scattering: a LEED-like pattern is observed when this mean number is less than 2, LEED-like and XPD/AED-like features coexist when this number is 3-4, and a XPD/AED-like pattern is observed when this number is greater than 5-6.

Excited level populations and excitation kinetics of nonequilibrium ionizing argon discharge plasma of atmospheric pressure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Akatsuka, Hiroshi

2009-04-15

Population densities of excited states of argon atoms are theoretically examined for ionizing argon plasma in a state of nonequilibrium under atmospheric pressure from the viewpoint of elementary processes with collisional radiative model. The dependence of excited state populations on the electron and gas temperatures is discussed. Two electron density regimes are found, which are distinguished by the population and depopulation mechanisms for the excited states in problem. When the electron impact excitation frequency for the population or depopulation is lower than the atomic impact one, the electron density of the plasma is considered as low to estimate the populationmore » and depopulation processes. Some remarkable characteristics of population and depopulation mechanisms are found for the low electron density atmospheric plasma, where thermal relaxation by atomic collisions becomes the predominant process within the group of close-energy states in the ionizing plasma of atmospheric pressure, and the excitation temperature is almost the same as the gas temperature. In addition to the collisional relaxation by argon atoms, electron impact excitation from the ground state is also an essential population mechanism. The ratios of population density of the levels pairs, between which exists a large energy gap, include information on the electron collisional kinetics. For high electron density, the effect of atomic collisional relaxation becomes weak. For this case, the excitation mechanism is explained as electron impact ladderlike excitation similar to low-pressure ionizing plasma, since the electron collision becomes the dominant process for the population and depopulation kinetics.« less

Core excitation effects on oscillator strengths for transitions in four electron atomic systems

NASA Astrophysics Data System (ADS)

Chang, T. N.; Luo, Yuxiang

2007-06-01

By including explicitly the electronic configurations with two and three simultaneously excited electronic orbital, we have extended the BSCI (B-spline based configuration interaction) method [1] to estimate directly the effect of inner shell core excitation to oscillator strengths for transitions in four-electron atomic systems. We will present explicitly the change in oscillator strengths due to core excitations, especially for transitions involving doubly excited states and those with very small oscillator strengths. The length and velocity results are typically in agreement better than 1% or less. [1] Tu-nan Chang, in Many-body Theory of Atomic Structure and Photoionization, edited by T. N. Chang (World Scientific, Singapore, 1993), p. 213-47; and T. N. Chang and T. K. Fang, Elsevier Radiation Physics and Chemistry 70, 173-190 (2004).

Energy transfer of highly vibrationally excited naphthalene: collisions with CHF3, CF4, and Kr.

PubMed

Chen Hsu, Hsu; Tsai, Ming-Tsang; Dyakov, Yuri A; Ni, Chi-Kung

2011-08-07

Energy transfer of highly vibrationally excited naphthalene in the triplet state in collisions with CHF(3), CF(4), and Kr was studied using a crossed-beam apparatus along with time-sliced velocity map ion imaging techniques. Highly vibrationally excited naphthalene (2.0 eV vibrational energy) was formed via the rapid intersystem crossing of naphthalene initially excited to the S(2) state by 266 nm photons. The shapes of the collisional energy-transfer probability density functions were measured directly from the scattering results of highly vibrationally excited naphthalene. In comparison to Kr atoms, the energy transfer in collisions between CHF(3) and naphthalene shows more forward scatterings, larger cross section for vibrational to translational (V → T) energy transfer, smaller cross section for translational to vibrational and rotational (T → VR) energy transfer, and more energy transferred from vibration to translation, especially in the range -ΔE(d) = -100 to -800 cm(-1). On the other hand, the difference of energy transfer properties between collisional partners Kr and CF(4) is small. The enhancement of the V → T energy transfer in collisions with CHF(3) is attributed to the large attractive interaction between naphthalene and CHF(3) (1-3 kcal/mol).

Electronic excitation of Na due to low-energy He collisions

NASA Astrophysics Data System (ADS)

Lin, C. Y.; Liebermann, H. P.

2005-05-01

In warm astrophysical environments electron collisions are the primary mechanism for thermalizing the internal energy of ambient atoms and molecules. However, in cool stellar and planetary atmospheres, the electron abundance is extremely low so that thermalization is only possible through collisions of the dominant neutral species, H2, He, and H. Typically, the neutral cross sections are much smaller than those due to electrons, so that the level populations of the atmospheric constituents may display departures from equilibrium. Unfortunately, these cross sections are generally not available for collision energies typical of stellar/planetary environments. In this work, we investigate the electronic excitation of Na due to collisions with He for energies near and just above threshold. The calculations are performed with the quantum-mechanical molecular-orbital close-coupling method utilizing ab initio adiabatic potential curves and nonadiabatic radial and rotational coupling matrix elements obtained from multireference single- and double- excitation configuration interaction approach. State-to-state cross sections and rate coefficients will be presented and compared with other theoretical and experimental data where available.

A New Approach for Sustainable Energy Systems due to the Excitation of Inner-core Electrons on Zinc Atoms Induced by Surface-ion-recombination

NASA Astrophysics Data System (ADS)

Hamasaki, Mitsugi; Obara, Masumi; Yamaguchi, Mitsuomi; Kuwayama, Masahiro; Obara, Kozo

2011-12-01

The crisis of Nuclear power plants due to the March 11, 2011 Tsunami in Japan suggests an increased need for sustainable science and technology in our society. The authors propose a new physical approach with surface-ion-recombination (SIR) due to the inner-core excitation of zinc atom [Ne]3s23p63d104s2 that brings no magnetic moment. Condensed material indicated the energy dependence of X-ray diffraction intensity, in which exists strong diffuse scattering intensities at 10 eV, 90 eV, 100 eV and 230 eV. These energies are strictly corresponding to zinc of electron systems (3s,3p,3d and these combination). Our approach may have the potential of techniques for future nanotechnology, especially for hydrogen storage systems.

V. S. Lebedev and I. L. Beigman, Physics of Highly Excited Atoms and Ions

NASA Astrophysics Data System (ADS)

Mewe, R.

1999-07-01

This book contains a comprehensive description of the basic principles of the theoretical spectroscopy and experimental spectroscopic diagnostics of Rydberg atoms and ions, i.e., atoms in highly excited states with a very large principal quantum number (n≫1). Rydberg atoms are characterized by a number of peculiar physical properties as compared to atoms in the ground or a low excited state. They have a very small ionization potential (∝1/n2), the highly excited electron has a small orbital velocity (∝1/n), the radius (∝n2) is very large, the excited electron has a long orbital period (∝n3), and the radiation lifetime is very long (∝n3-5). At the same time the R. atom is very sensitive to perturbations from external fields in collisions with charged and neutral targets. In recent years, R. atoms have been observed in laboratory and cosmic conditions for n up to ˜1000, which means that the size amounts to about 0.1 mm, ˜106 times that of an atom in the ground state. The scope of this monograph is to familiarize the reader with today's approaches and methods for describing isolated R. atoms and ions, radiative transitions between highly excited states, and photoionization and photorecombination processes. The authors present a number of efficient methods for describing the structure and properties of R. atoms and calculating processes of collisions with neutral and charged particles as well as spectral-line broadening and shift of Rydberg atomic series in gases, cool and hot plasmas in laboratories and in astrophysical sources. Particular attention is paid to a comparison of theoretical results with available experimental data. The book contains 9 chapters. Chapter 1 gives an introduction to the basic properties of R. atoms (ions), Chapter 2 is devoted to an account of general methods describing an isolated Rydberg atom. Chapter 3 is focussed on the recent achievements in calculations of form factors and dipole matrix elements of different types of

Entanglement between a Photonic Time-Bin Qubit and a Collective Atomic Spin Excitation.

PubMed

Farrera, Pau; Heinze, Georg; de Riedmatten, Hugues

2018-03-09

Entanglement between light and matter combines the advantage of long distance transmission of photonic qubits with the storage and processing capabilities of atomic qubits. To distribute photonic states efficiently over long distances several schemes to encode qubits have been investigated-time-bin encoding being particularly promising due to its robustness against decoherence in optical fibers. Here, we demonstrate the generation of entanglement between a photonic time-bin qubit and a single collective atomic spin excitation (spin wave) in a cold atomic ensemble, followed by the mapping of the atomic qubit onto another photonic qubit. A magnetic field that induces a periodic dephasing and rephasing of the atomic excitation ensures the temporal distinguishability of the two time bins and plays a central role in the entanglement generation. To analyze the generated quantum state, we use largely imbalanced Mach-Zehnder interferometers to perform projective measurements in different qubit bases and verify the entanglement by violating a Clauser-Horne-Shimony-Holt Bell inequality.

Entanglement between a Photonic Time-Bin Qubit and a Collective Atomic Spin Excitation

NASA Astrophysics Data System (ADS)

Farrera, Pau; Heinze, Georg; de Riedmatten, Hugues

2018-03-01

Entanglement between light and matter combines the advantage of long distance transmission of photonic qubits with the storage and processing capabilities of atomic qubits. To distribute photonic states efficiently over long distances several schemes to encode qubits have been investigated—time-bin encoding being particularly promising due to its robustness against decoherence in optical fibers. Here, we demonstrate the generation of entanglement between a photonic time-bin qubit and a single collective atomic spin excitation (spin wave) in a cold atomic ensemble, followed by the mapping of the atomic qubit onto another photonic qubit. A magnetic field that induces a periodic dephasing and rephasing of the atomic excitation ensures the temporal distinguishability of the two time bins and plays a central role in the entanglement generation. To analyze the generated quantum state, we use largely imbalanced Mach-Zehnder interferometers to perform projective measurements in different qubit bases and verify the entanglement by violating a Clauser-Horne-Shimony-Holt Bell inequality.

Energy-resolved coherent diffraction from laser-driven electronic motion in atoms

NASA Astrophysics Data System (ADS)

Shao, Hua-Chieh; Starace, Anthony F.

2017-10-01

We investigate theoretically the use of energy-resolved ultrafast electron diffraction to image laser-driven electronic motion in atoms. A chirped laser pulse is used to transfer the valence electron of the lithium atom from the ground state to the first excited state. During this process, the electronic motion is imaged by 100-fs and 1-fs electron pulses in energy-resolved diffraction measurements. Simulations show that the angle-resolved spectra reveal the time evolution of the energy content and symmetry of the electronic state. The time-dependent diffraction patterns are further interpreted in terms of the momentum transfer. For the case of incident 1-fs electron pulses, the rapid 2 s -2 p quantum beat motion of the target electron is imaged as a time-dependent asymmetric oscillation of the diffraction pattern.

Long-range interactions of hydrogen atoms in excited states. III. n S -1 S interactions for n ≥3

NASA Astrophysics Data System (ADS)

Adhikari, C. M.; Debierre, V.; Jentschura, U. D.

2017-09-01

The long-range interaction of excited neutral atoms has a number of interesting and surprising properties such as the prevalence of long-range oscillatory tails and the emergence of numerically large van der Waals C6 coefficients. Furthermore, the energetically quasidegenerate n P states require special attention and lead to mathematical subtleties. Here we analyze the interaction of excited hydrogen atoms in n S states (3 ≤n ≤12 ) with ground-state hydrogen atoms and find that the C6 coefficients roughly grow with the fourth power of the principal quantum number and can reach values in excess of 240 000 (in atomic units) for states with n =12 . The nonretarded van der Waals result is relevant to the distance range R ≪a0/α , where a0 is the Bohr radius and α is the fine-structure constant. The Casimir-Polder range encompasses the interatomic distance range a0/α ≪R ≪ℏ c /L , where L is the Lamb shift energy. In this range, the contribution of quasidegenerate excited n P states remains nonretarded and competes with the 1 /R2 and 1 /R4 tails of the pole terms, which are generated by lower-lying m P states with 2 ≤m ≤n -1 , due to virtual resonant emission. The dominant pole terms are also analyzed in the Lamb shift range R ≫ℏ c /L . The familiar 1 /R7 asymptotics from the usual Casimir-Polder theory is found to be completely irrelevant for the analysis of excited-state interactions. The calculations are carried out to high precision using computer algebra in order to handle a large number of terms in intermediate steps of the calculation for highly excited states.

[Atomic/ionic fluorescence in microwave plasma torch discharge with excitation of high current and microsecond pulsed hollow cathode lamp: Ca atomic/ionic fluorescence spectrometry].

PubMed

Gong, Zhen-bin; Liang, Feng; Yang, Peng-yuan; Jin, Qin-han; Huang, Ben-li

2002-02-01

A system of atomic and ionic fluorescence spectrometry in microwave plasma torch (MPT) discharge excited by high current microsecond pulsed hollow cathode lamp (HCMP HCL) has been developed. The operation conditions for Ca atomic and ionic fluorescence spectrometry have been optimized. Compared with atomic fluorescence spectrometry (AFS) in argon microwave induced plasma (MIP) and MPT with the excitation of direct current and conventional pulsed HCL, the system with HCMP HCL excitation can improve AFS and ionic fluorescence spectrometry (IFS) detection limits in MPT atomizer and ionizer. Detection limits (3 sigma) with HCMP HCL-MPT-AFS/IFS are 10.1 ng.mL-1 for Ca I 422.7 nm, 14.6 ng.mL-1 for Ca II 393.4 nm, and 37.4 ng.mL-1 for Ca II 396.8 nm, respectively.

Low-energy electron scattering from atomic hydrogen. II. Elastic and inelastic scattering

DOE Office of Scientific and Technical Information (OSTI.GOV)

James, K.E. Jr.; Childers, J.G.; Khakoo, M.A.

2004-02-01

We present measurements of differential cross sections for elastic electron scattering from atomic hydrogen at 20 eV and 40 eV incident electron energies and ratios of differential cross sections for electron-impact excitation of atomic hydrogen to the n=2, 3, and 4 levels at incident electron energies of 14.6 eV, 15.6 eV, 17.6 eV, 20 eV, 25 eV, and 40 eV with scattering angles ranging from 10 deg. to 130 deg. We compare our results to available experimental measurements and recent convergent close-coupling calculations. Our results resolve significant discrepancies that existed between theory and past experiments.

Proton-proton elastic scattering excitation functions at intermediate energies

NASA Astrophysics Data System (ADS)

Rohdjess, H.

1998-05-01

Polarized and unpolarized proton-proton elastic scattering is investigated with the EDDA-experiment at the Cooler Synchrotron COSY at Jülich to significantly improve the world data base in the beam energy range 500-2500 MeV. Measurements during beam acceleration with thin internal targets and a large acceptance detector provide excitation functions over a broad angular and energy range with unprecedented internal consistency. Data taking with an unpolarized CH2 fiber target and an unpolarized beam have been completed and the derived differential cross sections are presented and compared to a recent phase shift analysis. With a polarized atomic beam target newly installed in COSY and a polarized COSY beam—currently under development—the measurements will be extended to analyzing powers and spin correlation parameters.

Collisional excitation of the highly excited hydrogen atoms in the dipole form of the semiclassical impact parameter and Born approximations

NASA Technical Reports Server (NTRS)

Omidvar, K.

1971-01-01

Expressions for the excitation cross section of the highly excited states of the hydrogenlike atoms by fast charged particles have been derived in the dipole approximation of the semiclassical impact parameter and the Born approximations, making use of a formula for the asymptotic expansion of the oscillator strength of the hydrogenlike atoms given by Menzel. When only the leading term in the asymptotic expansion is retained, the expression for the cross section becomes identical to the expression obtained by the method of the classical collision and correspondence principle given by Percival and Richards. Comparisons are made between the Bethe coefficients obtained here and the Bethe coefficients of the Born approximation for transitions where the Born calculation is available. Satisfactory agreement is obtained only for n yields n + 1 transitions, with n the principal quantum number of the excited state.

{{\\rm{H}}}_{2}\\,X{}^{1}{{\\rm{\\Sigma }}}_{g}^{+}-c{}^{3}{{\\rm{\\Pi }}}_{u} Excitation by Electron Impact: Energies, Spectra, Emission Yields, Cross-sections, and H(1s) Kinetic Energy Distributions

NASA Astrophysics Data System (ADS)

Liu, Xianming; Shemansky, Donald E.; Yoshii, Jean; Liu, Melinda J.; Johnson, Paul V.; Malone, Charles P.; Khakoo, Murtadha A.

2017-10-01

The c{}3{{{\\Pi }}}u state of the hydrogen molecule has the second largest triplet-state excitation cross-section, and plays an important role in the heating of the upper thermospheres of outer planets by electron excitation. Precise energies of the H2, D2, and HD c{}3{{{\\Pi }}}u-(v,N) levels are calculated from highly accurate ab initio potential energy curves that include relativistic, radiative, and empirical non-adiabatic corrections. The emission yields are determined from predissociation rates and refined radiative transition probabilities. The excitation function and excitation cross-section of the c{}3{{{\\Pi }}}u state are extracted from previous theoretical calculations and experimental measurements. The emission cross-section is determined from the calculated emission yield and the extracted excitation cross-section. The kinetic energy (E k ) distributions of H atoms produced via the predissociation of the c{}3{{{\\Pi }}}u state, the c{}3{{{\\Pi }}}u- - b{}3{{{Σ }}}u+ dissociative emission by the magnetic dipole and electric quadrupole, and the c{}3{{{\\Pi }}}u - a{}3{{{Σ }}}g+ - b{}3{{{Σ }}}u+ cascade dissociative emission by the electric dipole are obtained. The predissociation of the c{}3{{{\\Pi }}}u+ and c{}3{{{\\Pi }}}u- states both produce H(1s) atoms with an average E k of ˜4.1 eV/atom, while the c{}3{{{\\Pi }}}u- - b{}3{{{Σ }}}u+ dissociative emissions by the magnetic dipole and electric quadrupole give an average E k of ˜1.0 and ˜0.8 eV/atom, respectively. The c{}3{{{\\Pi }}}u - a{}3{{{Σ }}}g+ - b{}3{{{Σ }}}u+ cascade and dissociative emission gives an average E k of ˜1.3 eV/atom. On average, each H2 excited to the c{}3{{{\\Pi }}}u state in an H2-dominated atmosphere deposits ˜7.1 eV into the atmosphere while each H2 directly excited to the a{}3{{{Σ }}}g+ and d{}3{{{\\Pi }}}u states contribute ˜2.3 and ˜3.3 eV, respectively, to the atmosphere. The spectral distribution of the calculated continuum emission arising from the X{}1{{{�

Laser excited atomic fluorescence spectrometry as a powerful tool for analytical applications and spectroscopic studies

NASA Astrophysics Data System (ADS)

Gornushkin, Igor B.

1997-12-01

Laser-excited atomic fluorescence spectrometry (LEAFS) with a novel diffusive tube electrothermal atomizer (ETA) has been used for the study of atomization and diffusion processes and for the direct trace analysis of complex matrices. A novel ETA was a graphite tube sealed by two graphite electrodes. A sample was introduced into the tube and the furnace assembly was heated. The vaporized sample diffused through the hot graphite and the atomic fraction of the vapor was excited by a tunable dye laser above the tube. Temporal behavior of atomic fluorescence of Cu, Ag, and Ni atoms, diffused through the furnace tube, was studied at different temperatures; the values for activation energies and diffusion coefficients were derived on the basis of the diffusion/vaporization kinetic model. The femtogram/nanogram concentrations of silver were determined in coastal Atlantic water and soil samples. Use of the new ETA resulted in significant reduction of matrix interferences, ultra-low limits of detection, good accuracy and precision. LEAFS coupled with laser ablation (LA) was studied in terms of its analytical and spectroscopic potential. Low concentrations of lead (0.15 ppm-750 ppm) in metallic matrices (copper, brass, steel, and zinc) were measured in a low pressure argon atmosphere. No matrix effect was observed, providing a universal calibration curve for all samples. A limit of detection of 22 ppb (0.5 fg) was achieved. Also, the lifetime of the metastable 6p21D level of lead was measured and found to be in good agreement with the literature data. A simple open-air LA-LEAFS system was used for the determination of cobalt in solid matrices (graphite, soil, and steel). The fluorescence of cobalt was excited from a level which was already populated in the ablation plasma and was monitored at the Stokes-shifted wavelength. Detection limits in the ppb to ppm range and linearity over four orders of magnitude were achieved. The resonance shadowgraph technique has been developed

Excitation energies from range-separated time-dependent density and density matrix functional theory.

PubMed

Pernal, Katarzyna

2012-05-14

Time-dependent density functional theory (TD-DFT) in the adiabatic formulation exhibits known failures when applied to predicting excitation energies. One of them is the lack of the doubly excited configurations. On the other hand, the time-dependent theory based on a one-electron reduced density matrix functional (time-dependent density matrix functional theory, TD-DMFT) has proven accurate in determining single and double excitations of H(2) molecule if the exact functional is employed in the adiabatic approximation. We propose a new approach for computing excited state energies that relies on functionals of electron density and one-electron reduced density matrix, where the latter is applied in the long-range region of electron-electron interactions. A similar approach has been recently successfully employed in predicting ground state potential energy curves of diatomic molecules even in the dissociation limit, where static correlation effects are dominating. In the paper, a time-dependent functional theory based on the range-separation of electronic interaction operator is rigorously formulated. To turn the approach into a practical scheme the adiabatic approximation is proposed for the short- and long-range components of the coupling matrix present in the linear response equations. In the end, the problem of finding excitation energies is turned into an eigenproblem for a symmetric matrix. Assignment of obtained excitations is discussed and it is shown how to identify double excitations from the analysis of approximate transition density matrix elements. The proposed method used with the short-range local density approximation (srLDA) and the long-range Buijse-Baerends density matrix functional (lrBB) is applied to H(2) molecule (at equilibrium geometry and in the dissociation limit) and to Be atom. The method accounts for double excitations in the investigated systems but, unfortunately, the accuracy of some of them is poor. The quality of the other

A long-range-corrected density functional that performs well for both ground-state properties and time-dependent density functional theory excitation energies, including charge-transfer excited states.

PubMed

Rohrdanz, Mary A; Martins, Katie M; Herbert, John M

2009-02-07

We introduce a hybrid density functional that asymptotically incorporates full Hartree-Fock exchange, based on the long-range-corrected exchange-hole model of Henderson et al. [J. Chem. Phys. 128, 194105 (2008)]. The performance of this functional, for ground-state properties and for vertical excitation energies within time-dependent density functional theory, is systematically evaluated, and optimal values are determined for the range-separation parameter, omega, and for the fraction of short-range Hartree-Fock exchange. We denote the new functional as LRC-omegaPBEh, since it reduces to the standard PBEh hybrid functional (also known as PBE0 or PBE1PBE) for a certain choice of its two parameters. Upon optimization of these parameters against a set of ground- and excited-state benchmarks, the LRC-omegaPBEh functional fulfills three important requirements: (i) It outperforms the PBEh hybrid functional for ground-state atomization energies and reaction barrier heights; (ii) it yields statistical errors comparable to PBEh for valence excitation energies in both small and medium-sized molecules; and (iii) its performance for charge-transfer excitations is comparable to its performance for valence excitations. LRC-omegaPBEh, with the parameters determined herein, is the first density functional that satisfies all three criteria. Notably, short-range Hartree-Fock exchange appears to be necessary in order to obtain accurate ground-state properties and vertical excitation energies using the same value of omega.

Tunnel ionization of highly excited atoms in a noncoherent laser radiation field

DOE Office of Scientific and Technical Information (OSTI.GOV)

Krainov, V.P.; Todirashku, S.S.

1982-10-01

A theory is developed of the ionization of highly excited atomic states by a low-frequency field of noncoherent laser radiation with a large number of modes. Analytic formulas are obtained for the probability of the tunnel ionization in such a field. An analysis is made of the case of the hydrogen atom when the parabolic quantum numbers are sufficiently good in the low-frequency limit, as well as of the case of highly excited states of complex atoms when these states are characterized by a definite orbital momentum and parity. It is concluded that the statistical factor representing the ratio ofmore » the probability in a stochastic field to the probability in a monochromatic field decreases, compared with the case of a short-range potential, if the ''Coulomb tail'' is included. It is shown that at a given field intensity the statistical factor decreases on increase in the principal quantum number of the state being ionized.« less

Reduced-cost second-order algebraic-diagrammatic construction method for excitation energies and transition moments

NASA Astrophysics Data System (ADS)

Mester, Dávid; Nagy, Péter R.; Kállay, Mihály

2018-03-01

A reduced-cost implementation of the second-order algebraic-diagrammatic construction [ADC(2)] method is presented. We introduce approximations by restricting virtual natural orbitals and natural auxiliary functions, which results, on average, in more than an order of magnitude speedup compared to conventional, density-fitting ADC(2) algorithms. The present scheme is the successor of our previous approach [D. Mester, P. R. Nagy, and M. Kállay, J. Chem. Phys. 146, 194102 (2017)], which has been successfully applied to obtain singlet excitation energies with the linear-response second-order coupled-cluster singles and doubles model. Here we report further methodological improvements and the extension of the method to compute singlet and triplet ADC(2) excitation energies and transition moments. The various approximations are carefully benchmarked, and conservative truncation thresholds are selected which guarantee errors much smaller than the intrinsic error of the ADC(2) method. Using the canonical values as reference, we find that the mean absolute error for both singlet and triplet ADC(2) excitation energies is 0.02 eV, while that for oscillator strengths is 0.001 a.u. The rigorous cutoff parameters together with the significantly reduced operation count and storage requirements allow us to obtain accurate ADC(2) excitation energies and transition properties using triple-ζ basis sets for systems of up to one hundred atoms.

New energy levels of atomic niobium (Nb I) discovered by laser-spectroscopic investigations

NASA Astrophysics Data System (ADS)

Kröger, S.; Windholz, L.; Başar, Gü.; Başar, Gö.

2018-06-01

We report the discovery of 9 previously unknown energy levels of the atomic niobium, all having even parity. Two levels have energies below 19,500 cm-1 and angular momentum J = 3/2, while the energies of the others are located between 39,700 and 43,420 cm-1. The levels were discovered by laser excitation of several unclassified spectral lines in the wavelength range between 554 nm and 650 nm and detection of laser-induced fluorescence with a monochromator.

Magnetizabilities of relativistic hydrogenlike atoms in some arbitrary discrete energy eigenstates

NASA Astrophysics Data System (ADS)

Stefańska, Patrycja

2016-03-01

We present the results of numerical calculations of magnetizability (χ) of the relativistic one-electron atoms with a pointlike, spinless and motionless nuclei of charge Ze. Exploiting the analytical formula for χ recently derived by us Stefańska (2015), valid for an arbitrary discrete energy eigenstate, we have found the values of the magnetizability for the ground state and for the first and the second set of excited states (i.e.: 2s1/2, 2p1/2, 2p3/2, 3s1/2, 3p1/2, 3p3/2, 3d3/2, and 3d5/2) of the Dirac one-electron atom. The results for ions with the atomic number 1 ⩽ Z ⩽ 137 are given in 14 tables. The comparison of the numerical values of magnetizabilities for the ground state and for each state belonging to the first set of excited states of selected hydrogenlike ions, obtained with the use of two different values of the fine-structure constant, i.e.: α-1 = 137.035 999 139 (CODATA 2014) and α-1 = 137.035 999 074 (CODATA 2010), is also presented.

Low-loss electron energy loss spectroscopy: An atomic-resolution complement to optical spectroscopies and application to graphene

DOE PAGES

Kapetanakis, Myron; Zhou, Wu; Oxley, Mark P.; ...

2015-09-25

Photon-based spectroscopies have played a central role in exploring the electronic properties of crystalline solids and thin films. They are a powerful tool for probing the electronic properties of nanostructures, but they are limited by lack of spatial resolution. On the other hand, electron-based spectroscopies, e.g., electron energy loss spectroscopy (EELS), are now capable of subangstrom spatial resolution. Core-loss EELS, a spatially resolved analog of x-ray absorption, has been used extensively in the study of inhomogeneous complex systems. In this paper, we demonstrate that low-loss EELS in an aberration-corrected scanning transmission electron microscope, which probes low-energy excitations, combined with amore » theoretical framework for simulating and analyzing the spectra, is a powerful tool to probe low-energy electron excitations with atomic-scale resolution. The theoretical component of the method combines density functional theory–based calculations of the excitations with dynamical scattering theory for the electron beam. We apply the method to monolayer graphene in order to demonstrate that atomic-scale contrast is inherent in low-loss EELS even in a perfectly periodic structure. The method is a complement to optical spectroscopy as it probes transitions entailing momentum transfer. The theoretical analysis identifies the spatial and orbital origins of excitations, holding the promise of ultimately becoming a powerful probe of the structure and electronic properties of individual point and extended defects in both crystals and inhomogeneous complex nanostructures. The method can be extended to probe magnetic and vibrational properties with atomic resolution.« less

Steady-state entanglement in levitated optomechanical systems coupled to a higher order excited atomic ensemble

NASA Astrophysics Data System (ADS)

Chen, Aixi; Nie, Wenjie; Li, Ling; Zeng, Wei; Liao, Qinghong; Xiao, Xianbo

2017-11-01

We investigate the steady-state entanglement in an optomechanical system with a levitated dielectric nanosphere and a higher order excited atomic ensemble. The single nanosphere is trapped by an external harmonic dipole trap and coupled to the single-mode cavity field by the effective optomechanical coupling, which depends on the steady-state position of the nanosphere. We show that the steady-state optomechanical entanglement can be generated via the effective optomechanical interaction between the mechanical motion and the cavity mode. Further, these exist an optimal effective cavity detuning that maximizes the optomechanical entanglement. We also analyze in detail the influences of the excitation number of atoms, the radius of the nanosphere and the thermal noise strength on the steady-state optomechanical entanglement. It is found that the steady-state entanglement can be enhanced by increasing the excitation number of atoms and the radius of the nanosphere.

Atom Interferometry on Atom Chips - A Novel Approach Towards Precision Inertial Navigation System - PINS

DTIC Science & Technology

2010-06-01

Demonstration of an area-enclosing guided-atom interferometer for rotation sensing, Phys. Rev. Lett. 99, 173201 (2007). 4. Heralded Single- Magnon Quantum...excitations are quantized spin waves ( magnons ), such that transitions between its energy levels ( magnon number states) correspond to highly directional...polarization storage in the form of a single collective-spin excitation ( magnon ) that is shared between two spatially overlapped atomic ensembles

Resonance interaction energy between two entangled atoms in a photonic bandgap environment.

PubMed

Notararigo, Valentina; Passante, Roberto; Rizzuto, Lucia

2018-03-26

We consider the resonance interaction energy between two identical entangled atoms, where one is in the excited state and the other in the ground state. They interact with the quantum electromagnetic field in the vacuum state and are placed in a photonic-bandgap environment with a dispersion relation quadratic near the gap edge and linear for low frequencies, while the atomic transition frequency is assumed to be inside the photonic gap and near its lower edge. This problem is strictly related to the coherent resonant energy transfer between atoms in external environments. The analysis involves both an isotropic three-dimensional model and the one-dimensional case. The resonance interaction asymptotically decays faster with distance compared to the free-space case, specifically as 1/r 2 compared to the 1/r free-space dependence in the three-dimensional case, and as 1/r compared to the oscillatory dependence in free space for the one-dimensional case. Nonetheless, the interaction energy remains significant and much stronger than dispersion interactions between atoms. On the other hand, spontaneous emission is strongly suppressed by the environment and the correlated state is thus preserved by the spontaneous-decay decoherence effects. We conclude that our configuration is suitable for observing the elusive quantum resonance interaction between entangled atoms.

Charge transfer in low-energy collisions of H with He+ and H+ with He in excited states

NASA Astrophysics Data System (ADS)

Loreau, J.; Ryabchenko, S.; Muñoz Burgos, J. M.; Vaeck, N.

2018-04-01

The charge transfer process in collisions of excited (n = 2, 3) hydrogen atoms with He+ and in collisions of excited helium atoms with H+ is studied theoretically. A combination of a fully quantum-mechanical method and a semi-classical approach is employed to calculate the charge-exchange cross sections at collision energies from 0.1 eV u‑1 up to 1 keV u‑1. These methods are based on accurate ab initio potential energy curves and non-adiabatic couplings for the molecular ion HeH+. Charge transfer can occur either in singlet or in triplet states, and the differences between the singlet and triplet spin manifolds are discussed. The dependence of the cross section on the quantum numbers n and l of the initial state is demonstrated. The isotope effect on the charge transfer cross sections, arising at low collision energy when H is substituted by D or T, is investigated. Rate coefficients are calculated for all isotopes up to 106 K. Finally, the impact of the present calculations on models of laboratory plasmas is discussed.

Energy shift and Casimir-Polder force for an atom out of thermal equilibrium near a dielectric substrate

NASA Astrophysics Data System (ADS)

Zhou, Wenting; Yu, Hongwei

2014-09-01

We study the energy shift and the Casimir-Polder force of an atom out of thermal equilibrium near the surface of a dielectric substrate. We first generalize, adopting the local source hypothesis, the formalism proposed by Dalibard, Dupont-Roc, and Cohen-Tannoudji [J. Phys. (Paris) 43, 1617 (1982), 10.1051/jphys:0198200430110161700; J. Phys. (Paris) 45, 637 (1984), 10.1051/jphys:01984004504063700], which separates the contributions of thermal fluctuations and radiation reaction to the energy shift and allows a distinct treatment of atoms in the ground and excited states, to the case out of thermal equilibrium, and then we use the generalized formalism to calculate the energy shift and the Casimir-Polder force of an isotropically polarizable neutral atom. We identify the effects of the thermal fluctuations that originate from the substrate and the environment and discuss in detail how the Casimir-Polder force out of thermal equilibrium behaves in three different distance regions in both the low-temperature limit and the high-temperature limit for both the ground-state and excited-state atoms, with special attention devoted to the distinctive features as opposed to thermal equilibrium. In particular, we recover the distinctive behavior of the atom-wall force out of thermal equilibrium at large distances in the low-temperature limit recently found in a different theoretical framework, and furthermore we give a concrete region where this behavior holds.

Low energy collisions of spin-polarized metastable argon atoms with ground state argon atoms

NASA Astrophysics Data System (ADS)

Taillandier-Loize, T.; Perales, F.; Baudon, J.; Hamamda, M.; Bocvarski, V.; Ducloy, M.; Correia, F.; Fabre, N.; Dutier, G.

2018-04-01

The collision between a spin-polarized metastable argon atom in Ar* (3p54s, 3P2, M = +2) state slightly decelerated by the Zeeman slower-laser technique and a co-propagating thermal ground state argon atom Ar (3p6, 1S0), both merged from the same supersonic beam, but coming through adjacent slots of a rotating disk, is investigated at the center of mass energies ranging from 1 to 10 meV. The duration of the laser pulse synchronised with the disk allows the tuning of the relative velocity and thus the collision energy. At these sub-thermal energies, the ‘resonant metastability transfer’ signal is too small to be evidenced. The explored energy range requires using indiscernibility amplitudes for identical isotopes to have a correct interpretation of the experimental results. Nevertheless, excitation transfers are expected to increase significantly at much lower energies as suggested by previous theoretical predictions of potentials 2g(3P2) and 2u(3P2). Limits at ultra-low collisional energies of the order of 1 mK (0.086 μeV) or less, where gigantic elastic cross sections are expected, will also be discussed. The experimental method is versatile and could be applied using different isotopes of Argon like 36Ar combined with 40Ar, as well as other rare gases among which Krypton should be of great interest thanks to the available numerous isotopes present in a natural gas mixture.

[Microsecond Pulsed Hollow Cathode Lamp as Enhanced Excitation Source of Hydride Generation Atomic Fluorescence Spectrometry].

PubMed

Zhang, Shuo

2015-09-01

The spectral, electrical and atomic fluorescence characteristics of As, Se, Sb and Pb hollow cathode lamps (HCLs) powered by a laboratory-built high current microsecond pulse (HCMP) power supply were studied, and the feasibility of using HCMP-HCLs as the excitation source of hydride generation atomic fluorescence spectrometry (HG-AFS) was evaluated. Under the HCMP power supply mode, the As, Se, Sb, Pb HCLs can maintain stable glow discharge at frequency of 100~1000 Hz, pulse width of 4.0~20 μs and pulse current up to 4.0 A. Relationship between the intensity of characteristic emission lines and HCMP power supply parameters, such as pulse current, power supply voltage, pulse width and frequency, was studied in detail. Compared with the conventional pulsed (CP) HCLs used in commercial AFS instruments, HCMP-HCLs have a narrower pulse width and much stronger pulse current. Under the optimized HCMP power supply parameters, the intensity of atomic emission lines of As, Se, Sb HCLs had sharp enhancement and that indicated their capacity of being a novel HG-AFS excitation source. However, the attenuation of atomic lines and enhancement of ionic lines negated such feasibility of HCMP-Pb HCL. Then the HG-AFS analytical capability of using the HCMP-As/Se/Sb HCLs excitation source was established and results showed that the HCMP-HCL is a promising excitation source for HG-AFS.

Calculating constants of the rates of the reactions of excitation, ionization, and atomic exchange: A model of a shock oscillator with a change of the Hamiltonian of the system

NASA Astrophysics Data System (ADS)

Tsyganov, D. L.

2017-11-01

A new model for calculating the rates of reactions of excitation, ionization, and atomic exchange is proposed. Diatomic molecule AB is an unstructured particle M upon the exchange of elastic-vibrational (VT) energy, i.e., a model of a shock forceful oscillator with a change in Hamiltonian (SFOH). The SFOH model is based on the quantum theory of strong perturbations. The SFOH model allows generalization in simulating the rates of the reactions of excitation, ionization, and atomic exchange in the vibrational-vibrational (VV) energy exchange of diatomic molecules, and the exchange of VV- and VT-energy of polyatomic molecules. The rate constants of the excitation of metastables A 3Σ u +, B 3Π g , W 3Δ u , B'3Σ u -, a'3Σ u -, and the ionization of a nitrogen molecules from ground state X2Σ g + upon a collision with a heavy structureless particle (a nitrogen molecule), are found as examples.

Excitation of trapped modes from a metasurface composed of only Z-shaped meta-atoms

NASA Astrophysics Data System (ADS)

Dhouibi, Abdallah; Nawaz Burokur, Shah; Lupu, Anatole; de Lustrac, André; Priou, Alain

2013-10-01

A printed planar Z-shaped meta-atom has recently been proposed as an alternative design to the conventional electric-LC resonator for achieving negative permittivity. Transforming the LC topology of the resonator helps to facilitate transposition of geometrical parameters for the optical regime and also to improve the metamaterial homogeneity. In this work, we discuss about the excitation of a dark or trapped mode in such Z-shaped meta-atom. The electromagnetic behavior of the meta-atom has been investigated through both simulations and experiments in the microwave regime. Our results show that the Z meta-atom exhibits a trapped mode resonance. Depending on the orientation of the polarized electromagnetic field with respect to the Z atom topology and the incident plane, the excitation of the dark mode can lead either to a narrowband resonance in reflection or to a very asymmetric Fano-like resonance in transmission, analog of electromagnetically induced transparency. Compared to other structures, the Z meta-atom presents the advantage of having the dark mode resonance spectrally spaced with respect to the bright mode resonances, which could simplify the observation of the dark mode at much shorter wavelengths.

Low cost estimation of the contribution of post-CCSD excitations to the total atomization energy using density functional theory calculations

NASA Astrophysics Data System (ADS)

Sánchez, H. R.; Pis Diez, R.

2016-04-01

Based on the Aλ diagnostic for multireference effects recently proposed [U.R. Fogueri, S. Kozuch, A. Karton, J.M. Martin, Theor. Chem. Acc. 132 (2013) 1], a simple method for improving total atomization energies and reaction energies calculated at the CCSD level of theory is proposed. The method requires a CCSD calculation and two additional density functional theory calculations for the molecule. Two sets containing 139 and 51 molecules are used as training and validation sets, respectively, for total atomization energies. An appreciable decrease in the mean absolute error from 7-10 kcal mol-1 for CCSD to about 2 kcal mol-1 for the present method is observed. The present method provides atomization energies and reaction energies that compare favorably with relatively recent scaled CCSD methods.

Collisional excitation of NH3 by atomic and molecular hydrogen

NASA Astrophysics Data System (ADS)

Bouhafs, N.; Rist, C.; Daniel, F.; Dumouchel, F.; Lique, F.; Wiesenfeld, L.; Faure, A.

2017-09-01

We report extensive theoretical calculations on the rotation-inversion excitation of interstellar ammonia (NH3) due to collisions with atomic and molecular hydrogen (both para- and ortho-H2). Close-coupling calculations are performed for total energies in the range 1-2000 cm-1 and rotational cross-sections are obtained for all transitions amongst the lowest 17 and 34 rotation-inversion levels of ortho- and para-NH3, respectively. Rate coefficients are deduced for kinetic temperatures up to 200 K. Propensity rules for the three colliding partners are discussed and we also compare the new results to previous calculations for the spherically symmetrical He and para-H2 projectiles. Significant differences are found between the different sets of calculations. Finally, we test the impact of the new rate coefficients on the calibration of the ammonia thermometer. We find that the calibration curve is only weakly sensitive to the colliding partner and we confirm that the ammonia thermometer is robust.

Analysis of Data on the Cross Sections for Electron-Impact Ionization and Excitation of Electronic States of Atomic Hydrogen (Review)

NASA Astrophysics Data System (ADS)

Shakhatov, V. A.; Lebedev, Yu. A.

2018-01-01

A review is given of experimental and theoretical data on the cross sections for ionization, excitation, and deexcitation of atomic hydrogen. The set of the cross sections required to calculate the electron energy distribution function and find the level-to-level rate coefficients needed to solve balance equations for the densities of neutral and charged particles in hydrogen plasma is determined.

Energy-optimal electrical excitation of nerve fibers.

PubMed

Jezernik, Saso; Morari, Manfred

2005-04-01

We derive, based on an analytical nerve membrane model and optimal control theory of dynamical systems, an energy-optimal stimulation current waveform for electrical excitation of nerve fibers. Optimal stimulation waveforms for nonleaky and leaky membranes are calculated. The case with a leaky membrane is a realistic case. Finally, we compare the waveforms and energies necessary for excitation of a leaky membrane in the case where the stimulation waveform is a square-wave current pulse, and in the case of energy-optimal stimulation. The optimal stimulation waveform is an exponentially rising waveform and necessitates considerably less energy to excite the nerve than a square-wave pulse (especially true for larger pulse durations). The described theoretical results can lead to drastically increased battery lifetime and/or decreased energy transmission requirements for implanted biomedical systems.

Roles of the Excitation in Harvesting Energy from Vibrations

PubMed Central

Zhang, Hui; Ma, Tianwei

2015-01-01

The study investigated the role of excitation in energy harvesting applications. While the energy ultimately comes from the excitation, it was shown that the excitation may not always behave as a source. When the device characteristics do not perfectly match the excitation, the excitation alternately behaves as a source and a sink. The extent to which the excitation behaves as a sink determines the energy harvesting efficiency. Such contradictory roles were shown to be dictated by a generalized phase defined as the instantaneous phase angle between the velocity of the device and the excitation. An inductive prototype device with a diamagnetically levitated seismic mass was proposed to take advantage of the well established phase changing mechanism of vibro-impact to achieve a broader device bandwidth. Results suggest that the vibro-impact can generate an instantaneous, significant phase shift in response velocity that switches the role of the excitation. If introduced properly outside the resonance zone it could dramatically increase the energy harvesting efficiency. PMID:26496183

Ultrafast atomic-scale visualization of acoustic phonons generated by optically excited quantum dots

PubMed Central

Vanacore, Giovanni M.; Hu, Jianbo; Liang, Wenxi; Bietti, Sergio; Sanguinetti, Stefano; Carbone, Fabrizio; Zewail, Ahmed H.

2017-01-01

Understanding the dynamics of atomic vibrations confined in quasi-zero dimensional systems is crucial from both a fundamental point-of-view and a technological perspective. Using ultrafast electron diffraction, we monitored the lattice dynamics of GaAs quantum dots—grown by Droplet Epitaxy on AlGaAs—with sub-picosecond and sub-picometer resolutions. An ultrafast laser pulse nearly resonantly excites a confined exciton, which efficiently couples to high-energy acoustic phonons through the deformation potential mechanism. The transient behavior of the measured diffraction pattern reveals the nonequilibrium phonon dynamics both within the dots and in the region surrounding them. The experimental results are interpreted within the theoretical framework of a non-Markovian decoherence, according to which the optical excitation creates a localized polaron within the dot and a travelling phonon wavepacket that leaves the dot at the speed of sound. These findings indicate that integration of a phononic emitter in opto-electronic devices based on quantum dots for controlled communication processes can be fundamentally feasible. PMID:28852685

Dissociative Excitation of Thymine by Electron Impact

NASA Astrophysics Data System (ADS)

McConkey, William; Tiessen, Collin; Hein, Jeffrey; Trocchi, Joshuah; Kedzierski, Wladek

2014-05-01

A crossed electron-gas beam system coupled to a VUV spectrometer has been used to investigate the dissociation of thymine (C5H6N2O2) into excited atomic fragments in the electron-impact energy range from threshold to 375 eV. A special stainless steel oven is used to vaporize the thymine and form it into a beam where it is intersected by a magnetically collimated electron beam, typical current 50 μA. The main features in the spectrum are the H Lyman series lines. The probability of extracting excited C or N atoms from the ring is shown to be very small. In addition to spectral data, excitation probability curves as a function of electron energy will be presented for the main emission features. Possible dissociation channels and excitation mechanisms in the parent molecule will be discussed. The authors thank NSERC (Canada) for financial support.

Atomic Energy Basics, Understanding the Atom Series.

ERIC Educational Resources Information Center

Atomic Energy Commission, Oak Ridge, TN. Div. of Technical Information.

This booklet is part of the "Understanding the Atom Series," though it is a later edition and not included in the original set of 51 booklets. A basic survey of the principles of nuclear energy and most important applications are provided. These major topics are examined: matter has molecules and atoms, the atom has electrons, the nucleus,…

Sum rules and the role of pressure on the excitation spectrum of a confined hydrogen atom by a spherical cavity

NASA Astrophysics Data System (ADS)

Cabrera-Trujillo, R.

2017-08-01

Sum rule relations over the excitation spectrum of a quantum system contain information about both the energy spectrum and eigenfunctions of the system in a compact form, particularly regarding closure relations. In this work, the effects of pressure induced by a spherical cavity on an atomic hydrogen impurity on the dipole oscillator strength (DOS) sum rule, S k , and its logarithmic version, L k , are studied by means of a numerical approach based on a finite-difference solution to the Schrödinger equation. Pressure effects are accounted for by means of a spherical cavity of radius R 0 immersed in a medium characterized by a penetrable potential height V 0. The DOS sum rules S k and L k are investigated as a function of these cavity parameters and thus directly related to the impurity static pressure and surrounding material. One finds that the sum rules are fulfilled within the numerical precision for low pressure conditions. However, when the barrier height is large or infinite (a non-penetrable cavity), the sum rule, for positive k, differs from its closure relation. One finds that this occurs for a cavity radius {R}0< 6 au, corresponding to a pressure such that the first p-state that contributes to the sum rule has positive energy and it is due to the fact that the spherical confinement cavity potential dominates over the Coulombic interaction for the hydrogenic impurity. Thus, as pressure increases, the excitation spectrum approaches that of a particle confined by a spherical cavity while the ground state is slightly affected by the cavity and more closely resembles a hydrogenic atom. Therefore, the sum rule over the excitation spectrum tends to a particle confined by a spherical cavity, while the closure relation gives that of a confined hydrogen atom in the ground state. For negative k, low excitations are the most important and this behavior is not presented. As the {S}-2 sum rule is the static dipole polarizability, the results are compared to available

Reduction of the virtual space for coupled-cluster excitation energies of large molecules and embedded systems

PubMed Central

Send, Robert; Kaila, Ville R. I.; Sundholm, Dage

2011-01-01

We investigate how the reduction of the virtual space affects coupled-cluster excitation energies at the approximate singles and doubles coupled-cluster level (CC2). In this reduced-virtual-space (RVS) approach, all virtual orbitals above a certain energy threshold are omitted in the correlation calculation. The effects of the RVS approach are assessed by calculations on the two lowest excitation energies of 11 biochromophores using different sizes of the virtual space. Our set of biochromophores consists of common model systems for the chromophores of the photoactive yellow protein, the green fluorescent protein, and rhodopsin. The RVS calculations show that most of the high-lying virtual orbitals can be neglected without significantly affecting the accuracy of the obtained excitation energies. Omitting all virtual orbitals above 50 eV in the correlation calculation introduces errors in the excitation energies that are smaller than 0.1 eV . By using a RVS energy threshold of 50 eV , the CC2 calculations using triple-ζ basis sets (TZVP) on protonated Schiff base retinal are accelerated by a factor of 6. We demonstrate the applicability of the RVS approach by performing CC2∕TZVP calculations on the lowest singlet excitation energy of a rhodopsin model consisting of 165 atoms using RVS thresholds between 20 eV and 120 eV. The calculations on the rhodopsin model show that the RVS errors determined in the gas-phase are a very good approximation to the RVS errors in the protein environment. The RVS approach thus renders purely quantum mechanical treatments of chromophores in protein environments feasible and offers an ab initio alternative to quantum mechanics∕molecular mechanics separation schemes. PMID:21663351

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.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Egidi, Franco, E-mail: franco.egidi@sns.it; Segado, Mireia; Barone, Vincenzo, E-mail: vincenzo.barone@sns.it

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.

Dipole polarizability, sum rules, mean excitation energies, and long-range dispersion coefficients for buckminsterfullerene C 60

NASA Astrophysics Data System (ADS)

Kumar, Ashok; Thakkar, Ajit J.

2011-11-01

Experimental photoabsorption cross-sections combined with constraints provided by the Kuhn-Reiche-Thomas sum rule and the high-energy behavior of the dipole-oscillator-strength density are used to construct dipole oscillator strength distributions for buckminsterfullerene (C60). The distributions are used to predict dipole sum rules Sk, mean excitation energies Ik, the frequency dependent polarizability, and C6 coefficients for the long-range dipole-dipole interactions of C60 with a variety of atoms and molecules.

Low-energy electron scattering from atomic hydrogen. I. Ionization

DOE Office of Scientific and Technical Information (OSTI.GOV)

Childers, J.G.; James, K.E. Jr.; Bray, Igor

2004-02-01

Absolute doubly differential cross sections for the ionization of atomic hydrogen by electron impact have been measured at energies ranging from near threshold to intermediate values. The measurements are normalized to the accurate differential cross section for the electron-impact excitation of the H 1 {sup 2}S{yields}2 {sup 2}S+2 {sup 2}P transition. These measurements were made possible through the use of a moveable target source which enables the collection of hydrogen energy loss spectra free of all backgrounds. The measurements cover the incident electron energy range of 14.6-40 eV and scattering angles from 12 deg. to 127 deg., and are inmore » very good agreement with the results of the latest theoretical models--the convergent close-coupling model and the exterior complex scaling model.« less

Atomic, Molecular, and Optical Physics: Optical Excitation Function of H(1s-2p) Produced by electron Impact from Threshold to 1.8 keV

NASA Technical Reports Server (NTRS)

James, G. K.; Slevin, J. A.; Shemansky, D. E.; McConkey, J. W.; Bray, I.; Dziczek, D.; Kanik, I.; Ajello, J. M.

1997-01-01

The optical excitation function of prompt Lyman-Alpha radiation, produced by electron impact on atomic hydrogen, has been measured over the extended energy range from threshold to 1.8 keV. Measurements were obtained in a crossed-beams experiment using both magnetically confined and electrostatically focused electrons in collision with atomic hydrogen produced by an intense discharge source. A vacuum-ultraviolet mono- chromator system was used to measure the emitted Lyman-Alpha radiation. The absolute H(1s-2p) electron impact excitation cross section was obtained from the experimental optical excitation function by normalizing to the accepted optical oscillator strength, with corrections for polarization and cascade. Statistical and known systematic uncertainties in our data range from +/- 4% near threshold to +/- 2% at 1.8 keV. Multistate coupling affecting the shape of the excitation function up to 1 keV impact energy is apparent in both the present experimental data and present theoretical results obtained with convergent close- coupling (CCC) theory. This shape function effect leads to an uncertainty in absolute cross sections at the 10% level in the analysis of the experimental data. The derived optimized absolute cross sections are within 7% of the CCC calculations over the 14 eV-1.8 keV range. The present CCC calculations converge on the Bethe- Fano profile for H(1s-2p) excitation at high energy. For this reason agreement with the CCC values to within 3% is achieved in a nonoptimal normalization of the experimental data to the Bethe-Fano profile. The fundamental H(1s-2p) electron impact cross section is thereby determined to an unprecedented accuracy over the 14 eV - 1.8 keV energy range.

Shell- and subshell-resolved projectile excitation of hydrogenlike Au{sup 78+} ions in relativistic ion-atom collisions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gumberidze, A.; Frankfurt Institute for Advanced Studies FIAS, D-60438 Frankfurt am Main; Fritzsche, S.

2010-11-15

The projectile excitation of high-Z ions has been investigated in relativistic ion-atoms collisions by observing the subsequent x-ray emission. The x-ray spectra from the projectile excitation have been separated from the x-ray emission following electron capture into the excited states using a novel anticoincidence technique. For the particular case of hydrogenlike Au{sup 78+} ions colliding with Ar atoms, Coulomb excitation from the ground state into the fine-structure-resolved n=2 levels as well as into levels with principal quantum number n{>=}3 has been measured with excellent statistics. The observed spectra agree well with simulated spectra that are based on Dirac's relativistic equationmore » and the proper inclusion of the magnetic interaction into the amplitudes for projectile excitation. It is shown that a coherent inclusion of the magnetic part of the Lienard-Wiechert potential leads to the lowering of the excitation cross section by up to 35%. This effect is more pronounced for excitation into states with high angular momentum and is confirmed by our experimental data.« less

The stark effect on the spectrum energy of tritium in first excited state with relativistic condition

NASA Astrophysics Data System (ADS)

Prastowo, S. H. B.; Supriadi, B.; Bahri, S.; Ridlo, Z. R.

2018-04-01

This research discussed about the correction of Stark Effect on Tritium atoms in the first excited state with relativistic conditions. The approach used to solve this Stark Effect correction was the perturbation theory which was from time independent degenerate perturbation theory to second-order correction. The Stark Effect on the excited state made the spectrum energy polarization of Tritium which was included in the isotope of hydrogen with an electron moving around the nucleus with high velocity. Hence, the relativistic correction affected the spectrum energy shift. Tritium was a radioactive material having half-time 12,3 years and relatively safe. The Tritium application was a material for the manufacture of nuclear battery. The most effective external electric field that should give to Tritium was 108 V/mith the total correction energy that was 0,97398557 × 10-21 Joule. Therefore, its effect reduced the binding energy between electron and nucleus, and increased the power of Tritium Betavoltaics Battery.

Excitation-energy influence at the scission configuration

NASA Astrophysics Data System (ADS)

Ramos, D.; Rodríguez-Tajes, C.; Caamaño, M.; Farget, F.; Audouin, L.; Benlliure, J.; Casarejos, E.; Clement, E.; Cortina, D.; Delaune, O.; Derkx, X.; Dijon, A.; Doré, D.; Fernández-Domínguez, B.; de France, G.; Heinz, A.; Jacquot, B.; Navin, A.; Paradela, C.; Rejmund, M.; Roger, T.; Salsac, M.-D.; Schmitt, C.

2017-09-01

Transfer- and fusion-induced fission in inverse kinematics was proven to be a powerful tool to investigate nuclear fission, widening the information of the fission fragments and the access to unstable fissioning systems with respect to other experimental approaches. An experimental campaign for fission investigation has being carried out at GANIL with this technique since 2008. In these experiments, a beam of 238U, accelerated to 6.1 MeV/u, impinges on a 12C target. Fissioning systems from U to Cf are populated through transfer and fusion reactions, with excitation energies that range from few MeV up to 46 MeV. The use of inverse kinematics, the SPIDER telescope, and the VAMOS spectrometer permitted the characterization of the fissioning system in terms of mass, nuclear charge, and excitation energy, and the isotopic identification of the full fragment distribution. The neutron excess, the total neutron multiplicity, and the even-odd staggering in the nuclear charge of fission fragments are presented as a function of the excitation energy of the fissioning system. Structure effects are observed at Z˜50 and Z˜55, where their impact evolves with the excitation energy.

Reduction of the virtual space for coupled-cluster excitation energies of large molecules and embedded systems.

PubMed

Send, Robert; Kaila, Ville R I; Sundholm, Dage

2011-06-07

We investigate how the reduction of the virtual space affects coupled-cluster excitation energies at the approximate singles and doubles coupled-cluster level (CC2). In this reduced-virtual-space (RVS) approach, all virtual orbitals above a certain energy threshold are omitted in the correlation calculation. The effects of the RVS approach are assessed by calculations on the two lowest excitation energies of 11 biochromophores using different sizes of the virtual space. Our set of biochromophores consists of common model systems for the chromophores of the photoactive yellow protein, the green fluorescent protein, and rhodopsin. The RVS calculations show that most of the high-lying virtual orbitals can be neglected without significantly affecting the accuracy of the obtained excitation energies. Omitting all virtual orbitals above 50 eV in the correlation calculation introduces errors in the excitation energies that are smaller than 0.1 eV. By using a RVS energy threshold of 50 eV, the CC2 calculations using triple-ζ basis sets (TZVP) on protonated Schiff base retinal are accelerated by a factor of 6. We demonstrate the applicability of the RVS approach by performing CC2/TZVP calculations on the lowest singlet excitation energy of a rhodopsin model consisting of 165 atoms using RVS thresholds between 20 eV and 120 eV. The calculations on the rhodopsin model show that the RVS errors determined in the gas-phase are a very good approximation to the RVS errors in the protein environment. The RVS approach thus renders purely quantum mechanical treatments of chromophores in protein environments feasible and offers an ab initio alternative to quantum mechanics/molecular mechanics separation schemes. © 2011 American Institute of Physics

Coulomb displacement energies of excited states

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sherr, R.; Bertsch, G.

The Bansal--French--Zamick model is quite successful in accounting for the Coulomb displacement energies of excited particle--hole states in a variety of light nuclei. Level shifts are typically reproduced to within 50 keV. However, the model fails for certain excited 0$sup +$ states, and this remains a puzzle. (AIP)

Evaluating excited state atomic polarizabilities of chromophores† †Electronic supplementary information (ESI) available: Basis set dependence, definition of bond charges, Romberg differentiation, python script to calculate atomic polarizabilities, influence of the cavity radius, atomic polarizabilities of coumarin 153, all tables in atomic units. See DOI: 10.1039/c7cp08549d

PubMed Central

Heid, Esther

2018-01-01

Ground and excited state dipoles and polarizabilities of the chromophores N-methyl-6-oxyquinolinium betaine (MQ) and coumarin 153 (C153) in solution have been evaluated using time-dependent density functional theory (TD-DFT). A method for determining the atomic polarizabilities has been developed; the molecular dipole has been decomposed into atomic charge transfer and polarizability terms, and variation in the presence of an electric field has been used to evaluate atomic polarizabilities. On excitation, MQ undergoes very site-specific changes in polarizability while C153 shows significantly less variation. We also conclude that MQ cannot be adequately described by standard atomic polarizabilities based on atomic number and hybridization state. Changes in the molecular polarizability of MQ (on excitation) are not representative of the local site-specific changes in atomic polarizability, thus the overall molecular polarizability ratio does not provide a good approximation for local atom-specific polarizability changes on excitation. Accurate excited state force fields are needed for computer simulation of solvation dynamics. The chromophores considered in this study are often used as molecular probes. The methods and data reported here can be used for the construction of polarizable ground and excited state force fields. Atomic and molecular polarizabilities (ground and excited states) have been evaluated over a range of functionals and basis sets. Different mechanisms for including solvation effects have been examined; using a polarizable continuum model, explicit solvation and via sampling of clusters extracted from a MD simulation. A range of different solvents have also been considered. PMID:29542743

Multiconfiguration pair-density functional theory for doublet excitation energies and excited state geometries: the excited states of CN.

PubMed

Bao, Jie J; Gagliardi, Laura; Truhlar, Donald G

2017-11-15

Multiconfiguration pair-density functional theory (MC-PDFT) is a post multiconfiguration self-consistent field (MCSCF) method with similar performance to complete active space second-order perturbation theory (CASPT2) but with greater computational efficiency. Cyano radical (CN) is a molecule whose spectrum is well established from experiments and whose excitation energies have been used as a testing ground for theoretical methods to treat excited states of open-shell systems, which are harder and much less studied than excitation energies of closed-shell singlets. In the present work, we studied the adiabatic excitation energies of CN with MC-PDFT. Then we compared this multireference (MR) method to some single-reference (SR) methods, including time-dependent density functional theory (TDDFT) and completely renormalized equation-of-motion coupled-cluster theory with singles, doubles and noniterative triples [CR-EOM-CCSD(T)]; we also compared to some other MR methods, including configuration interaction singles and doubles (MR-CISD) and multistate CASPT2 (MS-CASPT2). Through a comparison between SR and MR methods, we achieved a better appreciation of the need to use MR methods to accurately describe higher excited states, and we found that among the MR methods, MC-PDFT stands out for its accuracy for the first four states out of the five doublet states studied this paper; this shows its efficiency for calculating doublet excited states.

Sub-kilohertz excitation lasers for quantum information processing with Rydberg atoms

NASA Astrophysics Data System (ADS)

Legaie, Remy; Picken, Craig J.; Pritchard, Jonathan D.

2018-04-01

Quantum information processing using atomic qubits requires narrow linewidth lasers with long-term stability for high fidelity coherent manipulation of Rydberg states. In this paper, we report on the construction and characterization of three continuous-wave (CW) narrow linewidth lasers stabilized simultaneously to an ultra-high finesse Fabry-Perot cavity made of ultra-low expansion (ULE) glass, with a tunable offset-lock frequency. One laser operates at 852~nm while the two locked lasers at 1018~nm are frequency doubled to 509~nm for excitation of $^{133}$Cs atoms to Rydberg states. The optical beatnote at 509~nm is measured to be 260(5)~Hz. We present measurements of the offset between the atomic and cavity resonant frequencies using electromagnetically induced transparency (EIT) for high-resolution spectroscopy on a cold atom cloud. The long-term stability is determined from repeated spectra over a period of 20 days yielding a linear frequency drift of $\\sim1$~Hz/s.

Cooling by spontaneous decay of highly excited antihydrogen atoms in magnetic traps.

PubMed

Pohl, T; Sadeghpour, H R; Nagata, Y; Yamazaki, Y

2006-11-24

An efficient cooling mechanism of magnetically trapped, highly excited antihydrogen (H) atoms is presented. This cooling, in addition to the expected evaporative cooling, results in trapping of a large number of H atoms in the ground state. It is found that the final fraction of trapped atoms is insensitive to the initial distribution of H magnetic quantum numbers. Expressions are derived for the cooling efficiency, demonstrating that magnetic quadrupole (cusp) traps provide stronger cooling than higher order magnetic multipoles. The final temperature of H confined in a cusp trap is shown to depend as approximately 2.2T(n0)n(0)(-2/3) on the initial Rydberg level n0 and temperature T(n0).

Carrier-Envelope Phase Effect on Atomic Excitation by Few-Cycle rf Pulses

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li Hebin; Welch, George R.; Sautenkov, Vladimir A.

2010-03-12

We present an experimental and theoretical study of the carrier-envelope phase effects on population transfer between two bound atomic states interacting with intense ultrashort pulses. Radio frequency pulses are used to transfer population among the ground state hyperfine levels in rubidium atoms. These pulses are only a few cycles in duration and have Rabi frequencies of the order of the carrier frequency. The phase difference between the carrier and the envelope of the pulses has a significant effect on the excitation of atomic coherence and population transfer. We provide a theoretical description of this phenomenon using density matrix equations. Wemore » discuss the implications and possible applications of our results.« less

Measurement-induced entanglement for excitation stored in remote atomic ensembles.

PubMed

Chou, C W; de Riedmatten, H; Felinto, D; Polyakov, S V; van Enk, S J; Kimble, H J

2005-12-08

A critical requirement for diverse applications in quantum information science is the capability to disseminate quantum resources over complex quantum networks. For example, the coherent distribution of entangled quantum states together with quantum memory (for storing the states) can enable scalable architectures for quantum computation, communication and metrology. Here we report observations of entanglement between two atomic ensembles located in distinct, spatially separated set-ups. Quantum interference in the detection of a photon emitted by one of the samples projects the otherwise independent ensembles into an entangled state with one joint excitation stored remotely in 10(5) atoms at each site. After a programmable delay, we confirm entanglement by mapping the state of the atoms to optical fields and measuring mutual coherences and photon statistics for these fields. We thereby determine a quantitative lower bound for the entanglement of the joint state of the ensembles. Our observations represent significant progress in the ability to distribute and store entangled quantum states.

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

Interatomic Coulombic decay cascades in multiply excited neon clusters

PubMed Central

Nagaya, K.; Iablonskyi, D.; Golubev, N. V.; Matsunami, K.; Fukuzawa, H.; Motomura, K.; Nishiyama, T.; Sakai, T.; Tachibana, T.; Mondal, S.; Wada, S.; Prince, K. C.; Callegari, C.; Miron, C.; Saito, N.; Yabashi, M.; Demekhin, Ph. V.; Cederbaum, L. S.; Kuleff, A. I.; Yao, M.; Ueda, K.

2016-01-01

In high-intensity laser light, matter can be ionized by direct multiphoton absorption even at photon energies below the ionization threshold. However on tuning the laser to the lowest resonant transition, the system becomes multiply excited, and more efficient, indirect ionization pathways become operative. These mechanisms are known as interatomic Coulombic decay (ICD), where one of the species de-excites to its ground state, transferring its energy to ionize another excited species. Here we show that on tuning to a higher resonant transition, a previously unknown type of interatomic Coulombic decay, intra-Rydberg ICD occurs. In it, de-excitation of an atom to a close-lying Rydberg state leads to electron emission from another neighbouring Rydberg atom. Moreover, systems multiply excited to higher Rydberg states will decay by a cascade of such processes, producing even more ions. The intra-Rydberg ICD and cascades are expected to be ubiquitous in weakly-bound systems exposed to high-intensity resonant radiation. PMID:27917867

A quasi-classical study of energy transfer in collisions of hyperthermal H atoms with SO2 molecules.

PubMed

da Silva, Ramon S; Garrido, Juan D; Ballester, Maikel Y

2017-08-28

A deep understanding of energy transfer processes in molecular collisions is at central attention in physical chemistry. Particularly vibrational excitation of small molecules colliding with hot light atoms, via a metastable complex formation, has shown to be an efficient manner of enhancing reactivity. A quasi-classical trajectory study of translation-to-vibration energy transfer (T-V ET) in collisions of hyperthermal H( 2 S) atoms with SO 2 (X̃ 1 A ' ) molecules is presented here. For such a study, a double many-body expansion potential energy surface previously reported for HSO 2 ( 2 A) is used. This work was motivated by recent experiments by Ma et al. studying collisions of H + SO 2 at the translational energy of 59 kcal/mol [J. Ma et al., Phys. Rev. A 93, 040702 (2016)]. Calculations reproduce the experimental evidence that during majority of inelastic non-reactive collision processes, there is a metastable intermediate formation (HOSO or HSO 2 ). Nevertheless, the analysis of the trajectories shows that there are two distinct mechanisms in the T-V ET process: direct and indirect. Direct T-V processes are responsible for the high population of SO 2 with relatively low vibrational excitation energy, while indirect ones dominate the conversion from translational energy to high values of the vibrational counterpart.

Excited hydrogen bonds in the molecular mechanism of muscle contraction.

PubMed

Bespalova, S V; Tolpygo, K B

1991-11-21

The mechanism of muscle contraction is considered. The hydrolysis of an ATP molecule is assumed to produce the excitation of hydrogen bonds A--H...B between electronegative atoms A and B, which are contained in the myosin head and actin filament. This excitation energy epsilon f depends on the interatomic distance AB = R and generates the tractive force f = -delta epsilon f/delta R, that makes atoms AB approach each other. The swing of the myosin head results in macroscopic mutual displacement of actin and myosin polymers. The motion of the actin filament under the action of this force is studied. The conditions under which a considerable portion of the excitation energy converts into the potential tension energy of the actin filament are analysed, and the probability of higher muscle efficiency existence is discussed.

Sinc or Sine? The Band Excitation Method and Energy Dissipation Measurements by SPM

NASA Astrophysics Data System (ADS)

Jesse, Stephen; Kalinin, Sergei

2007-03-01

Quantitative energy dissipation measurements in force-based SPM is the key to understanding fundamental mechanisms of energy transformations on the nanoscale, molecular, and atomic levels. To date, these measurements are invariably based on either phase and amplitude detection in constant frequency mode, or as amplitude detection in frequency-tracking mode. The analysis in both cases implicitly assumes that amplitude is inversely proportional to the Q-factor and is not applicable when the driving force is position dependent, as is the case for virtually all SPM measurements. All current SPM methods sample only a single frequency in the Fourier domain of the system. Thus, only two out of three parameters (amplitude, resonance, and Q) can be determined independently. Here, we developed and implemented a new approach for SPM detection based on the excitation and detection of a signal having a finite amplitude over a selected region in the Fourier domain and allows simultaneous determination of all three parameters. This band excitation method allows acquisition of the local spectral response at a 10ms/pixel rate, compatible with fast imaging, and is illustrated for electromechanical and mechanical imaging and force-distance spectroscopy. The BE method thus represents a new paradigm in SPM, beyond traditional single-frequency excitation.

Isomer depletion as experimental evidence of nuclear excitation by electron capture

NASA Astrophysics Data System (ADS)

Chiara, C. J.; Carroll, J. J.; Carpenter, M. P.; Greene, J. P.; Hartley, D. J.; Janssens, R. V. F.; Lane, G. J.; Marsh, J. C.; Matters, D. A.; Polasik, M.; Rzadkiewicz, J.; Seweryniak, D.; Zhu, S.; Bottoni, S.; Hayes, A. B.; Karamian, S. A.

2018-02-01

The atomic nucleus and its electrons are often thought of as independent systems that are held together in the atom by their mutual attraction. Their interaction, however, leads to other important effects, such as providing an additional decay mode for excited nuclear states, whereby the nucleus releases energy by ejecting an atomic electron instead of by emitting a γ-ray. This ‘internal conversion’ has been known for about a hundred years and can be used to study nuclei and their interaction with their electrons. In the inverse process—nuclear excitation by electron capture (NEEC)—a free electron is captured into an atomic vacancy and can excite the nucleus to a higher-energy state, provided that the kinetic energy of the free electron plus the magnitude of its binding energy once captured matches the nuclear energy difference between the two states. NEEC was predicted in 1976 and has not hitherto been observed. Here we report evidence of NEEC in molybdenum-93 and determine the probability and cross-section for the process in a beam-based experimental scenario. Our results provide a standard for the assessment of theoretical models relevant to NEEC, which predict cross-sections that span many orders of magnitude. The greatest practical effect of the NEEC process may be on the survival of nuclei in stellar environments, in which it could excite isomers (that is, long-lived nuclear states) to shorter-lived states. Such excitations may reduce the abundance of the isotope after its production. This is an example of ‘isomer depletion’, which has been investigated previously through other reactions, but is used here to obtain evidence for NEEC.

Excitation energies of molecules within time-independent density functional theory

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hemanadhan, M., E-mail: hemanadh@iitk.ac.in; Harbola, Manoj K., E-mail: hemanadh@iitk.ac.in

2014-04-24

Recently proposed exchange energy functional for excited-states is tested for obtaining excitation energies of diatomic molecules. The functional is the ground-state counterpart of the local-density approximation, the modified local spin density (MLSD). The MLSD functional is tested for the N{sub 2} and CO diatomic molecules. The excitation energy obtained with the MLSD functional for the N{sub 2} molecule is in close vicinity to that obtained from the exact exchange orbital functional, Krieger, Li and Iafrate (KLI). For the CO molecule, the departure in excitation energy is observed and is due to the overcorrection of self-interaction.

Excitation energies of molecules within time-independent density functional theory

NASA Astrophysics Data System (ADS)

Hemanadhan, M.; Harbola, Manoj K.

2014-04-01

Recently proposed exchange energy functional for excited-states is tested for obtaining excitation energies of diatomic molecules. The functional is the ground-state counterpart of the local-density approximation, the modified local spin density (MLSD). The MLSD functional is tested for the N2 and CO diatomic molecules. The excitation energy obtained with the MLSD functional for the N2 molecule is in close vicinity to that obtained from the exact exchange orbital functional, Krieger, Li and Iafrate (KLI). For the CO molecule, the departure in excitation energy is observed and is due to the overcorrection of self-interaction.

Double Photoionization of excited Lithium and Beryllium

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yip, Frank L.; McCurdy, C. William; Rescigno, Thomas N.

2010-05-20

We present total, energy-sharing and triple differential cross sections for one-photon, double ionization of lithium and beryllium starting from aligned, excited P states. We employ a recently developed hybrid atomic orbital/ numerical grid method based on the finite-element discrete-variable representation and exterior complex scaling. Comparisons with calculated results for the ground-state atoms, as well as analogous results for ground-state and excited helium, serve to highlight important selection rules and show some interesting effects that relate to differences between inter- and intra-shell electron correlation.

Excited atoms in the free-burning Ar arc: treatment of the resonance radiation

NASA Astrophysics Data System (ADS)

Golubovskii, Yu; Kalanov, D.; Gortschakow, S.; Baeva, M.; Uhrlandt, D.

2016-11-01

The collisional-radiative model with an emphasis on the accurate treatment of the resonance radiation transport is developed and applied to the free-burning Ar arc plasma. This model allows for analysis of the influence of resonance radiation on the spatial density profiles of the atoms in different excited states. The comparison of the radial density profiles obtained using an effective transition probability approximation with the results of the accurate solution demonstrates the distinct impact of transport on the profiles and absolute densities of the excited atoms, especially in the arc fringes. The departures from the Saha-Boltzmann equilibrium distributions, caused by different radiative transitions, are analyzed. For the case of the DC arc, the local thermodynamic equilibrium (LTE) state holds close to the arc axis, while strong deviations from the equilibrium state on the periphery occur. In the intermediate radial positions the conditions of partial LTE are fulfilled.

Energy Scaling of Cold Atom-Atom-Ion Three-Body Recombination

NASA Astrophysics Data System (ADS)

Krükow, Artjom; Mohammadi, Amir; Härter, Arne; Denschlag, Johannes Hecker; Pérez-Ríos, Jesús; Greene, Chris H.

2016-05-01

We study three-body recombination of Ba++Rb +Rb in the mK regime where a single 138Ba+ ion in a Paul trap is immersed into a cloud of ultracold 87Rb atoms. We measure the energy dependence of the three-body rate coefficient k3 and compare the results to the theoretical prediction, k3∝Ecol-3 /4, where Ecol is the collision energy. We find agreement if we assume that the nonthermal ion energy distribution is determined by at least two different micromotion induced energy scales. Furthermore, using classical trajectory calculations we predict how the median binding energy of the formed molecules scales with the collision energy. Our studies give new insights into the kinetics of an ion immersed in an ultracold atom cloud and yield important prospects for atom-ion experiments targeting the s -wave regime.

X-alpha calculation of transition energies in multiply ionized atoms

NASA Technical Reports Server (NTRS)

Ringers, D. A.; Chen, M. H.

1974-01-01

It is shown that the accuracy of calculations can be improved if appropriate (different) values of alpha are used for each configuration. Alternatively, the Slater Transition state can be used, wherein a total energy difference is related to a difference in single electron eigenvalues. By a series expansion, the value of alpha for an excited configuration can be related to its value for the ground state configuration. The terms Delta alpha (delta Epsilon/delta alpha) exhibit a similar dependence on atomic number as the ground state values of alpha. Results of sample calculations are reported and compared with experiment.

Excited helium under high pressures in the bulk and in nanobubbles

NASA Astrophysics Data System (ADS)

Pyper, N. C.; Naginey, T. C.; Nellist, P. D.; Whelan, Colm T.

2017-08-01

We systematically investigate the effects of intense pressures on the excitation energies of helium trapped in bubbles in order to deepen our understanding of the fundamental physics of atoms in extreme conditions. The ? excitation energy of a confined helium atom is known to differ from that of a free atom being greater in both the bulk liquid or solid or a bubble confined in a metallic matrix state. We compare calculations for the energy shift with both laboratory experiments for bulk systems and results derived from scanning transmission electron microscope (STEM) studies of helium nanobubbles embedded in different matrices. We find excellent agreement between our calculations and the latest extensive measurements in the bulk. However, we find significant discrepancies when we compare with results deduced using the 'standard' approach for analysing STEM data. Here, we show the scattering matrix element determining the intensity of this excitation in a STEM experiment is significantly affected by the same environmental factors that shift the excitation energy. Consequently, there is a serious theoretical inconsistency in the way the STEM results are calculated, in that the 'standard' approach depends on a supposedly known ? scattering cross section, whereas we show here that this cross section is itself dependent on the environment. Correcting for this inconsistency does not, in itself, improve agreement.

Infrared Auroral Emissions Driven by Resonant Electron Impact Excitation of NO Molecules

NASA Astrophysics Data System (ADS)

Campbell, L.; Brunger, M. J.; Petrovic, Z. Lj.; Jelisavcic, M.; Panajotovic, R.; Buckman, S. J.

2004-05-01

Although only a minor constituent of the earth's upper atmosphere, nitric oxide (NO) plays a major role in infrared auroral emissions due to radiation from vibrationally excited (NO*) states. The main process leading to the production of these excited molecules was thought to be chemiluminescence, whereby excited nitrogen atoms interact with oxygen molecules to form vibrationally excited nitric oxide (NO*) and atomic oxygen. Here we show evidence that a different production mechanism for NO*, due to low energy electron impact excitation of NO molecules, is responsible for more than 30% of the NO auroral emission near 5 μm.

Dissociative Excitation of Acetylene Induced by Electron Impact: Excitation-emission Cross-sections

DOE Office of Scientific and Technical Information (OSTI.GOV)

Országh, Juraj; Danko, Marián; Čechvala, Peter

The optical emission spectrum of acetylene excited by monoenergetic electrons was studied in the range of 190–660 nm. The dissociative excitation and dissociative ionization associated with excitation of the ions initiated by electron impact were dominant processes contributing to the spectrum. The spectrum was dominated by the atomic lines (hydrogen Balmer series, carbon) and molecular bands (CH(A–X), CH(B–X), CH{sup +}(B–A), and C{sub 2}). Besides the discrete transitions, we have detected the continuum emission radiation of ethynyl radical C{sub 2}H(A–X). For most important lines and bands of the spectrum we have measured absolute excitation-emission cross sections and determined the energy thresholdsmore » of the particular dissociative channels.« less

Radiation pressure excitation of a low temperature atomic force/magnetic force microscope for imaging in 4-300 K temperature range

NASA Astrophysics Data System (ADS)

Ćelik, Ümit; Karcı, Özgür; Uysallı, Yiǧit; Özer, H. Özgür; Oral, Ahmet

2017-01-01

We describe a novel radiation pressure based cantilever excitation method for imaging in dynamic mode atomic force microscopy (AFM) for the first time. Piezo-excitation is the most common method for cantilever excitation, however it may cause spurious resonance peaks. Therefore, the direct excitation of the cantilever plays a crucial role in AFM imaging. A fiber optic interferometer with a 1310 nm laser was used both for the excitation of the cantilever at the resonance and the deflection measurement of the cantilever in a commercial low temperature atomic force microscope/magnetic force microscope (AFM/MFM) from NanoMagnetics Instruments. The laser power was modulated at the cantilever's resonance frequency by a digital Phase Locked Loop (PLL). The laser beam is typically modulated by ˜500 μW, and ˜141.8 nmpp oscillation amplitude is obtained in moderate vacuum levels between 4 and 300 K. We have demonstrated the performance of the radiation pressure excitation in AFM/MFM by imaging atomic steps in graphite, magnetic domains in CoPt multilayers between 4 and 300 K and Abrikosov vortex lattice in BSCCO(2212) single crystal at 4 K for the first time.

Radiation pressure excitation of a low temperature atomic force/magnetic force microscope for imaging in 4-300 K temperature range.

PubMed

Çelik, Ümit; Karcı, Özgür; Uysallı, Yiğit; Özer, H Özgür; Oral, Ahmet

2017-01-01

We describe a novel radiation pressure based cantilever excitation method for imaging in dynamic mode atomic force microscopy (AFM) for the first time. Piezo-excitation is the most common method for cantilever excitation, however it may cause spurious resonance peaks. Therefore, the direct excitation of the cantilever plays a crucial role in AFM imaging. A fiber optic interferometer with a 1310 nm laser was used both for the excitation of the cantilever at the resonance and the deflection measurement of the cantilever in a commercial low temperature atomic force microscope/magnetic force microscope (AFM/MFM) from NanoMagnetics Instruments. The laser power was modulated at the cantilever's resonance frequency by a digital Phase Locked Loop (PLL). The laser beam is typically modulated by ∼500 μW, and ∼141.8 nm pp oscillation amplitude is obtained in moderate vacuum levels between 4 and 300 K. We have demonstrated the performance of the radiation pressure excitation in AFM/MFM by imaging atomic steps in graphite, magnetic domains in CoPt multilayers between 4 and 300 K and Abrikosov vortex lattice in BSCCO(2212) single crystal at 4 K for the first time.

A sputtering derived atomic oxygen source for studying fast atom reactions

NASA Technical Reports Server (NTRS)

Ferrieri, Richard A.; Yung, Y. Chu; Wolf, Alfred P.

1987-01-01

A technique for the generation of fast atomic oxygen was developed. These atoms are created by ion beam sputtering from metal oxide surfaces. Mass resolved ion beams at energies up to 60 KeV are produced for this purpose using a 150 cm isotope separator. Studies have shown that particles sputtered with 40 KeV Ar(+) on Ta2O5 were dominantly neutral and exclusively atomic. The atomic oxygen also resided exclusively in its 3P ground state. The translational energy distribution for these atoms peaked at ca 7 eV (the metal-oxygen bond energy). Additional measurements on V2O5 yielded a bimodal distribution with the lower energy peak at ca 5 eV coinciding reasonably well with the metal-oxygen bond energy. The 7 eV source was used to investigate fast oxygen atom reactions with the 2-butene stereoisomers. Relative excitation functions for H-abstraction and pi-bond reaction were measured with trans-2-butene. The abstraction channel, although of minor relative importance at thermal energy, becomes comparable to the addition channel at 0.9 eV and dominates the high-energy regime. Structural effects on the specific channels were also found to be important at high energy.

Vibration-translation energy transfer in vibrationally excited diatomic molecules. Ph.D. Thesis - York Univ., Toronto

NASA Technical Reports Server (NTRS)

Mckenzie, R. L.

1976-01-01

A semiclassical collision model is applied to the study of energy transfer rates between a vibrationally excited diatomic molecule and a structureless atom. The molecule is modeled as an anharmonic oscillator with a multitude of dynamically coupled vibrational states. Three main aspects in the prediction of vibrational energy transfer rates are considered. The applicability of the semiclassical model to an anharmonic oscillator is first evaluated for collinear encounters. Second, the collinear semiclassical model is applied to obtain numerical predictions of the vibrational energy transfer rate dependence on the initial vibrational state quantum number. Thermally averaged vibration-translation rate coefficients are predicted and compared with CO-He experimental values for both ground and excited initial states. The numerical model is also used as a basis for evaluating several less complete but analytic models. Third, the role of rational motion in the dynamics of vibrational energy transfer is examined. A three-dimensional semiclassical collision model is constructed with coupled rotational motion included. Energy transfer within the molecule is shown to be dominated by vibration-rotation transitions with small changes in angular momentum. The rates of vibrational energy transfer in molecules with rational frequencies that are very small in comparison to their vibrational frequency are shown to be adequately treated by the preceding collinear models.

Effects of vacancies on atom displacement threshold energy calculations through Molecular Dynamics Methods in BaTiO3

NASA Astrophysics Data System (ADS)

Gonzalez Lazo, Eduardo; Cruz Inclán, Carlos M.; Rodríguez Rodríguez, Arturo; Guzmán Martínez, Fernando; Abreu Alfonso, Yamiel; Piñera Hernández, Ibrahin; Leyva Fabelo, Antonio

2017-09-01

A primary approach for evaluating the influence of point defects like vacancies on atom displacement threshold energies values Td in BaTiO3 is attempted. For this purpose Molecular Dynamics Methods, MD, were applied based on previous Td calculations on an ideal tetragonal crystalline structure. It is an important issue in achieving more realistic simulations of radiation damage effects in BaTiO3 ceramic materials. It also involves irradiated samples under severe radiation damage effects due to high fluency expositions. In addition to the above mentioned atom displacement events supported by a single primary knock-on atom, PKA, a new mechanism was introduced. It corresponds to the simultaneous excitation of two close primary knock-on atoms in BaTiO3, which might take place under a high flux irradiation. Therefore, two different BaTiO3 Td MD calculation trials were accomplished. Firstly, single PKA excitations in a defective BaTiO3 tetragonal crystalline structure, consisting in a 2×2×2 BaTiO3 perovskite like super cell, were considered. It contains vacancies on Ba and O atomic positions under the requirements of electrical charge balance. Alternatively, double PKA excitations in a perfect BaTiO3 tetragonal unit cell were also simulated. On this basis, the corresponding primary knock-on atom (PKA) defect formation probability functions were calculated at principal crystal directions, and compared with the previous one we calculated and reported at an ideal BaTiO3 tetrahedral crystal structure. As a general result, a diminution of Td values arises in present calculations in comparison with those calculated for single PKA excitation in an ideal BaTiO3 crystal structure.

Matrix photochemistry of small molecules: Influencing reaction dynamics on electronically excited hypersurfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Laursen, S.L.

Investigations of chemical reactions on electronically excited reaction surfaces are presented. The role of excited-surface multiplicity is of particular interest, as are chemical reactivity and energy transfer in systems in which photochemistry is initiated through a metal atom sensitizer.'' Two approaches are employed: A heavy-atom matrix affords access to forbidden triplet reaction surfaces, eliminating the need for a potentially reactive sensitizer. Later, the role of the metal atom in the photosensitization process is examined directly.

Electron impact excitation of tin

NASA Astrophysics Data System (ADS)

Sharma, Lalita; Bharti, Swati; Srivastava, Rajesh

2017-05-01

We study the electron impact excitation of the fine-structure levels of the ground state configuration 5p2 to the excited states of the configuration 5p6s in tin atom. These calculations have been carried out in the jj coupling scheme using the relativistic distorted-wave method. Results for differential cross section are reported at incident electron energies 20, 50, 80 and 100 eV while integrated cross sections are presented in the incident electron energy range of 5 to 100 eV. Contribution to the Topical Issue: "Low-Energy Interactions related to Atmospheric and Extreme Conditions", edited by S. Ptasinska, M. Smialek-Telega, A. Milosavljevic and B. Sivaraman.

Hyperfine structure in 229gTh3+ as a probe of the 229gTh→ 229mTh nuclear excitation energy.

PubMed

Beloy, K

2014-02-14

We identify a potential means to extract the 229gTh→ 229mTh nuclear excitation energy from precision microwave spectroscopy of the 5F(5/2,7/2) hyperfine manifolds in the ion 229gTh3+. The hyperfine interaction mixes this ground fine structure doublet with states of the nuclear isomer, introducing small but observable shifts to the hyperfine sublevels. We demonstrate how accurate atomic structure calculations may be combined with the measurement of the hyperfine intervals to quantify the effects of this mixing. Further knowledge of the magnetic dipole decay rate of the isomer, as recently reported, allows an indirect determination of the nuclear excitation energy.

On optimization of energy harvesting from base-excited vibration

NASA Astrophysics Data System (ADS)

Tai, Wei-Che; Zuo, Lei

2017-12-01

This paper re-examines and clarifies the long-believed optimization conditions of electromagnetic and piezoelectric energy harvesting from base-excited vibration. In terms of electromagnetic energy harvesting, it is typically believed that the maximum power is achieved when the excitation frequency and electrical damping equal the natural frequency and mechanical damping of the mechanical system respectively. We will show that this optimization condition is only valid when the acceleration amplitude of base excitation is constant and an approximation for small mechanical damping when the excitation displacement amplitude is constant. To this end, a two-variable optimization analysis, involving the normalized excitation frequency and electrical damping ratio, is performed to derive the exact optimization condition of each case. When the excitation displacement amplitude is constant, we analytically show that, in contrast to the long-believed optimization condition, the optimal excitation frequency and electrical damping are always larger than the natural frequency and mechanical damping ratio respectively. In particular, when the mechanical damping ratio exceeds a critical value, the optimization condition is no longer valid. Instead, the average power generally increases as the excitation frequency and electrical damping ratio increase. Furthermore, the optimization analysis is extended to consider parasitic electrical losses, which also shows different results when compared with existing literature. When the excitation acceleration amplitude is constant, on the other hand, the exact optimization condition is identical to the long-believed one. In terms of piezoelectric energy harvesting, it is commonly believed that the optimal power efficiency is achieved when the excitation and the short or open circuit frequency of the harvester are equal. Via a similar two-variable optimization analysis, we analytically show that the optimal excitation frequency depends on the

Polarization of Lyman-Alpha Radiation from Atomic Hydrogen Excited by Electron Impact form Near Threshold to 1800 eV

NASA Technical Reports Server (NTRS)

James, G. K.; Slevin, J. A.; Dziczek, D.; McConkey, J. W.; Bray, Igor

1998-01-01

The polarization of Lyman-a radiation, produced by electron-impact excitation of atomic hydrogen, has been measured over the extended energy range from near threshold to 1800 eV. Measurements were obtained in a crossed-beam experiment using a silica-reflection linear polarization analyzer in tandem with a vacuum-ultraviolet monochromator to isolate the emitted line radiation. Comparison with various theoretical calculations shows that the present experimental results are in good agreement with theory over the entire range of electron-impact energies and, in particular, are in excellent agreement with theoretical convergent-close-coupling (CCC) calculations performed in the present work. Our polarization data are significantly different from the previous experimental measurements of Ott, Kauppila, and Fite.

EFFECTS OF LASER RADIATION ON MATTER. LASER PLASMA: Investigation of the populations of excited states of barium atoms in a laser plasma

NASA Astrophysics Data System (ADS)

Burimov, V. N.; Zherikhin, A. N.; Popkov, V. L.

1995-02-01

Laser-induced fluorescence was used in an investigation of the populations of the ground and excited (6s5d 3D1 and 3D2) states of Ba atoms in a plasma formed by laser ablation of Y—Ba—Cu—O target. A nonequilibrium velocity distribution of the atoms was detected. At large distances from the target about 4% of the atoms were in an excited state.

Superradiators created atom by atom

NASA Astrophysics Data System (ADS)

Meschede, Dieter

2018-02-01

High radiation rates are usually associated with macroscopic lasers. Laser radiation is “coherent”—its amplitude and phase are well-defined—but its generation requires energy inputs to overcome loss. Excited atoms spontaneously emit in a random and incoherent fashion, and for N such atoms, the emission rate simply increases as N. However, if these atoms are in close proximity and coherently coupled by a radiation field, this microscopic ensemble acts as a single emitter whose emission rate increases as N2 and becomes “superradiant,” to use Dicke's terminology (1). On page 662 of this issue, Kim et al. (2) show the buildup of coherent light fields through collective emission from atomic radiators injected one by one into a resonator field. There is only one atom ever in the cavity, but the emission is still collective and superradiant. These results suggest another route toward thresholdless lasing.

VUV Study of Electron-Pyrimidine Dissociative Excitation

NASA Astrophysics Data System (ADS)

Hein, Jeff; Al-Khazraji, Hajar; Tiessen, Collin; Lukic, Dragan; Trocchi, Joshuah; McConkey, William

2013-05-01

A crossed electron-gas beam system coupled to a VUV spectrometer has been used to investigate the dissociation of pyrimidine (C4H4N2) into excited atomic fragments in the electron-impact energy range from threshold to 375 eV. Data have been made absolute using Lyman- α from H2 as a secondary standard. The main features in the spectrum are the H Lyman series lines. The emission cross section of Lyman- α is measured to be (2.44 +/- 0.25) 10-18 cm2 at 100 eV impact energy. The probability of extracting C or N atoms from the ring is shown to be very small. Possible dissociation channels and excitation mechanisms in the parent molecule will be discussed. The authors thank NSERC (Canada) for financial support.

The RPA Atomization Energy Puzzle.

PubMed

Ruzsinszky, Adrienn; Perdew, John P; Csonka, Gábor I

2010-01-12

There is current interest in the random phase approximation (RPA), a "fifth-rung" density functional for the exchange-correlation energy. RPA has full exact exchange and constructs the correlation with the help of the unoccupied Kohn-Sham orbitals. In many cases (uniform electron gas, jellium surface, and free atom), the correction to RPA is a short-ranged effect that is captured by a local spin density approximation (LSDA) or a generalized gradient approximation (GGA). Nonempirical density functionals for the correction to RPA were constructed earlier at the LSDA and GGA levels (RPA+), but they are constructed here at the fully nonlocal level (RPA++), using the van der Waals density functional (vdW-DF) of Langreth, Lundqvist, and collaborators. While they make important and helpful corrections to RPA total and ionization energies of free atoms, they correct the RPA atomization energies of molecules by only about 1 kcal/mol. Thus, it is puzzling that RPA atomization energies are, on average, about 10 kcal/mol lower than those of accurate values from experiment. We find here that a hybrid of 50% Perdew-Burke-Ernzerhof GGA with 50% RPA+ yields atomization energies much more accurate than either one does alone. This suggests a solution to the puzzle: While the proper correction to RPA is short-ranged in some systems, its contribution to the correlation hole can spread out in a molecule with multiple atomic centers, canceling part of the spread of the exact exchange hole (more so than in RPA or RPA+), making the true exchange-correlation hole more localized than in RPA or RPA+. This effect is not captured even by the vdW-DF nonlocality, but it requires the different kind of full nonlocality present in a hybrid functional.

Contact resonance atomic force microscopy imaging in air and water using photothermal excitation.

PubMed

Kocun, Marta; Labuda, Aleksander; Gannepalli, Anil; Proksch, Roger

2015-08-01

Contact Resonance Force Microscopy (CR-FM) is a leading atomic force microscopy technique for measuring viscoelastic nano-mechanical properties. Conventional piezo-excited CR-FM measurements have been limited to imaging in air, since the "forest of peaks" frequency response associated with acoustic excitation methods effectively masks the true cantilever resonance. Using photothermal excitation results in clean contact, resonance spectra that closely match the ideal frequency response of the cantilever, allowing unambiguous and simple resonance frequency and quality factor measurements in air and liquids alike. This extends the capabilities of CR-FM to biologically relevant and other soft samples in liquid environments. We demonstrate CR-FM in air and water on both stiff silicon/titanium samples and softer polystyrene-polyethylene-polypropylene polymer samples with the quantitative moduli having very good agreement between expected and measured values.

High temperature electronic excitation and ionization rates in gases

NASA Technical Reports Server (NTRS)

Hansen, Frederick

1991-01-01

The relaxation times for electronic excitation due to electron bombardment of atoms was found to be quite short, so that electron kinetic temperature (T sub e) and the electron excitation temperature (T asterisk) should equilibrate quickly whenever electrons are present. However, once equilibrium has been achieved, further energy to the excited electronic states and to the kinetic energy of free electrons must be fed in by collisions with heavy particles that cause vibrational and electronic state transitions. The rate coefficients for excitation of electronic states produced by heavy particle collision have not been well known. However, a relatively simple semi-classical theory has been developed here which is analytic up to the final integration over a Boltzmann distribution of collision energies; this integral can then be evaluated numerically by quadrature. Once the rate coefficients have been determined, the relaxation of electronic excitation energy can be evaluated and compared with the relaxation rates of vibrational excitation. Then the relative importance of these two factors, electronic excitation and vibrational excitation by heavy particle collision, on the transfer of energy to free electron motion, can be assessed.

Spatial Imaging of Strongly Interacting Rydberg Atoms

NASA Astrophysics Data System (ADS)

Thaicharoen, Nithiwadee

The strong interactions between Rydberg excitations can result in spatial correlations between the excitations. The ability to control the interaction strength and the correlations between Rydberg atoms is applicable in future technological implementations of quantum computation. In this thesis, I investigates how both the character of the Rydberg-Rydberg interactions and the details of the excitation process affect the nature of the spatial correlations and the evolution of those correlations in time. I first describes the experimental apparatus and methods used to perform high-magnification Rydberg-atom imaging, as well as three experiments in which these methods play an important role. The obtained Rydberg-atom positions reveal the correlations in the many-body Rydberg-atom system and their time dependence with sub-micron spatial resolution. In the first experiment, atoms are excited to a Rydberg state that experiences a repulsive van der Waals interaction. The Rydberg excitations are prepared with a well-defined initial separation, and the effect of van der Waals forces is observed by tracking the interatomic distance between the Rydberg atoms. The atom trajectories and thereby the interaction coefficient C6 are extracted from the pair correlation functions of the Rydberg atom positions. In the second experiment, the Rydberg atoms are prepared in a highly dipolar state by using adiabatic state transformation. The atom-pair kinetics that follow from the strong dipole-dipole interactions are observed. The pair correlation results provide the first direct visualization of the electric-dipole interaction and clearly exhibit its anisotropic nature. In both the first and the second experiment, results of semi-classical simulations of the atom-pair trajectories agree well with the experimental data. In the analysis, I use energy conservation and measurements of the initial positions and the terminal velocities of the atom pairs to extract the C6 and C 3 interaction

Imaging Spatial Correlations of Rydberg Excitations in Cold Atom Clouds

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schwarzkopf, A.; Sapiro, R. E.; Raithel, G.

2011-09-02

We use direct spatial imaging of cold {sup 85}Rb Rydberg atom clouds to measure the Rydberg-Rydberg correlation function. The results are in qualitative agreement with theoretical predictions [F. Robicheaux and J. V. Hernandez, Phys. Rev. A 72, 063403 (2005)]. We determine the blockade radius for states 44D{sub 5/2}, 60D{sub 5/2}, and 70D{sub 5/2} and investigate the dependence of the correlation behavior on excitation conditions and detection delay. Experimental data hint at the existence of long-range order.

A History of the Atomic Energy Commission

DOE R&D Accomplishments Database

Buck, Alice L.

1983-07-01

This pamphlet traces the history of the US Atomic Energy Commission's twenty-eight year stewardship of the Nation's nuclear energy program, from the signing of the Atomic Energy Act on August 1, 1946 to the signing of the Energy Reorganization Act on October 11, 1974. The Commission's early concentration on the military atom produced sophisticated nuclear weapons for the Nation's defense and made possible the creation of a fleet of nuclear submarines and surface ships. Extensive research in the nuclear sciences resulted in the widespread application of nuclear technology for scientific, medical and industrial purposes, while the passage of the Atomic Energy Act of 1954 made possible the development of a nuclear industry, and enabled the United States to share the new technology with other nations.

Electron impact excitation of higher energy states of molecular oxygen in the atmosphere of Europa

NASA Astrophysics Data System (ADS)

Campbell, L.; Tanaka, H.; Kato, H.; Jayaraman, S.; Brunger, M. J.

2012-01-01

Recent measurements of integral cross sections for electron impact excitation of the Schumann-Runge continuum, longest band and second band of molecular oxygen are applied to calculations of emissions from the atmosphere of Europa. Molecules excited to these bands predissociate, producing O(1D) (excited oxygen) atoms which subsequently decay to produce 630.0-nm radiation. Radiation of this wavelength is also produced by direct excitation of O atoms and by the recombination of O _2^+ + 2 with electrons, but these two processes also produce O(1S) atoms which then emit at 557.7 nm. It is shown by modeling that the ratio of 630.0-nm to 557.7-nm is sensitive to the relative importance of the three processes, suggesting that the ratio would be a useful remote sensing probe in the atmosphere of Europa. In particular, the excitation of the Schumann-Runge continuum, longest band and second band is produced by magnetospheric electrons while the recombination is produced by secondary electrons produced in the atmosphere. This difference raises the possibility of determination of the secondary electron spectrum by measurement of light emissions.

Plasmon-induced nonlinear response of silver atomic chains.

PubMed

Yan, Lei; Guan, Mengxue; Meng, Sheng

2018-05-10

Nonlinear response of a linear silver atomic chain upon ultrafast laser excitation has been studied in real time using the time-dependent density functional theory. We observe the presence of nonlinear responses up to the fifth order in tunneling current, which is ascribed to the excitation of high-energy electrons generated by Landau damping of plasmons. The nonlinear effect is enhanced after adsorption of polar molecules such as water due to the enhanced damping rates during plasmon decay. Increasing the length of atomic chains also increases the nonlinear response, favoring higher-order plasmon excitation. These findings offer new insights towards a complete understanding and ultimate control of plasmon-induced nonlinear phenomena to atomic precision.

Quantum scattering calculations for ro-vibrational de-excitation of CO by hydrogen atoms

DOE Office of Scientific and Technical Information (OSTI.GOV)

Song, Lei; Avoird, Ad van der; Karman, Tijs

2015-05-28

We present quantum-mechanical scattering calculations for ro-vibrational relaxation of carbon monoxide (CO) in collision with hydrogen atoms. Collisional cross sections of CO ro-vibrational transitions from v = 1, j = 0 − 30 to v′ = 0, j′ are calculated using the close coupling method for collision energies between 0.1 and 15 000 cm{sup −1} based on the three-dimensional potential energy surface of Song et al. [J. Phys. Chem. A 117, 7571 (2013)]. Cross sections of transitions from v = 1, j ≥ 3 to v′ = 0, j′ are reported for the first time at this level of theory. Alsomore » calculations by the more approximate coupled states and infinite order sudden (IOS) methods are performed in order to test the applicability of these methods to H–CO ro-vibrational inelastic scattering. Vibrational de-excitation rate coefficients of CO (v = 1) are presented for the temperature range from 100 K to 3000 K and are compared with the available experimental and theoretical data. All of these results and additional rate coefficients reported in a forthcoming paper are important for including the effects of H–CO collisions in astrophysical models.« less

[Study of characteristics of excited O atom generated in multi-needle-to-plate corona discharge by emission spectroscopy].

PubMed

Ge, Hui; Yan, Ling; Mi, Dong; Zhu, Yi-min; Zhang, Lu

2012-04-01

The emission spectra of O(3p 5 P --> 3s 5 S2(0) 777.4 nm) produced by multi-needle-to-plate negative corona discharge and positive streamer discharge in air were successfully recorded at one atmosphere. The influences of discharge power, electrode gap, content of N2 and relative humidity on the excited O atom production were investigated in negative corona discharge. Meanwhile, the distribution of relative density of excited O atom in discharge space was also studied in positive streamer discharge. The results indicate that, for negative corona discharge, the amount of O active atom increases with the increase in power, decreases with increased discharge gap. And with the increase in relative humidity and N2 content, its amount firstly increases and then decreases; whereas for positive corona discharge, the relative density of O active atom from needlepoint to plate firstly increases and then decreases.

Energetic Metastable Oxygen and Nitrogen Atoms in the Terrestrial Atmosphere

NASA Technical Reports Server (NTRS)

Kharchenko, Vasili

2003-01-01

We have investigated the energy distributions of the metastable oxygen atoms in the terrestrial thermosphere. Nascent O(lD) atoms play a fundamental role in the energy balance and chemistry of the terrestrial atmosphere, because they are produced by photo-chemical reactions in the excited electronic states and carry significant translational energies.

Behavior of Excited Argon Atoms in Inductively Driven Plasmas

DOE Office of Scientific and Technical Information (OSTI.GOV)

HEBNER,GREGORY A.; MILLER,PAUL A.

1999-12-07

Laser induced fluorescence has been used to measure the spatial distribution of the two lowest energy argon excited states, 1s{sub 5} and 1s{sub 4}, in inductively driven plasmas containing argon, chlorine and boron trichloride. The behavior of the two energy levels with plasma conditions was significantly different, probably because the 1s{sub 5} level is metastable and the 1s{sub 4} level is radiatively coupled to the ground state but is radiation trapped. The argon data is compared with a global model to identify the relative importance of processes such as electron collisional mixing and radiation trapping. The trends in the datamore » suggest that both processes play a major role in determining the excited state density. At lower rfpower and pressure, excited state spatial distributions in pure argon were peaked in the center of the discharge, with an approximately Gaussian profile. However, for the highest rfpowers and pressures investigated, the spatial distributions tended to flatten in the center of the discharge while the density at the edge of the discharge was unaffected. The spatially resolved excited state density measurements were combined with previous line integrated measurements in the same discharge geometry to derive spatially resolved, absolute densities of the 1s{sub 5} and 1s{sub 4} argon excited states and gas temperature spatial distributions. Fluorescence lifetime was a strong fi.mction of the rf power, pressure, argon fraction and spatial location. Increasing the power or pressure resulted in a factor of two decrease in the fluorescence lifetime while adding Cl{sub 2} or BCl{sub 3} increased the fluorescence lifetime. Excited state quenching rates are derived from the data. When Cl{sub 2} or BCl{sub 3} was added to the plasma, the maximum argon metastable density depended on the gas and ratio. When chlorine was added to the argon plasma, the spatial density profiles were independent of chlorine fraction. While it is energetically

Probing the Quantum States of a Single Atom Transistor at Microwave Frequencies.

PubMed

Tettamanzi, Giuseppe Carlo; Hile, Samuel James; House, Matthew Gregory; Fuechsle, Martin; Rogge, Sven; Simmons, Michelle Y

2017-03-28

The ability to apply gigahertz frequencies to control the quantum state of a single P atom is an essential requirement for the fast gate pulsing needed for qubit control in donor-based silicon quantum computation. Here, we demonstrate this with nanosecond accuracy in an all epitaxial single atom transistor by applying excitation signals at frequencies up to ≈13 GHz to heavily phosphorus-doped silicon leads. These measurements allow the differentiation between the excited states of the single atom and the density of states in the one-dimensional leads. Our pulse spectroscopy experiments confirm the presence of an excited state at an energy ≈9 meV, consistent with the first excited state of a single P donor in silicon. The relaxation rate of this first excited state to the ground state is estimated to be larger than 2.5 GHz, consistent with theoretical predictions. These results represent a systematic investigation of how an atomically precise single atom transistor device behaves under radio frequency excitations.

Regulating energy transfer of excited carriers and the case for excitation-induced hydrogen dissociation on hydrogenated graphene

PubMed Central

Bang, Junhyeok; Meng, Sheng; Sun, Yi-Yang; West, Damien; Wang, Zhiguo; Gao, Fei; Zhang, S. B.

2013-01-01

Understanding and controlling of excited carrier dynamics is of fundamental and practical importance, particularly in photochemistry and solar energy applications. However, theory of energy relaxation of excited carriers is still in its early stage. Here, using ab initio molecular dynamics (MD) coupled with time-dependent density functional theory, we show a coverage-dependent energy transfer of photoexcited carriers in hydrogenated graphene, giving rise to distinctively different ion dynamics. Graphene with sparsely populated H is difficult to dissociate due to inefficient transfer of the excitation energy into kinetic energy of the H. In contrast, H can easily desorb from fully hydrogenated graphane. The key is to bring down the H antibonding state to the conduction band minimum as the band gap increases. These results can be contrasted to those of standard ground-state MD that predict H in the sparse case should be much less stable than that in fully hydrogenated graphane. Our findings thus signify the importance of carrying out explicit electronic dynamics in excited-state simulations. PMID:23277576

Goldstone mode and pair-breaking excitations in atomic Fermi superfluids

NASA Astrophysics Data System (ADS)

Hoinka, Sascha; Dyke, Paul; Lingham, Marcus G.; Kinnunen, Jami J.; Bruun, Georg M.; Vale, Chris J.

2017-10-01

Spontaneous symmetry breaking is a central paradigm of elementary particle physics, magnetism, superfluidity and superconductivity. According to Goldstone's theorem, phase transitions that break continuous symmetries lead to the existence of gapless excitations in the long-wavelength limit. These Goldstone modes can become the dominant low-energy excitation, showing that symmetry breaking has a profound impact on the physical properties of matter. Here, we present a comprehensive study of the elementary excitations in a homogeneous strongly interacting Fermi gas through the crossover from a Bardeen-Cooper-Schrieffer (BCS) superfluid to a Bose-Einstein condensate (BEC) of molecules using two-photon Bragg spectroscopy. The spectra exhibit a discrete Goldstone mode, associated with the broken-symmetry superfluid phase, as well as pair-breaking single-particle excitations. Our techniques yield a direct determination of the superfluid pairing gap and speed of sound in close agreement with strong-coupling theories.

Contact resonance atomic force microscopy imaging in air and water using photothermal excitation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kocun, Marta; Labuda, Aleksander; Gannepalli, Anil

2015-08-15

Contact Resonance Force Microscopy (CR-FM) is a leading atomic force microscopy technique for measuring viscoelastic nano-mechanical properties. Conventional piezo-excited CR-FM measurements have been limited to imaging in air, since the “forest of peaks” frequency response associated with acoustic excitation methods effectively masks the true cantilever resonance. Using photothermal excitation results in clean contact, resonance spectra that closely match the ideal frequency response of the cantilever, allowing unambiguous and simple resonance frequency and quality factor measurements in air and liquids alike. This extends the capabilities of CR-FM to biologically relevant and other soft samples in liquid environments. We demonstrate CR-FM inmore » air and water on both stiff silicon/titanium samples and softer polystyrene-polyethylene-polypropylene polymer samples with the quantitative moduli having very good agreement between expected and measured values.« less

Positron-alkali atom scattering

NASA Technical Reports Server (NTRS)

Mceachran, R. P.; Horbatsch, M.; Stauffer, A. D.; Ward, S. J.

1990-01-01

Positron-alkali atom scattering was recently investigated both theoretically and experimentally in the energy range from a few eV up to 100 eV. On the theoretical side calculations of the integrated elastic and excitation cross sections as well as total cross sections for Li, Na and K were based upon either the close-coupling method or the modified Glauber approximation. These theoretical results are in good agreement with experimental measurements of the total cross section for both Na and K. Resonance structures were also found in the L = 0, 1 and 2 partial waves for positron scattering from the alkalis. The structure of these resonances appears to be quite complex and, as expected, they occur in conjunction with the atomic excitation thresholds. Currently both theoretical and experimental work is in progress on positron-Rb scattering in the same energy range.

Partitioning dynamic electron correlation energy: Viewing Møller-Plesset correlation energies through Interacting Quantum Atom (IQA) energy partitioning

NASA Astrophysics Data System (ADS)

McDonagh, James L.; Vincent, Mark A.; Popelier, Paul L. A.

2016-10-01

Here MP2, MP3 and MP4(SDQ) are energy-partitioned for the first time within the Interacting Quantum Atoms (IQA) context, as proof-of-concept for H2, He2 and HF. Energies are decomposed into four primary energy contributions: (i) atomic self-energies, and atomic interaction energies comprising of (ii) Coulomb, (iii) exchange and (iv) dynamic election correlation terms. We generate and partition one- and two-particle density-matrices to obtain all atomic energy components. This work suggests that, in terms of Van der Waals dispersion, the correlation energies represent an atomic stabilisation, by proximity to other atoms, as opposed to direct interactions with other nearby atoms.

Dissociation dynamics of simple chlorine containing molecules upon resonant Cl K-σ{sup *} excitation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bohinc, R., E-mail: rok.bohinc@ijs.si; Bučar, K.; Kavčič, M.

2014-04-28

A theoretical analysis of dissociation dynamics of chlorine K-σ{sup *} core-excited molecules is performed. The potential energy surfaces of HCl, Cl{sub 2}, CH{sub 3}Cl, CH{sub 2}Cl{sub 2}, CHCl{sub 3}, CCl{sub 4}, CFCl{sub 3}, CF{sub 2}Cl{sub 2}, and CF{sub 3}Cl are calculated along the normal vibrational modes of the ground electronic state yielding the widths of the corresponding Franck-Condon distributions. An insight into the potential energy surface of 1st σ{sup *} resonances shows that the initial dissociation dynamics of chloro(fluoro)methanes mainly involves the distancing of the carbon and the core-excited chlorine atom and is practically independent of other atoms in themore » molecule, which is in agreement with the recent experimental findings. The carbon atom pulls out the remaining three atoms shortly after piercing the three-atom plane resulting in a high vibrationally excited state of the fragment if the reconnection time is smaller than the lifetime of the L shell.« less

Nested variant of the method of moments of coupled cluster equations for vertical excitation energies and excited-state potential energy surfaces.

PubMed

Kowalski, Karol

2009-05-21

In this article we discuss the problem of proper balancing of the noniterative corrections to the ground- and excited-state energies obtained with approximate coupled cluster (CC) and equation-of-motion CC (EOMCC) approaches. It is demonstrated that for a class of excited states dominated by single excitations and for states with medium doubly excited component, the newly introduced nested variant of the method of moments of CC equations provides mathematically rigorous way of balancing the ground- and excited-state correlation effects. The resulting noniterative methodology accounting for the effect of triples is tested using its parallel implementation on the systems, for which iterative CC/EOMCC calculations with full inclusion of triply excited configurations or their most important subset are numerically feasible.

Observation of correlated excitations in bimolecular collisions

NASA Astrophysics Data System (ADS)

Gao, Zhi; Karman, Tijs; Vogels, Sjoerd N.; Besemer, Matthieu; van der Avoird, Ad; Groenenboom, Gerrit C.; van de Meerakker, Sebastiaan Y. T.

2018-02-01

Although collisions between atoms and molecules are largely understood, collisions between two molecules have proven much harder to study. In both experiment and theory, our ability to determine quantum-state-resolved bimolecular cross-sections lags behind their atom-molecule counterparts by decades. For many bimolecular systems, even rules of thumb—much less intuitive understanding—of scattering cross sections are lacking. Here, we report the measurement of state-to-state differential cross sections on the collision of state-selected and velocity-controlled nitric oxide (NO) radicals and oxygen (O2) molecules. Using velocity map imaging of the scattered NO radicals, the full product-pair correlations of rotational excitation that occurs in both collision partners from individual encounters are revealed. The correlated cross sections show surprisingly good agreement with quantum scattering calculations using ab initio NO-O2 potential energy surfaces. The observations show that the well-known energy-gap law that governs atom-molecule collisions does not generally apply to bimolecular excitation processes, and reveal a propensity rule for the vector correlation of product angular momenta.

Singly and Doubly Excited States of the D-Dimensional Helium Atom(Supported by DOD-ONR N00014-94-1-0998)

NASA Astrophysics Data System (ADS)

Carzoli, J.; Dunn, M.; Watson, D. K.

1998-05-01

Large order dimensional perturbation theory (DPT) has been used to study the ground and a number of excited states of two-electron atoms for the case L=0. Here we present the first application of recent work generalizing DPT to higher angular momentum.(M. Dunn, D.K. Watson, Ann. Phys. 251 (1996) 266)^,(M. Dunn, D.K. Watson, The Large Dimension Limit of Higher Angular Momentum States. Phys. Rev. A. (accepted for publication)) In this work we begin the investigation of P^o states, presenting results for the energies of some of the lowest lying states and discuss the analytic structure of these energies as functions of 1/D. We also obtain energies of corresponding D^o states with almost no additional effort by making use of interdimensional degeneracies with the P^o states.

Level density parameter behaviour at high excitation energy

NASA Astrophysics Data System (ADS)

D'Arrigo, A.; Giardina, G.; Taccone, A.

1991-06-01

We present a formalism to calculate the intrinsic (without collective effects) and effective (with collective effects) level density parameters over a wide range of excitation energy up to 180 MeV. The behaviour of aint and aeff as an energy function is shown for several typical nuclei (115Cd, 129Te, 148Pm, 173Yb, 192Ir and 248Cm). Moreover, local systematics of the parameter aeff as a function of the neutron number N, also for nuclei extremely far from the β-line, is shown for some typical nuclei (Rb, Pd, Sn, Ba and Hg) at excitation energies of 15, 80 and 150 MeV.

Line Profile of H Lyman (alpha) from Dissociative Excitation of H2 with Application to Jupiter

NASA Technical Reports Server (NTRS)

Ajello, Joseph M.; Kasnik, Isik; Ahmed, Syed M.; Clarke, John T.

1995-01-01

Observations of the H Lyman(alpha) (Ly-alpha) emission from Jupiter have shown pronounced emissions, exceeding solar fluorescence, in the polar aurora and equatorial "bulge" regions. The H Ly-alpha line profiles from these regions are broader than expected, indicating high-energy processes producing fast atoms as determined from the observed Doppler broadening. Toward understanding that process a high-resolution ultraviolet (UV) spectrometer was employed for the first measurement of the H Ly-alpha emission Doppler profile from dissociative excitation of H2 by electron impact. Analysis of the deconvolved line profile reveals the existence of a narrow central peak of 40 +/- 4 mA full width at half maximum and a broad pedestal base about 240 mA wide. Two distinct dissociation mechanisms account for this Doppler structure. Slow H(2p) atoms characterized by a distribution function with peak energy near 80 meV produce the peak profile, which is nearly independent of the electron impact energy. Slow H(2p) atoms arise from direct dissociation and predissociation of singly excited states which have a dissociation limit of 14.68 eV. The wings of H Ly-alpha arise from dissociative excitation of a series of doubly excited states which cross the Franck-Condon region between 23 and 40 eV. The profile of the wings is dependent on the electron impact energy, and the distribution function of fast H(2p) atoms is therefore dependent on the electron impact energy. The fast atom kinetic energy distribution at 100 eV electron impact energy spans the energy range from 1 to 10 eV with a peak near 4 eV. For impact energies above 23 eV the fast atoms contribute to a slightly asymmetric structure of the line profile. The absolute cross sections of the H Ly-alpha line peak and wings were measured over the range from 0 to 200 eV. Analytic model coefficients are given for the measured cross sections which can be applied to planetary atmosphere auroral and dayglow calculations. The dissociative

Electron transfer, ionization, and excitation in atomic collisions. Progress report, June 15, 1992--June 14, 1995

DOE Office of Scientific and Technical Information (OSTI.GOV)

Winter, T.G.; Alston, S.G.

The research program of Winter and Alston addresses the fundamental processes of electron transfer, ionization, and excitation in ion-atom, ion-ion, and ion-molecule collisions. Attention is focussed on one- and two-electron systems and, more recently, quasi-one-electron systems whose electron-target-core interaction can be accurately modeled by one-electron potentials. The basic computational approaches can then be taken with few, if any, approximations, and the underlying collisional mechanisms can be more clearly revealed. Winter has focussed on intermediate collision energies (e.g., proton energies for p-He{sup +} collisions on the order of 100 kilo-electron volts), in which many electron states are strongly coupled during themore » collision and a coupled-state approach, such as a coupled-Sturmian-pseudostate approach, is appropriate. Alston has concentrated on higher collision energies (million electron-volt energies), or asymmetric collision systems, for which the coupling of the projectile is weaker with, however, many more target states being coupled together so that high-order perturbation theory is essential. Several calculations by Winter and Alston are described, as set forth in the original proposal.« less

Ion-neutral chemistry at ultralow energies: dynamics of reactive collisions between laser-cooled Ca+ ions and Rb atoms in an ion-atom hybrid trap†

NASA Astrophysics Data System (ADS)

Hall, Felix H. J.; Eberle, Pascal; Hegi, Gregor; Raoult, Maurice; Aymar, Mireille; Dulieu, Olivier; Willitsch, Stefan

2013-08-01

Cold chemical reactions between laser-cooled Ca+ ions and Rb atoms were studied in an ion-atom hybrid trap. Reaction rate constants were determined in the range of collision energies ⟨E coll⟩/k B=20 mK-20 K. The lowest energies were achieved in experiments using single localised Ca+ ions. Product branching ratios were studied using resonant-excitation mass spectrometry. The dynamics of the reactive processes in this system (non-radiative and radiative charge transfer as well as radiative association leading to the formation of CaRb+ molecular ions) have been analysed using high-level quantum-chemical calculations of the potential energy curves of CaRb+ and quantum-scattering calculations for the radiative channels. For the present low-energy scattering experiments, it is shown that the energy dependence of the reaction rate constants is governed by long-range interactions in line with the classical Langevin model, but their magnitude is determined by short-range non-adiabatic and radiative couplings which only weakly depend on the asymptotic energy. The quantum character of the collisions is predicted to manifest itself in the occurrence of narrow shape resonances at well-defined collision energies. The present results highlight both universal and system-specific phenomena in cold ion-neutral reactive collisions.

Excitation energies from particle-particle random phase approximation with accurate optimized effective potentials

NASA Astrophysics Data System (ADS)

Jin, Ye; Yang, Yang; Zhang, Du; Peng, Degao; Yang, Weitao

2017-10-01

The optimized effective potential (OEP) that gives accurate Kohn-Sham (KS) orbitals and orbital energies can be obtained from a given reference electron density. These OEP-KS orbitals and orbital energies are used here for calculating electronic excited states with the particle-particle random phase approximation (pp-RPA). Our calculations allow the examination of pp-RPA excitation energies with the exact KS density functional theory (DFT). Various input densities are investigated. Specifically, the excitation energies using the OEP with the electron densities from the coupled-cluster singles and doubles method display the lowest mean absolute error from the reference data for the low-lying excited states. This study probes into the theoretical limit of the pp-RPA excitation energies with the exact KS-DFT orbitals and orbital energies. We believe that higher-order correlation contributions beyond the pp-RPA bare Coulomb kernel are needed in order to achieve even higher accuracy in excitation energy calculations.

Heavy atom vibrational modes and low-energy vibrational autodetachment in nitromethane anions

NASA Astrophysics Data System (ADS)

Thompson, Michael C.; Baraban, Joshua H.; Matthews, Devin A.; Stanton, John F.; Weber, J. Mathias

2015-06-01

We report infrared spectra of nitromethane anion, CH3NO2-, in the region 700-2150 cm-1, obtained by Ar predissociation spectroscopy and electron detachment spectroscopy. The data are interpreted in the framework of second-order vibrational perturbation theory based on coupled-cluster electronic structure calculations. The modes in the spectroscopic region studied here are mainly based on vibrations involving the heavier atoms; this work complements earlier studies on nitromethane anion that focused on the CH stretching region of the spectrum. Electron detachment begins at photon energies far below the adiabatic electron affinity due to thermal population of excited vibrational states.

Heavy atom vibrational modes and low-energy vibrational autodetachment in nitromethane anions.

PubMed

Thompson, Michael C; Baraban, Joshua H; Matthews, Devin A; Stanton, John F; Weber, J Mathias

2015-06-21

We report infrared spectra of nitromethane anion, CH3NO2 (-), in the region 700-2150 cm(-1), obtained by Ar predissociation spectroscopy and electron detachment spectroscopy. The data are interpreted in the framework of second-order vibrational perturbation theory based on coupled-cluster electronic structure calculations. The modes in the spectroscopic region studied here are mainly based on vibrations involving the heavier atoms; this work complements earlier studies on nitromethane anion that focused on the CH stretching region of the spectrum. Electron detachment begins at photon energies far below the adiabatic electron affinity due to thermal population of excited vibrational states.

The H + OCS hot atom reaction - CO state distributions and translational energy from time-resolved infrared absorption spectroscopy

NASA Technical Reports Server (NTRS)

Nickolaisen, Scott L.; Cartland, Harry E.

1993-01-01

Time-resolved infrared diode laser spectroscopy has been used to probe CO internal and translational excitation from the reaction of hot H atoms with OCS. Product distributions should be strongly biased toward the maximum 1.4 eV collision energy obtained from 278 nm pulsed photolysis of HI. Rotations and vibrations are both colder than predicted by statistical density of states theory, as evidenced by large positive surprisal parameters. The bias against rotation is stronger than that against vibration, with measurable population as high as v = 4. The average CO internal excitation is 1920/cm, accounting for only 13 percent of the available energy. Of the energy balance, time-resolved sub-Doppler line shape measurements show that more than 38 percent appears as relative translation of the separating CO and SH fragments. Studies of the relaxation kinetics indicate that some rotational energy transfer occurs on the time scale of our measurements, but the distributions do not relax sufficiently to alter our conclusions. Vibrational distributions are nascent, though vibrational relaxation of excited CO is unusually fast in the OCS bath, with rates approaching 3 percent of gas kinetic for v = 1.

Interactions and low-energy collisions between an alkali ion and an alkali atom of a different nucleus

NASA Astrophysics Data System (ADS)

Rakshit, Arpita; Ghanmi, Chedli; Berriche, Hamid; Deb, Bimalendu

2016-05-01

We study theoretically interaction potentials and low-energy collisions between different alkali atoms and alkali ions. Specifically, we consider systems such as X + {{{Y}}}+, where X({{{Y}}}+) is either Li(Cs+) or Cs(Li+), Na(Cs+) or Cs(Na+) and Li(Rb+) or Rb(Li+). We calculate the molecular potentials of the ground and first two excited states of these three systems using a pseudopotential method and compare our results with those obtained by others. We derive ground-state scattering wave functions and analyze the cold collisional properties of these systems for a wide range of energies. We find that, in order to get convergent results for the total scattering cross sections for energies of the order 1 K, one needs to take into account at least 60 partial waves. The low-energy scattering properties calculated in this paper may serve as a precursor for experimental exploration of quantum collisions between an alkali atom and an alkali ion of a different nucleus.

Energy from the Atom.

ERIC Educational Resources Information Center

Smith, Patricia L.

This curriculum guide was written to supplement fifth and sixth grade science units on matter and energy. It was designed to provide more in-depth material on the atom. The first part, "Teacher Guide," contains background information, biographical sketches of persons in the history of nuclear energy, vocabulary, answer sheets, management sheets…

78 FR 64414 - Assistance to Foreign Atomic Energy Activities

Federal Register 2010, 2011, 2012, 2013, 2014

2013-10-29

... DEPARTMENT OF ENERGY 10 CFR Part 810 RIN 1994-AA02 Assistance to Foreign Atomic Energy Activities... Assistance to Foreign Atomic Energy Activities since 1986. The NOPR reflected a need to make the regulations... concerning Assistance to Foreign Atomic Energy Activities since 1986. (76 FR 55278) The NOPR reflected a need...

Electron-lattice energy relaxation in laser-excited thin-film Au-insulator heterostructures studied by ultrafast MeV electron diffraction.

PubMed

Sokolowski-Tinten, K; Shen, X; Zheng, Q; Chase, T; Coffee, R; Jerman, M; Li, R K; Ligges, M; Makasyuk, I; Mo, M; Reid, A H; Rethfeld, B; Vecchione, T; Weathersby, S P; Dürr, H A; Wang, X J

2017-09-01

We apply time-resolved MeV electron diffraction to study the electron-lattice energy relaxation in thin film Au-insulator heterostructures. Through precise measurements of the transient Debye-Waller-factor, the mean-square atomic displacement is directly determined, which allows to quantitatively follow the temporal evolution of the lattice temperature after short pulse laser excitation. Data obtained over an extended range of laser fluences reveal an increased relaxation rate when the film thickness is reduced or the Au-film is capped with an additional insulator top-layer. This behavior is attributed to a cross-interfacial coupling of excited electrons in the Au film to phonons in the adjacent insulator layer(s). Analysis of the data using the two-temperature-model taking explicitly into account the additional energy loss at the interface(s) allows to deduce the relative strength of the two relaxation channels.

Electron-impact ionization of atomic hydrogen at incident electron energies of 15.6, 17.6, 25, and 40 eV

DOE Office of Scientific and Technical Information (OSTI.GOV)

Childers, J. G.; James, K. E.; Hughes, M.

2003-09-01

Absolute doubly differential cross sections for the electron-impact ionization of atomic hydrogen have been measured from near threshold to intermediate energies. The measurements are calibrated to the well-established, accurate differential cross section for electron-impact excitation of the atomic hydrogen transition H(1{sup 2}S{yields}2{sup 2}S+2{sup 2}P). In these experiments background secondary electrons are suppressed by moving the atomic hydrogen target source to and from the collision region. Measurements cover the incident electron energy range of 14.6-40 eV, for scattering angles of 10 degree sign -120 degree sign and are found to be in very good agreement with the results of the mostmore » advanced theoretical models--the convergent close-coupling model and the exterior complex scaling model.« less

Ion-neutral chemistry at ultralow energies:Dynamics of reactive collisions between laser-cooled Ca+ or Ba+ ions and Rb atoms in an ion-atom hybrid trap

NASA Astrophysics Data System (ADS)

Dulieu, O.; Hall, F. H. J.; Eberle, P.; Hegi, G.; Raoult, M.; Aymar, M.; Willitsch, S.

2013-05-01

Cold chemical reactions between laser-cooled Ca+ or Ba+ ions and Rb atoms were studied in an ion-atom hybrid trap. Reaction rate constants were determined in the collision energy range Ecoll /kB = 20 mK-20 K. Product branching ratios were studied using resonant-excitation mass spectrometry. The dynamics of the reactive processes including the radiative formation of CaRb+ and BaRb+ molecular ions has been analyzed using accurate potential energy curves and quantum-scattering calculations for the radiative channels. It is shown that the energy dependence of the reaction rates is governed by long-range interactions, while its magnitude is determined by short-range non-adiabatic and radiative couplings. The quantum character of the collisions is predicted to manifest itself in the occurrence of narrow shape resonances at well-defined collision energies. The present results highlight both universal and system-specific phenomena in cold ion-neutral collisions. This work was supported by the Swiss National Science Foundation and the COST Action ''Ion Traps for Tomorrow's Applications''.

EPR investigation of electronic excitations in rare gas solids (Review Article)

NASA Astrophysics Data System (ADS)

Zhitnikov, R. A.; Dmitriev, Yu. A.

1998-10-01

The methods are described for producing unstable paramagnetic excited states in rare gas cryocrystals Ne, Ar, Kr, and Xe through the trapping, in the cryocrystals growing from the gas phase, the products of the gas discharge taking place in the same or other rare gas. The paper presents a technique and results of an observation and investigation of excited states in rare gas cryocrystals with electron paramagnetic resonance (EPR). The discovered unstable paramagnetic centers are interpreted as being local metastable excited np5(n+1)s atomic-type states in rare gas cryocrystals which are subject to the action of the anisotropic electric field resulted from the crystal surroundings distorted by the center. An account is given of the mechanisms for formation of observed paramagnetic excited states in cryocrystals which arise owing to the excitation energy of the metastable 3P2 atoms of Ne, Ar, Kr, Xe and He 23S1 and 21S0 atoms that form in the discharge in an appropriate gas and trap in the growing cryocrystal.

Parametric excitation and squeezing in a many-body spinor condensate

PubMed Central

Hoang, T. M.; Anquez, M.; Robbins, B. A.; Yang, X. Y.; Land, B. J.; Hamley, C. D.; Chapman, M. S.

2016-01-01

Atomic spins are usually manipulated using radio frequency or microwave fields to excite Rabi oscillations between different spin states. These are single-particle quantum control techniques that perform ideally with individual particles or non-interacting ensembles. In many-body systems, inter-particle interactions are unavoidable; however, interactions can be used to realize new control schemes unique to interacting systems. Here we demonstrate a many-body control scheme to coherently excite and control the quantum spin states of an atomic Bose gas that realizes parametric excitation of many-body collective spin states by time varying the relative strength of the Zeeman and spin-dependent collisional interaction energies at multiples of the natural frequency of the system. Although parametric excitation of a classical system is ineffective from the ground state, we show that in our experiment, parametric excitation from the quantum ground state leads to the generation of quantum squeezed states. PMID:27044675

Parametric excitation and squeezing in a many-body spinor condensate

NASA Astrophysics Data System (ADS)

Hoang, T. M.; Anquez, M.; Robbins, B. A.; Yang, X. Y.; Land, B. J.; Hamley, C. D.; Chapman, M. S.

2016-04-01

Atomic spins are usually manipulated using radio frequency or microwave fields to excite Rabi oscillations between different spin states. These are single-particle quantum control techniques that perform ideally with individual particles or non-interacting ensembles. In many-body systems, inter-particle interactions are unavoidable; however, interactions can be used to realize new control schemes unique to interacting systems. Here we demonstrate a many-body control scheme to coherently excite and control the quantum spin states of an atomic Bose gas that realizes parametric excitation of many-body collective spin states by time varying the relative strength of the Zeeman and spin-dependent collisional interaction energies at multiples of the natural frequency of the system. Although parametric excitation of a classical system is ineffective from the ground state, we show that in our experiment, parametric excitation from the quantum ground state leads to the generation of quantum squeezed states.

Electron-Excited X-Ray Microanalysis at Low Beam Energy: Almost Always an Adventure!

PubMed

Newbury, Dale E; Ritchie, Nicholas W M

2016-08-01

Scanning electron microscopy with energy-dispersive spectrometry has been applied to the analysis of various materials at low-incident beam energies, E 0≤5 keV, using peak fitting and following the measured standards/matrix corrections protocol embedded in the National Institute of Standards and Technology Desktop Spectrum Analyzer-II analytical software engine. Low beam energy analysis provides improved spatial resolution laterally and in-depth. The lower beam energy restricts the atomic shells that can be ionized, reducing the number of X-ray peak families available to the analyst. At E 0=5 keV, all elements of the periodic table except H and He can be measured. As the beam energy is reduced below 5 keV, elements become inaccessible due to lack of excitation of useful characteristic X-ray peaks. The shallow sampling depth of low beam energy microanalysis makes the technique more sensitive to surface compositional modification due to formation of oxides and other reaction layers. Accurate and precise analysis is possible with the use of appropriate standards and by accumulating high count spectra of unknowns and standards (>1 million counts integrated from 0.1 keV to E 0).

Characterizing Plasmonic Excitations of Quasi-2D Chains

NASA Astrophysics Data System (ADS)

Townsend, Emily; Bryant, Garnett

A quantum description of the optical response of nanostructures and other atomic-scale systems is desirable for modeling systems that use plasmons for quantum information transfer, or coherent transport and interference of quantum states, as well as systems small enough for electron tunneling or quantum confinement to affect the electronic states of the system. Such a quantum description is complicated by the fact that collective and single-particle excitations can have similar energies and thus will mix. We seek to better understand the excitations of nanosystems to identify which characteristics of the excitations are most relevant to modeling their behavior. In this work we use a quasi 2-dimensional linear atomic chain as a model system, and exact diagonalization of the many-body Hamiltonian to obtain its excitations. We compare this to previous work in 1-d chains which used a combination of criteria involving a many-body state's transfer dipole moment, balance, transfer charge, dynamical response, and induced-charge distribution to identify which excitations are plasmonic in character.

Collisional quenching dynamics and reactivity of highly vibrationally excited molecules

NASA Astrophysics Data System (ADS)

Liu, Qingnan

Highly excited molecules are of great importance in many areas of chemistry including photochemistry. The dynamics of highly excited molecules are affected by the intermolecular and intramolecular energy flow between many different kinds of motions. This thesis reports investigations of the collisional quenching and reactivity of highly excited molecules aimed at understanding the dynamics of highly excited molecules. There are several important questions that are addressed. How do molecules behave in collisions with a bath gas? How do the energy distributions evolve in time? How is the energy partitioned for both the donor and bath molecules after collisions? How do molecule structure, molecule state density and intermolecular potential play the role during collisional energy transfer? To answer these questions, collisional quenching dynamics and reactivity of highly vibrationally excited azabenzene molecules have been studied using high resolution transient IR absorption spectroscopy. The first study shows that the alkylated pyridine molecules that have been excited with Evib˜38,800 cm-1 impart less rotational and translational energy to CO2 than pyridine does. Comparison between the alkylated donors shows that the strong collisions are reduced for donors with longer alkyl chains by lowering the average energy per mode but longer alkyl chain have increased flexibility and higher state densities that enhance energy loss via strong collisions. In the second study, the role of hydrogen bonding interactions is explored in collision of vibrationally excited pyridines with H2O. Substantial difference in the rotational energy of H 2O is correlated with the structure of the global energy minimum. A torque-inducing mechanism is proposed that involves directed movement of H 2O between sigma and pi-hydrogen bonding interactions with the pyridine donors. In the third study the dynamics of strong and weak collisions for highly vibrationally excited methylated pyridine

Accurate Cross Sections for Excitation of Resonance Transitions in Atomic Oxygen

NASA Technical Reports Server (NTRS)

Tayal, S. S.

2004-01-01

Electron collision excitation cross sections for the resonance 2p(sup)4 (sup 3)P-2p(sup 3)3s (sup 3)S(sup 0), 2p(sup 4) (sup 3)P-2p(sup 3)3d (sup 3)D(sup 0), 2p4 (sup 3)P-2p(sup 3)3s (sup 3)D(sup 0), 2p(sup 4) (sup 3)P-2p(sup 3)3s (sup 3)P(sup 0) and 2p(sup 4) (sup 3)P-2s2p(sup 5) (sup 3)P(sup 0) transitions have been calculated by using the R matrix with a pseudostates approach for incident electron energies from near threshold to 100 eV. The excitation of these transition sgives rise to strong atomic oxygen emission features at 1304, 1027, 989, 878, and 792 Angstrom in the spectra of several planetary atmospheres. We included 22 spectroscopic bound and autoionizing states and 30 pseudostates in the close-coupling expansion. The target wave functions are chosen to properly account for the important correlation and relaxation effects. The effect of coupling to the continuum is included through the use of pseudostates. The contribution of the ionization continuum is significant for resonance transitions. Measured absolute direct excitation cross sections of 0 I are reported by experimental groups from the Jet Propulsion Laboratory and Johns Hopkins University. Good agreement is noted for the 2p(sup)4 (sup 3)P-2p(sup 3)3s (sup 3)S(sup 0) transition (lambda 1304 Ang) with measured cross sections from both groups that agree well with each other. There is disagreement between experiments for other transitions. Our results support the measured cross sections from the Johns Hopkins University for the 2p(sup 4) (sup 3)P-2p(sup 3)3d (sup 3)D(sup 0) and 2p4 (sup 3)P-2p(sup 3)3s (sup 3)D(sup 0) transitions, while for the 2p4 (sup 3)P-2p(sup 3)3s (sup 3)D(sup 0) transition the agreement is switched to the measured cross sections from the Jet Propulsion Laboratory.

Optimised effective potential for ground states, excited states, and time-dependent phenomena

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gross, E.K.U.

1996-12-31

(1) The optimized effective potential method is a variant of the traditional Kohn-Sham scheme. In this variant, the exchange-correlation energy E{sub xc} is an explicit functional of single-particle orbitals. The exchange-correlation potential, given as usual by the functional derivative v{sub xc} = {delta}E{sub xc}/{delta}{rho}, then satisfies as integral equation involving the single-particle orbitals. This integral equation in solved semi-analytically using a scheme recently proposed by Krieger, Li and Iafrate. If the exact (Fock) exchange-energy functional is employed together with the Colle-Salvetti orbital functional for the correlation energy, the mean absolute deviation of the resulting ground-state energies from the exact nonrelativisticmore » values is CT mH for the first-row atoms, as compared to 4.5 mH in a state-of-the-art CI calculation. The proposed scheme is thus significantly more accurate than the conventional Kohn-Sham method while the numerical effort involved is about the same as for an ordinary Hanree-Fock calculation. (2) A time-dependent generalization of the optimized-potential method is presented and applied to the linear-response regime. Since time-dependent density functional theory leads to a formally exact representation of the frequency-dependent linear density response and since the latter, as a function of frequency, has poles at the excitation energies of the fully interacting system, the formalism is suitable for the calculation of excitation energies. A simple additive correction to the Kohn-Sham single-particle excitation energies will be deduced and first results for atomic and molecular singlet and triplet excitation energies will be presented. (3) Beyond the regime of linear response, the time-dependent optimized-potential method is employed to describe atoms in strong emtosecond laser pulses. Ionization yields and harmonic spectra will be presented and compared with experimental data.« less

Dynamics of a single-atom electron pump.

PubMed

van der Heijden, J; Tettamanzi, G C; Rogge, S

2017-03-15

Single-electron pumps based on isolated impurity atoms have recently been experimentally demonstrated. In these devices the Coulomb potential of an atom creates a localised electron state with a large charging energy and considerable orbital level spacings, enabling robust charge capturing processes. In contrast to the frequently used gate-defined quantum dot pumps, which experience a strongly time-dependent potential, the confinement potential in these single-atom pumps is hardly affected by the periodic driving of the system. Here we describe the behaviour and performance of an atomic, single parameter, electron pump. This is done by considering the loading, isolating and unloading of one electron at the time, on a phosphorous atom embedded in a silicon double gate transistor. The most important feature of the atom pump is its very isolated ground state, which is populated through the fast loading of much higher lying excited states and a subsequent fast relaxation process. This leads to a substantial increase in pumping accuracy, and is opposed to the adverse role of excited states observed for quantum dot pumps due to non-adiabatic excitations. The pumping performance is investigated as a function of dopant position, revealing a pumping behaviour robust against the expected variability in atomic position.

Dynamics of a single-atom electron pump

PubMed Central

van der Heijden, J.; Tettamanzi, G. C.; Rogge, S.

2017-01-01

Single-electron pumps based on isolated impurity atoms have recently been experimentally demonstrated. In these devices the Coulomb potential of an atom creates a localised electron state with a large charging energy and considerable orbital level spacings, enabling robust charge capturing processes. In contrast to the frequently used gate-defined quantum dot pumps, which experience a strongly time-dependent potential, the confinement potential in these single-atom pumps is hardly affected by the periodic driving of the system. Here we describe the behaviour and performance of an atomic, single parameter, electron pump. This is done by considering the loading, isolating and unloading of one electron at the time, on a phosphorous atom embedded in a silicon double gate transistor. The most important feature of the atom pump is its very isolated ground state, which is populated through the fast loading of much higher lying excited states and a subsequent fast relaxation process. This leads to a substantial increase in pumping accuracy, and is opposed to the adverse role of excited states observed for quantum dot pumps due to non-adiabatic excitations. The pumping performance is investigated as a function of dopant position, revealing a pumping behaviour robust against the expected variability in atomic position. PMID:28295055

Rotational excitation of hydrogen molecules by collisions with hydrogen atoms. [interstellar gas energetics

NASA Technical Reports Server (NTRS)

Green, S.; Truhlar, D. G.

1979-01-01

Rate constants for rotational excitation of hydrogen molecules by collisions with hydrogen atoms have been obtained from quantum-mechanical calculations for kinetic temperatures between 100 and 5000 K. These calculations involve the rigid-rotator approximation, but other possible sources of error should be small. The calculations indicate that the early values of Nishimura are larger than accurate rigid-rotator values by about a factor of 20 or more.

Excitation energy dependent Raman spectrum of MoSe2

PubMed Central

Nam, Dahyun; Lee, Jae-Ung; Cheong, Hyeonsik

2015-01-01

Raman investigation of MoSe2 was carried out with eight different excitation energies. Seven peaks, including E1g, A1g, E2g1, and A2u2 peaks are observed in the range of 100–400 cm−1. The phonon modes are assigned by comparing the peak positions with theoretical calculations. The intensities of the peaks are enhanced at different excitation energies through resonance with different optical transitions. The A1g mode is enhanced at 1.58 and 3.82 eV, which are near the A exciton energy and the band-to-band transition between higher energy bands, respectively. The E2g1 mode is strongly enhanced with respect to the A1g mode for the 2.71- and 2.81-eV excitations, which are close to the C exciton energy. The different enhancements of the A1g and E2g1 modes are explained in terms of the symmetries of the exciton states and the exciton-phonon coupling. Other smaller peaks including E1g and A2u2 are forbidden but appear due to the resonance effect near optical transition energies. PMID:26601614

Excitation energy transfer in the photosystem I

DOE Office of Scientific and Technical Information (OSTI.GOV)

Webber, Andrew N

2012-09-25

Photosystem I is a multimeric pigment protein complex in plants, green alage and cyanobacteria that functions in series with Photosystem II to use light energy to oxidize water and reduce carbon dioxide. The Photosystem I core complex contains 96 chlorophyll a molecules and 22 carotenoids that are involved in light harvesting and electron transfer. In eucaryotes, PSI also has a peripheral light harvesting complex I (LHCI). The role of specific chlorophylls in excitation and electron transfer are still unresolved. In particular, the role of so-called bridging chlorophylls, located between the bulk antenna and the core electron transfer chain, in themore » transfer of excitation energy to the reaction center are unknown. During the past funding period, site directed mutagenesis has been used to create mutants that effect the physical properties of these key chlorophylls, and to explore how this alters the function of the photosystem. Studying these mutants using ultrafast absorption spectroscopy has led to a better understanding of the process by which excitation energy is transferred from the antenna chlorophylls to the electron transfer chain chlorophylls, and what the role of connecting chlorophylls and A_0 chlorophylls is in this process. We have also used these mutants to investigate whch of the central group of six chlorophylls are involved in the primary steps of charge separation and electron transfer.« less

Geometry dependent suppression of collective quantum jumps in Rydberg atoms

NASA Astrophysics Data System (ADS)

Lees, Eitan; Clemens, James

2015-05-01

We consider N driven, damped Rydberg atoms in different spatial arrangements. Treating the atoms as two-level systems we model the coupling to the environment via the Lehmberg-Agarwal master equation which interpolates between fully independent and fully collective spontaneous emission depending on the specific locations of the atoms. We also include a collective dipole-dipole energy shift in the excited Rydberg state which leads to collective quantum jumps in the atomic excitation when the system is driven off resonance. We show that the quantum jumps are suppressed as the system makes a transition from independent to collective emission as the spacing of a linear array of atoms is decreased below the emission wavelength.

Excited electronic states of the methyl radical. Ab initio molecular orbital study of geometries, excitation energies and vibronic spectra

NASA Astrophysics Data System (ADS)

Mebel, Alexander M.; Lin, Sheng-Hsien

1997-03-01

The geometries, vibrational frequencies and vertical and adiabatic excitation energies of the excited valence and Rydberg 3s, 3p, 3d, and 4s electronic states of CH 3 have been studied using ab initio molecular orbital multiconfigurational SCF (CASSCF), internally contracted multireference configuration interaction (MRCI) and equation-of-motion coupled cluster (EOM-CCSD) methods. The vibronic spectra are determined through the calculation of Franck-Condon factors. Close agreement between theory and experiment has been found for the excitation energies, vibrational frequencies and vibronic spectra. The adiabatic excitation energies of the Rydberg 3s B˜ 2A' 1 and 3p 2 2A″ 2 states are calculated to be 46435 and 60065 cm -1 compared to the experimental values of 46300 and 59972 cm -1, respectively. The valence 2A″ excited state of CH 3 has been found to have a pyramidal geometry within C s symmetry and to be adiabatically by 97 kcal/mol higher in energy than the ground state. The 2A″ state is predicted to be stable by 9 and 13 kcal/mol with respect to H 2 and H elimination.

Attosecond XUV absorption spectroscopy of doubly excited states in helium atoms dressed by a time-delayed femtosecond infrared laser

NASA Astrophysics Data System (ADS)

Yang, Z. Q.; Ye, D. F.; Ding, Thomas; Pfeifer, Thomas; Fu, L. B.

2015-01-01

In the present paper, we investigate the time-resolved transient absorption spectroscopy of doubly excited states of helium atoms by solving the time-dependent two-electron Schrödinger equation numerically based on a one-dimensional model. The helium atoms are subjected to an extreme ultraviolet (XUV) attosecond pulse and a time-delayed infrared (IR) few-cycle laser pulse. A superposition of doubly excited states populated by the XUV pulse is identified, which interferes with the direct ionization pathway leading to Fano resonance profiles in the photoabsorption spectrum. In the presence of an IR laser, however, the Fano line profiles are strongly modified: A shifting, splitting, and broadening of the original absorption lines is observed when the XUV attosecond pulse and infrared few-cycle laser pulse overlap in time, which is in good agreement with recent experimental results. At certain time delays, we observe symmetric Lorentz, inverted Fano profiles, and even negative absorption cross sections indicating that the XUV light can be amplified during the interaction with atoms. We further prove that the above pictures are general for different doubly excited states by suitably varying the frequency of the IR field to coherently couple the corresponding states.

Emission line shapes produced by dissociative excitation of atmospheric gases

NASA Technical Reports Server (NTRS)

Zipf, E. C.; Wells, W. C.

1980-01-01

The spectral line shapes of the radiation emitted from O atoms produced by the dissociative excitation of O2, CO, CO2 and NO are investigated. Doppler line shapes are derived from time-of-flight spectra of O (5S0) atoms decaying by the emission of 1356-A radiation after being produced in electron impact experiments at incident electron energies from 25 to 300 eV. It is shown that the effective line width of the radiation is large compared with the Doppler absorption widths of ambient O atoms in both photoelectron and auroral excitation, and thus the dissociatively excited component of the O I 1304-A airglow will behave as though it were optically thin, exhibiting pronounced limb brightening effects and a scale height characteristic of the initial, local source function. It is found that the average kinetic energy of the dissociation fragments inferred from O I (5S) time-of-flight spectra is in good agreement with that of O I (3S) atoms in the electron impact dissociation of CO2, although not for O2. Finally, it is suggested that although electron impact dissociation of CO and CO2 contributes to the 1304-A emission in the upper atmosphere of Venus, it cannot be the dominant source of this radiation since the absolute cross sections for the reaction are too small.

Heavy atom vibrational modes and low-energy vibrational autodetachment in nitromethane anions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Thompson, Michael C.; Weber, J. Mathias, E-mail: weberjm@jila.colorado.edu; Department of Chemistry and Biochemistry, University of Colorado at Boulder, 215UCB, Boulder, Colorado 80309-0215

2015-06-21

We report infrared spectra of nitromethane anion, CH{sub 3}NO{sub 2}{sup −}, in the region 700–2150 cm{sup −1}, obtained by Ar predissociation spectroscopy and electron detachment spectroscopy. The data are interpreted in the framework of second-order vibrational perturbation theory based on coupled-cluster electronic structure calculations. The modes in the spectroscopic region studied here are mainly based on vibrations involving the heavier atoms; this work complements earlier studies on nitromethane anion that focused on the CH stretching region of the spectrum. Electron detachment begins at photon energies far below the adiabatic electron affinity due to thermal population of excited vibrational states.

Reevaluating the mechanism of excitation energy regulation in iron-starved cyanobacteria.

PubMed

Chen, Hui-Yuan S; Liberton, Michelle; Pakrasi, Himadri B; Niedzwiedzki, Dariusz M

2017-03-01

This paper presents spectroscopic investigations of IsiA, a chlorophyll a-binding membrane protein produced by cyanobacteria grown in iron-deficient environments. IsiA, if associated with photosystem I, supports photosystem I in light harvesting by efficiently transferring excitation energy. However, if separated from photosystem I, IsiA exhibits considerable excitation quenching observed as a substantial reduction of protein-bound chlorophyll a fluorescence lifetime. Previous spectroscopic studies suggested that carotenoids are involved in excitation energy dissipation and in addition play a second role in this antenna complex by supporting chlorophyll a in light harvesting by absorbing in the spectral range inaccessible for chlorophyll a and transferring excitation to chlorophylls. However, this investigation does not support these proposed roles of carotenoids in this light harvesting protein. This study shows that carotenoids do not transfer excitation energy to chlorophyll a. In addition, our investigations do not support the hypothesis that carotenoids are quenchers of the excited state of chlorophyll a in this protein complex. We propose that quenching of chlorophyll a fluorescence in IsiA is maintained by pigment-protein interaction via electron transfer from an excited chlorophyll a to a cysteine residue, an excitation quenching mechanism that was recently proposed to regulate the light harvesting capabilities of the bacteriochlorophyll a-containing Fenna-Mathews-Olson protein from green sulfur bacteria. Copyright © 2017 Elsevier B.V. All rights reserved.

Electron-lattice energy relaxation in laser-excited thin-film Au-insulator heterostructures studied by ultrafast MeV electron diffraction

PubMed Central

Sokolowski-Tinten, K.; Shen, X.; Zheng, Q.; Chase, T.; Coffee, R.; Jerman, M.; Li, R. K.; Ligges, M.; Makasyuk, I.; Mo, M.; Reid, A. H.; Rethfeld, B.; Vecchione, T.; Weathersby, S. P.; Dürr, H. A.; Wang, X. J.

2017-01-01

We apply time-resolved MeV electron diffraction to study the electron-lattice energy relaxation in thin film Au-insulator heterostructures. Through precise measurements of the transient Debye-Waller-factor, the mean-square atomic displacement is directly determined, which allows to quantitatively follow the temporal evolution of the lattice temperature after short pulse laser excitation. Data obtained over an extended range of laser fluences reveal an increased relaxation rate when the film thickness is reduced or the Au-film is capped with an additional insulator top-layer. This behavior is attributed to a cross-interfacial coupling of excited electrons in the Au film to phonons in the adjacent insulator layer(s). Analysis of the data using the two-temperature-model taking explicitly into account the additional energy loss at the interface(s) allows to deduce the relative strength of the two relaxation channels. PMID:28795080

Electronic excitations in finite and infinite polyenes

NASA Astrophysics Data System (ADS)

Tavan, Paul; Schulten, Klaus

1987-09-01

We study electronic excitations in long polyenes, i.e., in one-dimensional strongly correlated electron systems which are neither infinite nor small. The excitations are described within Hubbard and Pariser-Parr-Pople (PPP) models by means of a multiple-reference double-excitation expansion [P. Tavan and K. Schulten, J. Chem. Phys. 85, 6602 (1986)]. We find that quantized ``transition'' momenta can be assigned to electronic excitations in finite chains. These momenta link excitation energies of finite chains to dispersion relations of infinite chains, i.e., they bridge the gap between finite and infinite systems. A key result is the following: Excitation energies E in polyenes with N carbon atoms are described very accurately by the formula Eβ=ΔEβ0+αβk(N)q, q=1,2,..., where β denotes the excitation class, ΔEβ0 the energy gap in the infinite system [αβk(N)>0], and k(N) the elementary transition momentum. The parameters ΔEβ0 and αβ are determined for covalent and ionic excitations in alternating and nonalternating polyenes. The covalent excitations are combinations of triplet excitations T, i.e., T, TT, TTT, . . . . The lowest singlet excitations in the infinite polyene, e.g., in polyacetylene or polydiacetylene, are TT states. Available evidence proves that these states can dissociate into separate triplets. The bond structure of TT states is that of a neutral soliton-antisoliton pair. The level density of TT states in long polyenes is high enough to allow dissociation into separate solitons.

Energetic Metastable Oxygen and Nitrogen Atoms in the Terrestrial Atmosphere

NASA Technical Reports Server (NTRS)

Kharchenko, Vasili; Dalgarno, A.

2005-01-01

This report summarizes our research performed under NASA Grant NAG5-11857. The three-year grant have been supported by the Geospace Sciences SR&T program. We have investigated the energetic metastable oxygen and nitrogen atoms in the terrestrial stratosphere, mesosphere and thermosphere. Hot atoms in the atmosphere are produced by solar radiation, the solar wind and various ionic reactions. Nascent hot atoms arise in ground and excited electronic states, and their translational energies are larger by two - three orders of magnitude than the thermal energies of the ambient gas. The relaxation kinetics of hot atoms determines the rate of atmospheric heating, the intensities of aeronomic reactions, and the rate of atom escape from the planet. Modeling of the non-Maxwellian energy distributions of metastable oxygen and nitrogen atoms have been focused on the determination of their impact on the energetics and chemistry of the terrestrial atmosphere between 25 and 250 km . At this altitudes, we have calculated the energy distribution functions of metastable O and N atoms and computed non-equilibrium rates of important aeronomic reactions, such as destruction of the water molecules by O(1D) atoms and production of highly excited nitric oxide molecules. In the upper atmosphere, the metastable O(lD) and N(2D) play important role in formation of the upward atomic fluxes. We have computed the upward fluxes of the metastable and ground state oxygen atoms in the upper atmosphere above 250 km. The accurate distributions of the metastable atoms have been evaluated for the day and night-time conditions.

JANUS - A setup for low-energy Coulomb excitation at ReA3

NASA Astrophysics Data System (ADS)

Lunderberg, E.; Belarge, J.; Bender, P. C.; Bucher, B.; Cline, D.; Elman, B.; Gade, A.; Liddick, S. N.; Longfellow, B.; Prokop, C.; Weisshaar, D.; Wu, C. Y.

2018-03-01

A new experimental setup for low-energy Coulomb excitation experiments was constructed in a collaboration between the National Superconducting Cyclotron Laboratory (NSCL), Lawrence Livermore National Laboratory (LLNL), and the University of Rochester and was commissioned at the general purpose beam line of NSCL's ReA3 reaccelerator facility. The so-called JANUS setup combines γ-ray detection with the Segmented Ge Array (SeGA) and scattered particle detection using a pair of segmented double-sided Si detectors (Bambino 2). The low-energy Coulomb excitation program that JANUS enables will complement intermediate-energy Coulomb excitation studies that have long been performed at NSCL by providing access to observables that quantify collectivity beyond the first excited state, including the sign and magnitude of excited-state quadrupole moments. In this work, the setup and its performance will be described based on the commissioning run that used stable 78Kr impinging onto a 1.09 mg/cm2208Pb target at a beam energy of 3.9 MeV/u.

Atomic data on inelastic processes in low-energy manganese-hydrogen collisions

NASA Astrophysics Data System (ADS)

Belyaev, Andrey K.; Voronov, Yaroslav V.

2017-10-01

Aims: The aim of this paper is to calculate cross sections and rate coefficients for inelastic processes in low-energy Mn + H and Mn+ + H- collisions, especially, for processes with high and moderate rate coefficients. These processes are required for non-local thermodynamic equilibrium (non-LTE) modeling of manganese spectra in cool stellar atmospheres, and in particular, for metal-poor stars. Methods: The calculations of the cross sections and the rate coefficients were performed by means of the quantum model approach within the framework of the Born-Oppenheimer formalism, that is, the asymptotic semi-empirical method for the electronic MnH molecular structure calculation followed by the nonadiabatic nuclear dynamical calculation by means of the multichannel analytic formulas. Results: The cross sections and the rate coefficients for low-energy inelastic processes in manganese-hydrogen collisions are calculated for all transitions between 21 low-lying covalent states and one ionic state. We show that the highest values of the cross sections and the rate coefficients correspond to the mutual neutralization processes into the final atomic states Mn(3d54s(7S)5s e 6S), Mn(3d54s(7S)5p y 8P°), Mn(3d54s(7S)5s e 8S), Mn(3d54s(7S)4d e 8D) [the first group], the processes with the rate coefficients (at temperature T = 6000 K) of the values 4.38 × 10-8, 2.72 × 10-8, 1.98 × 10-8, and 1.59 × 10-8 cm3/ s, respectively, that is, with the rate coefficients exceeding 10-8 cm3/ s. The processes with moderate rate coefficients, that is, with values between 10-10 and 10-8 cm3/ s include many excitation, de-excitation, mutual neutralization and ion-pair formation processes. In addition to other processes involving the atomic states from the first group, the processes from the second group include those involving the following atomic states: Mn(3d5(6S)4s4p (1P°) y 6P°), Mn(3d54s(7S)4d e 6D), Mn(3d54s(7S)5p w 6P°), Mn(3d5(4P)4s4p (3P°) y 6D°), Mn(3d5(4G)4s4p (3P°) y 6F�

Electron impact excitation of the n = 2 to n = 3 transition in atomic hydrogen near threshold

NASA Astrophysics Data System (ADS)

Hata, J.; Morgan, L. A.; McDowell, M. R. C.

1980-06-01

Close-coupling calculations of electron impact excitation of the n = 2 to n = 3 transition of atomic hydrogen at energies below the n = 4 threshold are presented. The algebraic variational close-coupling code of Morgan (1980) with an eighteen-state basis was used to obtain cross sections at eight impact energies from 2.04 to 2.45 eV, and calculations in a six-state close-coupling model were compared with the six-state calculations of Burke et al. (1967). The six-state values are found to be in satisfactory agreement with the exception of the singlet contribution to the 2s-3s transition. Near the n = 3 threshold the cross section obtained in the full calculation is found to be almost a factor of 2 lower than that predicted by Johnson (1972), thus explaining in part the discrepancy between Johnson's results and experiments on hydrogen plasmas. Estimates of rate coefficients based on the cross sections and assuming a Maxwellian velocity distribution, however, are shown to remain in disagreement with experiment.

The Atomization Energy of Mg4

NASA Technical Reports Server (NTRS)

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

1999-01-01

The atomization energy of Mg4 is determined using the MP2 and CCSD(T) levels of theory. Basis set incompleteness, basis set extrapolation, and core-valence effects are discussed. Our best atomization energy, including the zero-point energy and scalar relativistic effects, is 24.6+/-1.6 kcal per mol. Our computed and extrapolated values are compared with previous results, where it is observed that our extrapolated MP2 value is good agreement with the MP2-R12 value. The CCSD(T) and MP2 core effects are found to have the opposite signs.

Correlated natural transition orbital framework for low-scaling excitation energy calculations (CorNFLEx).

PubMed

Baudin, Pablo; Kristensen, Kasper

2017-06-07

We present a new framework for calculating coupled cluster (CC) excitation energies at a reduced computational cost. It relies on correlated natural transition orbitals (NTOs), denoted CIS(D')-NTOs, which are obtained by diagonalizing generalized hole and particle density matrices determined from configuration interaction singles (CIS) information and additional terms that represent correlation effects. A transition-specific reduced orbital space is determined based on the eigenvalues of the CIS(D')-NTOs, and a standard CC excitation energy calculation is then performed in that reduced orbital space. The new method is denoted CorNFLEx (Correlated Natural transition orbital Framework for Low-scaling Excitation energy calculations). We calculate second-order approximate CC singles and doubles (CC2) excitation energies for a test set of organic molecules and demonstrate that CorNFLEx yields excitation energies of CC2 quality at a significantly reduced computational cost, even for relatively small systems and delocalized electronic transitions. In order to illustrate the potential of the method for large molecules, we also apply CorNFLEx to calculate CC2 excitation energies for a series of solvated formamide clusters (up to 4836 basis functions).

Nonmonotonic radial distribution of excited atoms in a positive column of pulsed direct currect discharges in helium

DOE Office of Scientific and Technical Information (OSTI.GOV)

Barnat, E. V.; Kolobov, V. I.

2013-01-21

Nonmonotonic radial distributions of excited helium atoms have been experimentally observed in a positive column of pulsed helium discharges using planar laser induced fluorescence. Computational analysis of the discharge dynamics with a fluid plasma model confirms the experimental observations over a range of pressures and currents. The observed effect is attributed to the peculiarities of electron population-depopulation of the excited states during the 'dynamic discharge' conditions with strong modulations of the electric field maintaining the plasma.

The Atomic Energy Commission's Annual Report to Congress for 1960. Major Activities in the Atomic Energy Programs, January - December 1960

DOE Office of Scientific and Technical Information (OSTI.GOV)

McCone, John A.

1961-01-31

The document covers activities for the period January - December 1960. The report consists of two parts: Part One, The Atomic Energy Industry in 1960 and Related Activities; and Part Two, Major Activities in Atomic Energy Programs. Twenty-one appendices are also included.

FAC: Flexible Atomic Code

NASA Astrophysics Data System (ADS)

Gu, Ming Feng

2018-02-01

FAC calculates various atomic radiative and collisional processes, including radiative transition rates, collisional excitation and ionization by electron impact, energy levels, photoionization, and autoionization, and their inverse processes radiative recombination and dielectronic capture. The package also includes a collisional radiative model to construct synthetic spectra for plasmas under different physical conditions.

Excitation energy dependence of excited states dynamics in all- trans-carotenes determined by femtosecond absorption and fluorescence spectroscopy

NASA Astrophysics Data System (ADS)

Kosumi, Daisuke; Yanagi, Kazuhiro; Nishio, Tomohiro; Hashimoto, Hideki; Yoshizawa, Masayuki

2005-06-01

Ultrafast relaxation kinetics in β-carotene and lycopene has been investigated by femtosecond absorption and fluorescence spectroscopies using tunable excitation pulses. The transient signals induced by the photoexcitation with larger excess energy have broader bands and longer lifetimes both in the 11Bu+and21Ag- excited states. The excess vibrational energy remains longer than several picoseconds and slows the relaxation kinetics in carotenoids.

Spectroscopic properties of the S1 state of linear carotenoids after excess energy excitation

NASA Astrophysics Data System (ADS)

Kuznetsova, Valentyna; Southall, June; Cogdell, Richard J.; Fuciman, Marcel; Polívka, Tomáš

2017-09-01

Properties of the S1 state of neurosporene, spheroidene and lycopene were studied after excess energy excitation in the S2 state. Excitation of carotenoids into higher vibronic levels of the S2 state generates excess vibrational energy in the S1 state. The vibrationally hot S1 state relaxes faster when carotenoid is excited into the S2 state with excess energy, but the S1 lifetime remains constant regardless of which vibronic level of the S2 state is excited. The S∗ signal depends on excitation energy only for spheroidene, which is likely due to asymmetry of the molecule, facilitating conformations responsible for the S∗ signal.

Interaction-Free Effects Between Distant Atoms

NASA Astrophysics Data System (ADS)

Aharonov, Yakir; Cohen, Eliahu; Elitzur, Avshalom C.; Smolin, Lee

2018-01-01

A Gedanken experiment is presented where an excited and a ground-state atom are positioned such that, within the former's half-life time, they exchange a photon with 50% probability. A measurement of their energy state will therefore indicate in 50% of the cases that no photon was exchanged. Yet other measurements would reveal that, by the mere possibility of exchange, the two atoms have become entangled. Consequently, the "no exchange" result, apparently precluding entanglement, is non-locally established between the atoms by this very entanglement. This quantum-mechanical version of the ancient Liar Paradox can be realized with already existing transmission schemes, with the addition of Bell's theorem applied to the no-exchange cases. Under appropriate probabilities, the initially-excited atom, still excited, can be entangled with additional atoms time and again, or alternatively, exert multipartite nonlocal correlations in an interaction free manner. When densely repeated several times, this result also gives rise to the Quantum Zeno effect, again exerted between distant atoms without photon exchange. We discuss these experiments as variants of interaction-free-measurement, now generalized for both spatial and temporal uncertainties. We next employ weak measurements for elucidating the paradox. Interpretational issues are discussed in the conclusion, and a resolution is offered within the Two-State Vector Formalism and its new Heisenberg framework.

Interaction-Free Effects Between Distant Atoms

NASA Astrophysics Data System (ADS)

Aharonov, Yakir; Cohen, Eliahu; Elitzur, Avshalom C.; Smolin, Lee

2017-12-01

A Gedanken experiment is presented where an excited and a ground-state atom are positioned such that, within the former's half-life time, they exchange a photon with 50% probability. A measurement of their energy state will therefore indicate in 50% of the cases that no photon was exchanged. Yet other measurements would reveal that, by the mere possibility of exchange, the two atoms have become entangled. Consequently, the "no exchange" result, apparently precluding entanglement, is non-locally established between the atoms by this very entanglement. This quantum-mechanical version of the ancient Liar Paradox can be realized with already existing transmission schemes, with the addition of Bell's theorem applied to the no-exchange cases. Under appropriate probabilities, the initially-excited atom, still excited, can be entangled with additional atoms time and again, or alternatively, exert multipartite nonlocal correlations in an interaction free manner. When densely repeated several times, this result also gives rise to the Quantum Zeno effect, again exerted between distant atoms without photon exchange. We discuss these experiments as variants of interaction-free-measurement, now generalized for both spatial and temporal uncertainties. We next employ weak measurements for elucidating the paradox. Interpretational issues are discussed in the conclusion, and a resolution is offered within the Two-State Vector Formalism and its new Heisenberg framework.

Atomic Processes for XUV Lasers: Alkali Atoms and Ions

NASA Astrophysics Data System (ADS)

Dimiduk, David Paul

The development of extreme ultraviolet (XUV) lasers is dependent upon knowledge of processes in highly excited atoms. Described here are spectroscopy experiments which have identified and characterized certain autoionizing energy levels in core-excited alkali atoms and ions. Such levels, termed quasi-metastable, have desirable characteristics as upper levels for efficient, powerful XUV lasers. Quasi -metastable levels are among the most intense emission lines in the XUV spectra of core-excited alkalis. Laser experiments utilizing these levels have proved to be useful in characterizing other core-excited levels. Three experiments to study quasi-metastable levels are reported. The first experiment is vacuum ultraviolet (VUV) absorption spectroscopy on the Cs 109 nm transitions using high-resolution laser techniques. This experiment confirms the identification of transitions to a quasi-metastable level, estimates transition oscillator strengths, and estimates the hyperfine splitting of the quasi-metastable level. The second experiment, XUV emission spectroscopy of Ca II and Sr II in a microwave-heated plasma, identifies transitions from quasi-metastable levels in these ions, and provides confirming evidence of their radiative, rather than autoionizing, character. In the third experiment, core-excited Ca II ions are produced by inner-shell photoionization of Ca with soft x-rays from a laser-produced plasma. This preliminary experiment demonstrated a method of creating large numbers of these highly-excited ions for future spectroscopic experiments. Experimental and theoretical evidence suggests the CA II 3{ rm p}^5 3d4s ^4 {rm F}^circ_{3/2 } quasi-metastable level may be directly pumped via a dipole ionization process from the Ca I ground state. The direct process is permitted by J conservation, and occurs due to configuration mixing in the final state and possibly the initial state as well. The experiments identifying and characterizing quasi-metastable levels are

Energy resolved actinometry for simultaneous measurement of atomic oxygen densities and local mean electron energies in radio-frequency driven plasmas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Greb, Arthur, E-mail: ag941@york.ac.uk; Niemi, Kari; O'Connell, Deborah

2014-12-08

A diagnostic method for the simultaneous determination of atomic oxygen densities and mean electron energies is demonstrated for an atmospheric pressure radio-frequency plasma jet. The proposed method is based on phase resolved optical emission measurements of the direct and dissociative electron-impact excitation dynamics of three distinct emission lines, namely, Ar 750.4 nm, O 777.4 nm, and O 844.6 nm. The energy dependence of these lines serves as basis for analysis by taking into account two line ratios. In this frame, the method is highly adaptable with regard to pressure and gas composition. Results are benchmarked against independent numerical simulations and two-photon absorption laser-inducedmore » fluorescence experiments.« less

Ab initio molecular dynamics calculations on scattering of hyperthermal H atoms from Cu(111) and Au(111).

PubMed

Kroes, Geert-Jan; Pavanello, Michele; Blanco-Rey, María; Alducin, Maite; Auerbach, Daniel J

2014-08-07

Energy loss from the translational motion of an atom or molecule impinging on a metal surface to the surface may determine whether the incident particle can trap on the surface, and whether it has enough energy left to react with another molecule present at the surface. Although this is relevant to heterogeneous catalysis, the relative extent to which energy loss of hot atoms takes place to phonons or electron-hole pair (ehp) excitation, and its dependence on the system's parameters, remain largely unknown. We address these questions for two systems that present an extreme case of the mass ratio of the incident atom to the surface atom, i.e., H + Cu(111) and H + Au(111), by presenting adiabatic ab initio molecular dynamics (AIMD) predictions of the energy loss and angular distributions for an incidence energy of 5 eV. The results are compared to the results of AIMDEFp calculations modeling energy loss to ehp excitation using an electronic friction ("EF") model applied to the AIMD trajectories, so that the energy loss to the electrons is calculated "post" ("p") the computation of the AIMD trajectory. The AIMD calculations predict average energy losses of 0.38 eV for Cu(111) and 0.13-0.14 eV for Au(111) for H-atoms that scatter from these surfaces without penetrating the surface. These energies closely correspond with energy losses predicted with Baule models, which is suggestive of structure scattering. The predicted adiabatic integral energy loss spectra (integrated over all final scattering angles) all display a lowest energy peak at an energy corresponding to approximately 80% of the average adiabatic energy loss for non-penetrative scattering. In the adiabatic limit, this suggests a way of determining the approximate average energy loss of non-penetratively scattered H-atoms from the integral energy loss spectrum of all scattered H-atoms. The AIMDEFp calculations predict that in each case the lowest energy loss peak should show additional energy loss in the

Ab initio molecular dynamics calculations on scattering of hyperthermal H atoms from Cu(111) and Au(111)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kroes, Geert-Jan, E-mail: g.j.kroes@chem.leidenuniv.nl; Pavanello, Michele; Blanco-Rey, María

2014-08-07

Energy loss from the translational motion of an atom or molecule impinging on a metal surface to the surface may determine whether the incident particle can trap on the surface, and whether it has enough energy left to react with another molecule present at the surface. Although this is relevant to heterogeneous catalysis, the relative extent to which energy loss of hot atoms takes place to phonons or electron-hole pair (ehp) excitation, and its dependence on the system's parameters, remain largely unknown. We address these questions for two systems that present an extreme case of the mass ratio of themore » incident atom to the surface atom, i.e., H + Cu(111) and H + Au(111), by presenting adiabatic ab initio molecular dynamics (AIMD) predictions of the energy loss and angular distributions for an incidence energy of 5 eV. The results are compared to the results of AIMDEFp calculations modeling energy loss to ehp excitation using an electronic friction (“EF”) model applied to the AIMD trajectories, so that the energy loss to the electrons is calculated “post” (“p”) the computation of the AIMD trajectory. The AIMD calculations predict average energy losses of 0.38 eV for Cu(111) and 0.13-0.14 eV for Au(111) for H-atoms that scatter from these surfaces without penetrating the surface. These energies closely correspond with energy losses predicted with Baule models, which is suggestive of structure scattering. The predicted adiabatic integral energy loss spectra (integrated over all final scattering angles) all display a lowest energy peak at an energy corresponding to approximately 80% of the average adiabatic energy loss for non-penetrative scattering. In the adiabatic limit, this suggests a way of determining the approximate average energy loss of non-penetratively scattered H-atoms from the integral energy loss spectrum of all scattered H-atoms. The AIMDEFp calculations predict that in each case the lowest energy loss peak should show additional

Accurate calculation of dynamic Stark shifts and depopulation rates of Rydberg energy levels induced by blackbody radiation. Hydrogen, helium, and alkali-metal atoms

DOE Office of Scientific and Technical Information (OSTI.GOV)

Farley, J.W.; Wing, W.H.

1981-05-01

A highly excited (Rydberg) atom bathed in blackbody radiation is perturbed in two ways. A dynamic Stark shift is induced by the off-resonant components of the blackbody radiation. Additionally, electric-dipole transitions to other atomic energy levels are induced by the resonant components of the blackbody radiation. This depopulation effect shortens the Rydberg-state lifetime, thereby broadening the energy level. Calculations of these two effects in many states of hydrogen, helium, and the alkali-metal atoms Li, Na, K, Rb, and Cs are presented for T = 300 K. Contributions from the entire blackbody spectrum and from both discrete and continuous perturbing statesmore » are included. The accuracy is considerably greater than that of previous estimates.« less

Vector correlations study of the reaction N(2D)+H2(X1Σg+)→NH(a1Δ)+H(2S) with different collision energies and reagent vibration excitations

NASA Astrophysics Data System (ADS)

Li, Yong-Qing; Zhang, Yong-Jia; Zhao, Jin-Feng; Zhao, Mei-Yu; Ding, Yong

2015-11-01

Vector correlations of the reaction are studied based on a recent DMBE-SEC PES for the first excited state of NH2 [J. Phys. Chem. A 114 9644 (2010)] by using a quasi-classical trajectory method. The effects of collision energy and the reagent initial vibrational excitation on cross section and product polarization are investigated for v = 0-5 and j = 0 states in a wide collision energy range (10-50 kcal/mol). The integral cross section could be increased by H2 vibration excitation remarkably based on the DMBE-SEC PES. The different phenomena of differential cross sections with different collision energies and reagent vibration excitations are explained. Particularly, the NH molecules are scattered mainly in the backward hemisphere at low vibration quantum number and evolve from backward to forward direction with increasing vibration quantum number, which could be explained by the fact that the vibrational excitation enlarges the H-H distance in the entrance channel, thus enhancing the probability of collision between N atom and H atom. A further study on product polarization demonstrates that the collision energy and vibrational excitation of the reagent remarkably influence the distributions of P(θr), P(ϕr), and P(θr, ϕr). Project supported by the National Natural Science Foundation of China (Grant Nos. 11474141 and 11404080), the Special Fund Based Research New Technology of Methanol conversion and Coal Instead of Oil, the China Postdoctoral Science Foundation (Grant No. 2014M550158) , the Scientific Research Foundation for the Returned Overseas Chinese Scholars, State Education Ministry of China (Grant No. 2014-1685), and the Program for Liaoning Excellent Talents in University, China (Grant Nos. LJQ2015040 and LJQ2014001).

Quantitative Electron-Excited X-Ray Microanalysis of Borides, Carbides, Nitrides, Oxides, and Fluorides with Scanning Electron Microscopy/Silicon Drift Detector Energy-Dispersive Spectrometry (SEM/SDD-EDS) and NIST DTSA-II.

PubMed

Newbury, Dale E; Ritchie, Nicholas W M

2015-10-01

A scanning electron microscope with a silicon drift detector energy-dispersive X-ray spectrometer (SEM/SDD-EDS) was used to analyze materials containing the low atomic number elements B, C, N, O, and F achieving a high degree of accuracy. Nearly all results fell well within an uncertainty envelope of ±5% relative (where relative uncertainty (%)=[(measured-ideal)/ideal]×100%). Quantification was performed with the standards-based "k-ratio" method with matrix corrections calculated based on the Pouchou and Pichoir expression for the ionization depth distribution function, as implemented in the NIST DTSA-II EDS software platform. The analytical strategy that was followed involved collection of high count (>2.5 million counts from 100 eV to the incident beam energy) spectra measured with a conservative input count rate that restricted the deadtime to ~10% to minimize coincidence effects. Standards employed included pure elements and simple compounds. A 10 keV beam was employed to excite the K- and L-shell X-rays of intermediate and high atomic number elements with excitation energies above 3 keV, e.g., the Fe K-family, while a 5 keV beam was used for analyses of elements with excitation energies below 3 keV, e.g., the Mo L-family.

VizieR Online Data Catalog: H2 d3{Pi}u excitation by elec

NASA Astrophysics Data System (ADS)

Liu, X.; Shemansky, D. E.; Yoshii, J.; Johnson, P. V.; Malone, C. P.; Ajello, J. M.

2016-05-01

Electron-impact excitation of H2 triplet states plays an imp role in the heating of outer planet upper thermospheres. The d3{Pi}u state is the third ungerade triplet state, and the d3{Pi}u-a3{Sigma}g+ emission is the largest cascade channel for the a3{Sigma}g+ state. Accurate energies of the d3{Pi}u-(v, J) levels are calculated from an ab initio potential energy curve. Radiative lifetimes of the d3{Pi}u(v,J) levels are obtained by an accurate evaluation of the d3{Pi}u-a3{Sigma}g+ transition probabilities. The emission yields are determined from experimental lifetimes and calculated radiative lifetimes and are further verified by comparing experimental and synthetic d3{Pi}u-a3{Sigma}g+ spectra at 20eV impact energy. Spectral analysis revealed that multipolar components beyond the dipolar term are required to model the X1{Sigma}g+-d3{Pi}u excitation, and significant cascade excitation occurs at the d3{Pi}u (v=0,1) levels. Kinetic energy (Ek) distributions of H atoms produced via predissociation of the 3{Pi}u state and the d3{Pi}u-a3{Sigma}g+-b3{Sigma}u+ cascade dissociative emission are obtained. Predissociation of the d3{Pi}u state produces H atoms with an average Ek of 2.3+/-0.4 eV/atom, while the Ekdistribution of the d3{Pi}u-a3{Sigma}g+-b3{Sigma}u+ channel is similar to that of the X1{Sigma}g+-a3{Sigma}g+-b3{Sigma}u+ channel and produces H(1s) atoms with an average Ek of 1.15+/-0.05eV/atom. On average, each H2 excited to the d3{Pi}u state in an H2-dominated atmosphere deposits 3.3+/-0.4eV into the atmosphere, while each H2directly excited to the a3{Sigma}g+ state gives 2.2-2.3eV to the atmosphere. The spectral distribution of the calculated a3{Sigma}g+-b3{Sigma}u+ continuum emission due to the X1{Sigma}g+-d3{Pi}u excitation is significantly different from that of direct a3{Sigma}g+ excitation. (2 data files).

Atomic Mass and Nuclear Binding Energy for I-131 (Iodine)

NASA Astrophysics Data System (ADS)

Sukhoruchkin, S. I.; Soroko, Z. N.

This document is part of the Supplement containing the complete sets of data of Subvolume A `Nuclei with Z = 1 - 54' of Volume 22 `Nuclear Binding Energies and Atomic Masses' of Landolt-Börnstein - Group I `Elementary Particles, Nuclei and Atoms'. It provides atomic mass, mass excess, nuclear binding energy, nucleon separation energies, Q-values, and nucleon residual interaction parameters for atomic nuclei of the isotope I-131 (Iodine, atomic number Z = 53, mass number A = 131).

Atomic Mass and Nuclear Binding Energy for F-22 (Fluorine)

NASA Astrophysics Data System (ADS)

Sukhoruchkin, S. I.; Soroko, Z. N.

This document is part of the Supplement containing the complete sets of data of Subvolume A `Nuclei with Z = 1 - 54' of Volume 22 `Nuclear Binding Energies and Atomic Masses' of Landolt-Börnstein - Group I `Elementary Particles, Nuclei and Atoms'. It provides atomic mass, mass excess, nuclear binding energy, nucleon separation energies, Q-values, and nucleon residual interaction parameters for atomic nuclei of the isotope F-22 (Fluorine, atomic number Z = 9, mass number A = 22).

Dissociative excitation of H2, HD, and D2 by electron impact

NASA Technical Reports Server (NTRS)

Carnahan, B. L.; Zipf, E. C.

1977-01-01

Time-of-flight techniques have been used to investigate the electron-impact dissociation of H2, HD, and D2 in order to determine the effect of isotopic mass variation in the target molecule on the dissociative excitation process. At incident electron energies near 100 eV, the time-of-flight spectrum produced from each molecule consists of atoms in the metastable 2s state and in high-lying long-lived Rydberg levels. The individual time-of-flight distributions, kinetic-energy spectra, and relative differential cross sections for these two species resulting from each molecule have been measured. The kinetic-energy spectrum of the Rydberg atoms produced from dissociative excitation of H2 was notably dissimilar in shape from the corresponding distributions produced from HD and D2. Also the 2s and Rydberg production cross sections differed between the three molecules. In the dissociation of the heteronuclear HD molecule, the ratio of fast H(2s) atoms to D(2s) atoms was about 1 to 1, while the same ratio comparing the Rydberg atoms was nearly 2 to 1. These differences indicate the influence of the mass variation on the position of the Franck-Condon region in the production of 2s atoms and on the competition between autoionization and dissociation in the formation of Rydberg fragments.

Determination of the fraction of excited iodine atoms produced by dissociation of iodides in a self-sustained pulsed discharge

NASA Astrophysics Data System (ADS)

Vagin, N. P.; Kochetov, I. V.; Napartovich, A. P.; Yuryshev, N. N.

2017-12-01

Based on the measured absorption coefficient for the atomic iodine transition in the mixtures of iodides with helium we have determined the fractions of the excited atomic iodine produced by dissociation of CH3I, CF3I, i-C3F7I, C2F5I and C2H5I molecules in a self-sustained pulsed discharge. In the 1: (3 - 15) mixtures of iodides with helium at the pressure 133 - 400 Pa these fractions amount to 0.29 for CF3I and CH3I, 0.2 for i-C3F7I, and 0.31 for C2F5I and C2H5I. The accuracy of determining the excited iodine fraction is 10%. The numerical modelling is carried out for the mixtures containing CF3I. The calculated values of the excited iodine fraction for the mixture with CF3I agree well with the experimental data.

The energy structure and decay channels of the 4p6-shell excited states in Sr

NASA Astrophysics Data System (ADS)

Kupliauskienė, A.; Kerevičius, G.; Borovik, V.; Shafranyosh, I.; Borovik, A.

2017-11-01

The ejected-electron spectra arising from the decay of the 4p{}5{{nln}}{\\prime }{l}{\\prime }{n}{\\prime\\prime }{l}{\\prime\\prime } autoionizing states in Sr atoms have been studied precisely at the incident-electron energies close to excitation and ionization thresholds of the 4{{{p}}}6 subshell. The excitation behaviors for 58 lines observed between 12 and 21 eV ejected-electron kinetic energy have been investigated. Also, the ab initio calculations of excitation energies, autoionization probabilities and electron-impact excitation cross sections of the states 4p{}5{{nln}}{\\prime }{l}{\\prime }{n}{\\prime\\prime }{l}{\\prime\\prime } (nl = 4d, 5s, 5p; {n}{\\prime }{l}{\\prime } = 4d, 5s, 5p; {n}{\\prime\\prime }{l}{\\prime\\prime } = 5s, 6s, 7s, 8s, 9s, 5p, 6p, 5d, 6d, 7d, 8d, 4f, 5g) have been performed by employing the large-scale configuration-interaction method in the basis of the solutions of Dirac-Fock-Slater equations. The obtained experimental and theoretical data have been used for the accurate identification of the 60 lines in ejected-electron spectra and the 68 lines observed earlier in photoabsorption spectra. The excitation and decay processes for 105 classified states in the 4p55s{}2{nl}, 4p54d{}2{nl} and 4p55s{{nln}}{\\prime }{l}{\\prime } configurations have been considered in detail. In particular, most of the states lying below the ionization threshold of the 4p6 subshell at 26.92 eV possess up to four decay channels with formation of Sr+ in 5s{}1/2, 4d{}3/{2,5/2} and 5p{}1/{2,3/2} states. Two-step autoionization and two-electron Auger transitions with formation of Sr2+ in the 4p6 {}1{{{S}}}0 ground state are the main decay paths for high-lying autoionizing states. The excitation threshold of the 4{{{p}}}6 subshell in Sr has been established at 20.98 ± 0.05 eV.

Studies of Highly Excited Atoms.

DTIC Science & Technology

1986-04-02

R 2 o i86 Chemical Physics Laboratory " i 0. R . Abrahamson i Vice President Physical Fciences Division ri" - c. -:OP...34 - men I IN RO U TI, .. . . . . . . . . . - .... .... o .. . . . o ......... - TI R SOPA T C LLIS OWZ.... ... . 6 ... ... oo ... .... ... .... . - A...by WA =W + 1ns- 0 (3a) and R = 1’np + ’(n-l)p (3b) .* 7_7. ’ P. z Atom 2 ’b y tom1 SA-846 1-30A FIGURE 2 GEOMETRY OF THE COLLISION OF TWO ATOMS Atom I

Effects of excitation frequency on high-order terahertz sideband generation in semiconductors

NASA Astrophysics Data System (ADS)

Xie, Xiao-Tao; Zhu, Bang-Fen; Liu, Ren-Bao

2013-10-01

We theoretically investigate the effects of the excitation frequency on the plateau of high-order terahertz sideband generation (HSG) in semiconductors driven by intense terahertz (THz) fields. We find that the plateau of the sideband spectrum strongly depends on the detuning between the near-infrared laser field and the band gap. We use the quantum trajectory theory (three-step model) to understand the HSG. In the three-step model, an electron-hole pair is first excited by a weak laser, then driven by the strong THz field, and finally recombined to emit a photon with energy gain. When the laser is tuned below the band gap (negative detuning), the electron-hole generation is a virtual process that requires quantum tunneling to occur. When the energy gained by the electron-hole pair from the THz field is less than 3.17 times the ponderomotive energy (Up), the electron and the hole can be driven to the same position and recombined without quantum tunneling, so that the HSG will have large probability amplitude. This leads to a plateau feature of the HSG spectrum with a high-frequency cutoff at about 3.17Up above the band gap. Such a plateau feature is similar to the case of high-order harmonics generation in atoms where electrons have to overcome the binding energy to escape the atomic core. A particularly interesting excitation condition in HSG is that the laser can be tuned above the band gap (positive detuning), corresponding to the unphysical ‘negative’ binding energy in atoms for high-order harmonic generation. Now the electron-hole pair is generated by real excitation, but the recombination process can be real or virtual depending on the energy gained from the THz field, which determines the plateau feature in HSG. Both the numerical calculation and the quantum trajectory analysis reveal that for positive detuning, the HSG plateau cutoff depends on the frequency of the excitation laser. In particular, when the laser is tuned more than 3.17Up above the band

Analytical excited state forces for the time-dependent density-functional tight-binding method.

PubMed

Heringer, D; Niehaus, T A; Wanko, M; Frauenheim, Th

2007-12-01

An analytical formulation for the geometrical derivatives of excitation energies within the time-dependent density-functional tight-binding (TD-DFTB) method is presented. The derivation is based on the auxiliary functional approach proposed in [Furche and Ahlrichs, J Chem Phys 2002, 117, 7433]. To validate the quality of the potential energy surfaces provided by the method, adiabatic excitation energies, excited state geometries, and harmonic vibrational frequencies were calculated for a test set of molecules in excited states of different symmetry and multiplicity. According to the results, the TD-DFTB scheme surpasses the performance of configuration interaction singles and the random phase approximation but has a lower quality than ab initio time-dependent density-functional theory. As a consequence of the special form of the approximations made in TD-DFTB, the scaling exponent of the method can be reduced to three, similar to the ground state. The low scaling prefactor and the satisfactory accuracy of the method makes TD-DFTB especially suitable for molecular dynamics simulations of dozens of atoms as well as for the computation of luminescence spectra of systems containing hundreds of atoms. (c) 2007 Wiley Periodicals, Inc.

Rydberg blockade in three-atom systems

NASA Astrophysics Data System (ADS)

Barredo, Daniel; Ravets, Sylvain; Labuhn, Henning; Beguin, Lucas; Vernier, Aline; Chicireanu, Radu; Nogrette, Florence; Lahaye, Thierry; Browaeys, Antoine

2014-05-01

The control of individual neutral atoms in arrays of optical tweezers is a promising avenue for quantum science and technology. Here we demonstrate unprecedented control over a system of three Rydberg atoms arranged in linear and triangular configurations. The interaction between Rydberg atoms results in the observation of an almost perfect van der Waals blockade. When the single-atom Rabi frequency for excitation to the Rydberg state is comparable to the interaction energy, we directly observe the anisotropy of the interaction between nD-states. Using the independently measured two-body interaction energy shifts we fully reproduce the dynamics of the three-atom system with a model based on a master equation without any adjustable parameter. Combined with our ability to trap single atoms in arbitrary patterns of 2D arrays of up to 100 traps separated by a few microns, these results are very promising for a scalable implementation of quantum simulation of frustrated quantum magnetism with Rydberg atoms.

Ultrafast non-radiative dynamics of atomically thin MoSe 2

DOE PAGES

Lin, Ming -Fu; Kochat, Vidya; Krishnamoorthy, Aravind; ...

2017-10-17

Non-radiative energy dissipation in photoexcited materials and resulting atomic dynamics provide a promising pathway to induce structural phase transitions in two-dimensional materials. However, these dynamics have not been explored in detail thus far because of incomplete understanding of interaction between the electronic and atomic degrees of freedom, and a lack of direct experimental methods to quantify real-time atomic motion and lattice temperature. Here, we explore the ultrafast conversion of photoenergy to lattice vibrations in a model bi-layered semiconductor, molybdenum diselenide, MoSe 2. Specifically, we characterize sub-picosecond lattice dynamics initiated by the optical excitation of electronic charge carriers in the highmore » electron-hole plasma density regime. Our results focuses on the first ten picosecond dynamics subsequent to photoexcitation before the onset of heat transfer to the substrate, which occurs on a ~100 picosecond time scale. Photoinduced atomic motion is probed by measuring the time dependent Bragg diffraction of a delayed mega-electronvolt femtosecond electron beam. Transient lattice temperatures are characterized through measurement of Bragg peak intensities and calculation of the Debye-Waller factor (DWF). These measurements show a sub-picosecond decay of Bragg diffraction and a correspondingly rapid rise in lattice temperatures. We estimate a high quantum yield for the conversion of excited charge carrier energy to lattice motion under our experimental conditions, indicative of a strong electron-phonon interaction. First principles nonadiabatic quantum molecular dynamics simulations (NAQMD) on electronically excited MoSe 2 bilayers reproduce the observed picosecond-scale increase in lattice temperature and ultrafast conversion of photoenergy to lattice vibrations. Calculation of excited-state phonon dispersion curves suggests that softened vibrational modes in the excited state are involved in efficient and rapid energy

Ultrafast non-radiative dynamics of atomically thin MoSe 2

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lin, Ming -Fu; Kochat, Vidya; Krishnamoorthy, Aravind

Non-radiative energy dissipation in photoexcited materials and resulting atomic dynamics provide a promising pathway to induce structural phase transitions in two-dimensional materials. However, these dynamics have not been explored in detail thus far because of incomplete understanding of interaction between the electronic and atomic degrees of freedom, and a lack of direct experimental methods to quantify real-time atomic motion and lattice temperature. Here, we explore the ultrafast conversion of photoenergy to lattice vibrations in a model bi-layered semiconductor, molybdenum diselenide, MoSe 2. Specifically, we characterize sub-picosecond lattice dynamics initiated by the optical excitation of electronic charge carriers in the highmore » electron-hole plasma density regime. Our results focuses on the first ten picosecond dynamics subsequent to photoexcitation before the onset of heat transfer to the substrate, which occurs on a ~100 picosecond time scale. Photoinduced atomic motion is probed by measuring the time dependent Bragg diffraction of a delayed mega-electronvolt femtosecond electron beam. Transient lattice temperatures are characterized through measurement of Bragg peak intensities and calculation of the Debye-Waller factor (DWF). These measurements show a sub-picosecond decay of Bragg diffraction and a correspondingly rapid rise in lattice temperatures. We estimate a high quantum yield for the conversion of excited charge carrier energy to lattice motion under our experimental conditions, indicative of a strong electron-phonon interaction. First principles nonadiabatic quantum molecular dynamics simulations (NAQMD) on electronically excited MoSe 2 bilayers reproduce the observed picosecond-scale increase in lattice temperature and ultrafast conversion of photoenergy to lattice vibrations. Calculation of excited-state phonon dispersion curves suggests that softened vibrational modes in the excited state are involved in efficient and rapid energy

Spacecraft thermal energy accommodation from atomic recombination

NASA Technical Reports Server (NTRS)

Carleton, Karen L.; Marinelli, William J.

1991-01-01

Measurements of atomic recombination probabilities important in determining energy release to reusable spacecraft thermal protection surfaces during reentry are presented. An experimental apparatus constructed to examine recombination of atomic oxygen from thermal protection and reference materials at reentry temperatures is described. The materials are examined under ultrahigh vacuum conditions to develop and maintain well characterized surface conditions that are free of contamination. When compared with stagnation point heat transfer measurements performed in arc jet facilities, these measurements indicate that a significant fraction of the excess energy available from atom recombination is removed from the surface as metastable O2.

Electron- and photon-stimulated desorption of atomic hydrogen from radiation-modified alkali halide surfaces

NASA Astrophysics Data System (ADS)

Hudson, L. T.; Tolk, N. H.; Bao, C.; Nordlander, P.; Russell, D. P.; Xu, J.

2000-10-01

The desorption yields of excited hydrogen atoms from the surfaces of KCl, KBr, NaCl, NaF, and LiF have been measured as a function of incident photon and electron energy and flux, time of irradiation, dosing pressure of H2 and sample temperature. As these surfaces are exposed to H2 gas during electron or photon bombardment, the fluorescence from excited hydrogen atoms ejected from the surface is monitored. The desorption yields are found to be contingent upon surface damage induced by the incident particle radiation, leading to dissociative adsorption at surface sites containing an excess of alkali metal. A desorption mechanism is presented in which incident electrons or photons induce a valence excitation to a neutral, antibonding state of the surface alkali hydride molecule complex, leading to the desorption of hydrogen atoms possessing several eV of kinetic energy.

Atomic Mass and Nuclear Binding Energy for U-287 (Uranium)

NASA Astrophysics Data System (ADS)

Sukhoruchkin, S. I.; Soroko, Z. N.

This document is part of the Supplement containing the complete sets of data of Subvolume B `Nuclei with Z = 55 - 100' of Volume 22 `Nuclear Binding Energies and Atomic Masses' of Landolt-Börnstein - Group I `Elementary Particles, Nuclei and Atoms', and additionally including data for nuclei with Z = 101 - 130. It provides atomic mass, mass excess, nuclear binding energy, nucleon separation energies, Q-values, and nucleon residual interaction parameters for atomic nuclei of the isotope U-287 (Uranium, atomic number Z = 92, mass number A = 287).

Atomic Mass and Nuclear Binding Energy for Ac-212 (Actinium)

NASA Astrophysics Data System (ADS)

Sukhoruchkin, S. I.; Soroko, Z. N.

This document is part of the Supplement containing the complete sets of data of Subvolume B `Nuclei with Z = 55 - 100' of Volume 22 `Nuclear Binding Energies and Atomic Masses' of Landolt-Börnstein - Group I `Elementary Particles, Nuclei and Atoms', and additionally including data for nuclei with Z = 101 - 130. It provides atomic mass, mass excess, nuclear binding energy, nucleon separation energies, Q-values, and nucleon residual interaction parameters for atomic nuclei of the isotope Ac-212 (Actinium, atomic number Z = 89, mass number A = 212).

Singlet-triplet splittings from the virial theorem and single-particle excitation energies

NASA Astrophysics Data System (ADS)

Becke, Axel D.

2018-01-01

The zeroth-order (uncorrelated) singlet-triplet energy difference in single-particle excited configurations is 2Kif, where Kif is the Coulomb self-energy of the product of the transition orbitals. Here we present a non-empirical, virial-theorem argument that the correlated singlet-triplet energy difference should be half of this, namely, Kif. This incredibly simple result gives vertical HOMO-LUMO excitation energies in small-molecule benchmarks as good as the popular TD-B3LYP time-dependent approach to excited states. For linear acenes and nonlinear polycyclic aromatic hydrocarbons, the performance is significantly better than TD-B3LYP. In addition to the virial theorem, the derivation borrows intuitive pair-density concepts from density-functional theory.

Electron-impact ionization cross sections out of the ground and 6P2 excited states of cesium

NASA Astrophysics Data System (ADS)

Łukomski, M.; Sutton, S.; Kedzierski, W.; Reddish, T. J.; Bartschat, K.; Bartlett, P. L.; Bray, I.; Stelbovics, A. T.; McConkey, J. W.

2006-09-01

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 6P3/22 state between 7eV and 400eV . 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 (<11eV) 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.

Excited state conformational dynamics in carotenoids: dark intermediates and excitation energy transfer.

PubMed

Beck, Warren F; Bishop, Michael M; Roscioli, Jerome D; Ghosh, Soumen; Frank, Harry A

2015-04-15

A consideration of the excited state potential energy surfaces of carotenoids develops a new hypothesis for the nature of the conformational motions that follow optical preparation of the S2 (1(1)Bu(+)) state. After an initial displacement from the Franck-Condon geometry along bond length alternation coordinates, it is suggested that carotenoids pass over a transition-state barrier leading to twisted conformations. This hypothesis leads to assignments for several dark intermediate states encountered in femtosecond spectroscopic studies. The Sx state is assigned to the structure reached upon the onset of torsional motions near the transition state barrier that divides planar and twisted structures on the S2 state potential energy surface. The X state, detected recently in two-dimensional electronic spectra, corresponds to a twisted structure well past the barrier and approaching the S2 state torsional minimum. Lastly, the S(∗) state is assigned to a low lying S1 state structure with intramolecular charge transfer character (ICT) and a pyramidal conformation. It follows that the bent and twisted structures of carotenoids that are found in photosynthetic light-harvesting proteins yield excited-state structures that favor the development of an ICT character and optimized energy transfer yields to (bacterio)chlorophyll acceptors. Copyright © 2015 Elsevier Inc. All rights reserved.

Semiclassical quantization of Bohr orbits in the helium atom

NASA Astrophysics Data System (ADS)

Belov, V. V.; Maksimov, V. A.

2007-05-01

We use the complex WKB-Maslov method to construct the semiclassical spectral series corresponding to the resonance Bohr orbits in the helium atom. The semiclassical energy levels represented as the Rydberg tetra series correspond to the doubly symmetrically excited states of helium-like atoms. This level series contains the Rydberg triple series reported by Richter and Wintgen in 1991, which corresponds to the Z2+e-e- configuration of electrons observed by Eichmann and his collaborators in experiments on the laser excitation of the barium atom in 1992. The lower-level extrapolation of the formula obtained for the semiclassical spectrum gives the value of the ground state energy, which differs by 6% from the experimental value obtained by Bergeson and his collaborators in 1998. We also calculate the fine structure of the semiclassical spectrum due to the spin-orbit and spin-spin interactions of electrons.

L-dependence of low energy spin excitations in FeTe/Se superconductors

NASA Astrophysics Data System (ADS)

Xu, Guangyong; Xu, Zhijun; Schneeloch, John; Wen, Jinsheng; Winn, Barry; Zhao, Yang; Birgeneau, Robert; Gu, Genda; Tranquada, John

We will present neutron scattering measurements on low energy magnetic excitations from FeTe1-xSex (``11'' system) samples. Our work shows that the low energy magnetic excitations are dominated by 2D correlations in the superconducting (SC) compound at low temperature, with the L-dependence well described by the Fe magnetic form factor. However, at temperatures much higher than TC, the magnetic excitations become more three-dimensional with a clear change in the L-dependence. The low energy magnetic excitations from non-superconducting (NSC) samples, on the other hand, always exhibit three-dimensional features for the entire temperature range of our measurements. Our results suggest that in additional to in-plane correlations, the inter-plane spin correlations are also coupled to the superconducting properties in the ``11'' system.

Modal energy analysis for mechanical systems excited by spatially correlated loads

NASA Astrophysics Data System (ADS)

Zhang, Peng; Fei, Qingguo; Li, Yanbin; Wu, Shaoqing; Chen, Qiang

2018-10-01

MODal ENergy Analysis (MODENA) is an energy-based method, which is proposed to deal with vibroacoustic problems. The performance of MODENA on the energy analysis of a mechanical system under spatially correlated excitation is investigated. A plate/cavity coupling system excited by a pressure field is studied in a numerical example, in which four kinds of pressure fields are involved, which include the purely random pressure field, the perfectly correlated pressure field, the incident diffuse field, and the turbulent boundary layer pressure fluctuation. The total energies of subsystems differ to reference solution only in the case of purely random pressure field and only for the non-excited subsystem (the cavity). A deeper analysis on the scale of modal energy is further conducted via another numerical example, in which two structural modes excited by correlated forces are coupled with one acoustic mode. A dimensionless correlation strength factor is proposed to determine the correlation strength between modal forces. Results show that the error on modal energy increases with the increment of the correlation strength factor. A criterion is proposed to establish a link between the error and the correlation strength factor. According to the criterion, the error is negligible when the correlation strength is weak, in this situation the correlation strength factor is less than a critical value.

Cs 62 DJ Rydberg-atom macrodimers formed by long-range multipole interaction

NASA Astrophysics Data System (ADS)

Han, Xiaoxuan; Bai, Suying; Jiao, Yuechun; Hao, Liping; Xue, Yongmei; Zhao, Jianming; Jia, Suotang; Raithel, Georg

2018-03-01

Long-range macrodimers formed by D -state cesium Rydberg atoms are studied in experiments and calculations. Cesium [62DJ]2 Rydberg-atom macrodimers, bonded via long-range multipole interaction, are prepared by two-color photoassociation in a cesium atom trap. The first color (pulse A) resonantly excites seed Rydberg atoms, while the second (pulse B, detuned by the molecular binding energy) resonantly excites the Rydberg-atom macrodimers below the [62DJ]2 asymptotes. The molecules are measured by extraction of autoionization products and Rydberg-atom electric-field ionization, and ion detection. Molecular spectra are compared with calculations of adiabatic molecular potentials. From the dependence of the molecular signal on the detection delay time, the lifetime of the molecules is estimated to be 3 -6 μ s .

Identification of the low-energy excitations in a quantum critical system

NASA Astrophysics Data System (ADS)

Heitmann, Tom; Lamsal, Jagat; Watson, Shannon; Erwin, Ross; Chen, Wangchun; Zhao, Yang; Montfrooij, Wouter

2017-05-01

We have identified low-energy magnetic excitations in a doped quantum critical system by means of polarized neutron scattering experiments. The presence of these excitations could explain why Ce(Fe0.76Ru0.24)2Ge2 displays dynamical scaling in the absence of local critical behavior or long-range spin-density wave criticality. The low-energy excitations are associated with the reorientations of the superspins of fully ordered, isolated magnetic clusters that form spontaneously upon lowering the temperature. The system houses both frozen clusters and dynamic clusters, as predicted by Hoyos and Vojta [Phys. Rev. B 74, 140401(R) (2006)].

Damping of Bogoliubov excitations in optical lattices

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tsuchiya, Shunji; Department of Physics, Waseda University, 3-4-1 Okubo, Tokyo 169-8555; Griffin, Allan

2004-08-01

Extending recent work to finite temperatures, we calculate the Landau damping of a Bogoliubov excitation in an optical lattice, due to the coupling to a thermal cloud of such excitations. For simplicity, we consider a one-dimensional Bose-Hubbard model and restrict ourselves to the first energy band. For energy conservation to be satisfied, the excitations in the collision processes must exhibit ''anomalous dispersion,'' analogous to phonons in superfluid {sup 4}He. This leads to the disappearance of all damping processes when Un{sup c0}{>=}6J, where U is the on-site interaction, J is the hopping matrix element, and n{sup c0}(T) is the number ofmore » condensate atoms at a lattice site. This phenomenon also occurs in two-dimensional and three-dimensional optical lattices. The disappearance of Beliaev damping above a threshold wave vector is noted.« less

Excitation energies, radiative and autoionization rates, dielectronic satellite lines, and dielectronic recombination rates for excited states of Rb-like W from Kr-like W [Relativistic atomic data for Rb-like tungsten

DOE PAGES

Safronova, U. I.; Safronova, A. S.; Beiersdorfer, P.

2016-11-02

Energy levels, radiative transition probabilities, and autoionization rates for [Ni]more » $$4{s}^{2}4{p}^{6}{nl}$$, [Ni]$$4{s}^{2}4{p}^{5}4l^{\\prime} {nl}$$ ($$l^{\\prime} =d,f,n$$ = 4–7), [Ni]$$4s4{p}^{6}4l^{\\prime} {nl}$$, ($$l^{\\prime} =d,f,n$$ = 4–7), [Ni]$$4{s}^{2}4{p}^{5}5l^{\\prime} {nl}$$ (n = 5–7), and [Ni]$$4s4{p}^{6}6l^{\\prime} {nl}$$ (n = 6–7) states in Rb-like tungsten (W37+) are calculated using the relativistic many-body perturbation theory method (RMBPT code) and the Hartree–Fock-relativistic method (COWAN code). Autoionizing levels above the [Ni]$$4{s}^{2}4{p}^{6}$$ threshold are considered. It is found that configuration mixing among [Ni]$$4{s}^{2}4{p}^{5}4l^{\\prime} {nl}$$ and [Ni]$$4s4{p}^{6}4l^{\\prime} {nl}$$ plays an important role for all atomic characteristics. Branching ratios relative to the first threshold and intensity factors are calculated for satellite lines, and dielectronic recombination (DR) rate coefficients are determined for the [Ni]$$4{s}^{2}4{p}^{6}{nl}$$ (n = 4–7) singly excited states, as well as the [Ni]$$4{s}^{2}4{p}^{5}4{dnl}$$, [Ni]$$4{s}^{2}4{p}^{5}4{fnl}$$, [Ni]$$4s4{p}^{6}4{dnl}$$, [Ni]$$4{s}^{2}4{p}^{6}4{fnl}$$, (n = 4–6), and [Ni]$$4{s}^{2}4{p}^{5}5l^{\\prime} 5l$$ doubly excited nonautoionizing states in Rb-like W37+ ion. Contributions from the [Ni]$$4s24{p}^{6}4{fnl}$$ (n = 6–7), [Ni]$$4{s}^{2}4{p}^{5}5l^{\\prime} {nl}$$ (n = 5–6), and [Ni]$$4{s}^{2}4{p}^{5}6l^{\\prime} {nl}$$ (n = 6–7) doubly excited autoionizing states are evaluated numerically. The high-n state (with n up to 500) contributions are very important for high temperatures. These contributions are determined by using a scaling procedure. Synthetic dielectronic satellite spectra from Rb-like W are simulated in a broad spectral range from 8 to 70 Å. Here, these calculations provide highly accurate values for a number of W 37+ properties useful for a variety of applications including for fusion applications.« less

K-shell excitation studied for H- and He-like bismuth ions in collisions with low-Z target atoms

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stoehlker, T.; Ionescu, D.C.; Rymuza, P.

1998-02-01

The formation of excited projectile states via Coulomb excitation is investigated for hydrogenlike and heliumlike bismuth projectiles (Z=83) in relativistic ion-atom collisions. The excitation process was unambiguously identified by observing the radiative decay of the excited levels to the vacant 1s shell in coincidence with ions that did not undergo charge exchange in the reaction target. In particular, owing to the large fine-structure splitting of Bi, the excitation cross sections to the various L-shell sublevels are determined separately. The results are compared with detailed relativistic calculations, showing that both the relativistic character of the bound-state wave functions and the magneticmore » interaction are of considerable importance for the K-shell excitation process in high-Z ions such as Bi. The experimental data confirm the result of the complete relativistic calculations, namely, that the magnetic part of the Li{acute e}nard-Wiechert interaction leads to a significant reduction of the K-shell excitation cross section. {copyright} {ital 1998} {ital The American Physical Society}« less

Excitations in confined helium

NASA Astrophysics Data System (ADS)

Apaja, V.; Krotscheck, E.

2003-05-01

We design models for helium in matrices such as aerogel, Vycor, or Geltech from a manifestly microscopic point of view. For that purpose, we calculate the dynamic structure function of 4He on Si substrates and between two Si walls as a function of energy, momentum transfer, and the scattering angle. The angle-averaged results are in good agreement with the neutron scattering data; the remaining differences can be attributed to the simplified model used here for the complex pore structure of the materials. A focus of the present work is the detailed identification of coexisting layer modes and bulklike excitations, and, in the case of thick films, ripplon excitations. Involving essentially two-dimensional motion of atoms, the layer modes are sensitive to the scattering angle.

Solvation and Spectral Line Shifts of Chromium Atoms in Helium Droplets Based on a Density Functional Theory Approach

PubMed Central

2014-01-01

The interaction of an electronically excited, single chromium (Cr) atom with superfluid helium nanodroplets of various size (10 to 2000 helium (He) atoms) is studied with helium density functional theory. Solvation energies and pseudo-diatomic potential energy surfaces are determined for Cr in its ground state as well as in the y7P, a5S, and y5P excited states. The necessary Cr–He pair potentials are calculated by standard methods of molecular orbital-based electronic structure theory. In its electronic ground state the Cr atom is found to be fully submerged in the droplet. A solvation shell structure is derived from fluctuations in the radial helium density. Electronic excitations of an embedded Cr atom are simulated by confronting the relaxed helium density (ρHe), obtained for Cr in the ground state, with interaction pair potentials of excited states. The resulting energy shifts for the transitions z7P ← a7S, y7P ← a7S, z5P ← a5S, and y5P ← a5S are compared to recent fluorescence and photoionization experiments. PMID:24906160

Solvation and spectral line shifts of chromium atoms in helium droplets based on a density functional theory approach.

PubMed

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

2014-08-21

The interaction of an electronically excited, single chromium (Cr) atom with superfluid helium nanodroplets of various size (10 to 2000 helium (He) atoms) is studied with helium density functional theory. Solvation energies and pseudo-diatomic potential energy surfaces are determined for Cr in its ground state as well as in the y(7)P, a(5)S, and y(5)P excited states. The necessary Cr-He pair potentials are calculated by standard methods of molecular orbital-based electronic structure theory. In its electronic ground state the Cr atom is found to be fully submerged in the droplet. A solvation shell structure is derived from fluctuations in the radial helium density. Electronic excitations of an embedded Cr atom are simulated by confronting the relaxed helium density (ρHe), obtained for Cr in the ground state, with interaction pair potentials of excited states. The resulting energy shifts for the transitions z(7)P ← a(7)S, y(7)P ← a(7)S, z(5)P ← a(5)S, and y(5)P ← a(5)S are compared to recent fluorescence and photoionization experiments.

High energy photons excited photodynamic cancer therapy in vitro

NASA Astrophysics Data System (ADS)

Guo, Yiping; Sheng, Shi; Zhang, Wei; Lun, Michael; Tsai, Shih-Ming; Chin, Wei-Chun; Hoglund, Roy; Li, Changqing

2018-02-01

Photodynamic therapy (PDT) is a noninvasive phototherapy method that has been clinically approved for many years. During this type of therapy, the photosensitizing agent will be excited by optical photons to generate reactive oxygen species which can kill nearby cancer cells. However, due to the strong optical scattering and absorption of tissue, optical photons can only penetrate tissues in few millimeters which result in the limited applications of PDT to superficial lesions like skin cancers. In this study, to overcome the penetration limitations, we used high-energy photons to excite photosensitizers directly by assuming that high-energy photons generate low-energy optical photons in tissues to excite photosensitizers. Cesium- 137 irradiator has been used as the high-energy photon source. A fiber pigtailed diode laser was used to validate the photosensitizer's efficacy. We used MPPa as the photosensitizer to treat A549 cancer cell line with different concentrations of drug (10μM/ ml, 5 μM/ml, 2.5 μM/ml, 1 μM/ml and 0 μM/ml). We have performed an irradiation experiment for different time durations of 30 min, 15 min, 7 min to 3 min, respectively, and we also compared different drug concentrations and different exposure durations. Our study not only proved the MPPa PDT method was effective, but also indicated that high-energy photons enhanced PDT could potentially overcome the penetration limitations thus making PDT feasible for deep tissue cancer.

Ground Levels and Ionization Energies for the Neutral Atoms

National Institute of Standards and Technology Data Gateway

SRD 111 Ground Levels and Ionization Energies for the Neutral Atoms (Web, free access)   Data for ground state electron configurations and ionization energies for the neutral atoms (Z = 1-104) including references.

Spectroscopy of the three-photon laser excitation of cold Rubidium Rydberg atoms in a magneto-optical trap

DOE Office of Scientific and Technical Information (OSTI.GOV)

Entin, V. M.; Yakshina, E. A.; Tretyakov, D. B.

2013-05-15

The spectra of the three-photon laser excitation 5S{sub 1/2} {yields} 5P{sub 3/2} {yields} 6S{sub 1/2}nP of cold Rb Rydberg atoms in an operating magneto-optical trap based on continuous single-frequency lasers at each stage are studied. These spectra contain two partly overlapping peaks of different amplitudes, which correspond to coherent three-photon excitation and incoherent three-step excitation due to the presence of two different ways of excitation through the dressed states of intermediate levels. A four-level theoretical model based on optical Bloch equations is developed to analyze these spectra. Good agreement between the experimental and calculated data is achieved by introducing additionalmore » decay of optical coherence induced by a finite laser line width and other broadening sources (stray electromagnetic fields, residual Doppler broadening, interatomic interactions) into the model.« less

Femtosecond Time-Resolved Photoelectron Imaging of Excited Doped Helium Nanodroplets

NASA Astrophysics Data System (ADS)

Saladrigas, Catherine; Bacellar, Camila; Leone, Stephen R.; Neumark, Daniel M.; Gessner, Oliver

2017-04-01

Helium nanodroplets are excellent matrices for high resolution spectroscopy and the study of ultracold chemistry. They are optically transparent. In their electronic ground state, interact very weakly with any atomic or molecular dopant. Electronically excited droplets, however, can strongly interact with dopants through a variety of relaxation mechanisms. Previously, these host-dopant interactions were studied in the energy domain, revealing Penning ionization processes enabled by energy transfer between the droplet host and atomic dopants. Using femtosecond time resolved XUV photoelectron imaging, we plan to perform complementary experiments in the time domain to gain deeper insight into the timescales of energy transfer processes and how they compete with internal droplet relaxation. First experiments will be performed using noble gas dopants, such as Kr and Ne, which will be compared to previous energy-domain studies. Femtosecond XUV pulses produced by high harmonic generation will be used to excite the droplets, IR and near-UV light will be used to monitor the relaxation dynamics. Using velocity map imaging, both photoelectron kinetic energies and angular distributions will be recorded as a function of time. Preliminary results and proposed experiments will be presented.

Induced dipole-dipole coupling between two atoms at a migration resonance

NASA Astrophysics Data System (ADS)

Kaur, Maninder; Mian, Mahmood

2018-05-01

Results of numerical simulations for the resonant energy exchange phenomenon called Migration reaction between two cold Rydberg atoms are presented. The effect of spatial interatomic distance on the onset of peculiar coherent mechanism is investigated. Observation of Rabi-like population inversion oscillation at the resonance provides a clear signature of dipole induced exchange of electronic excitations between the atoms. Further we present the results for the dependence of expectation value of the interaction hamiltonian on the interatomic distance, which is responsible for energy exchange process. The results of this observation endorse the range of inter atomic distance within which the excitation exchange process occurs completely or partially. Migration process enhance the Rydberg-Rydberg interaction in the absence of an external field, under the condition of the zero permanent dipole moments. Our next observation sheds light on the fundamental mechanism of induced electric fields initiated by the oscillating dipoles in such energy exchange processes. We explore the dependence of induced electric field on the interatomic distance and angle between the dipoles highlighting the inverse power law dependence and anisotropic property of the field. We put forward an idea to utilise the coherent energy exchange process to build efficient and fast energy transfer channels by incorporating more atoms organised at successive distances with decreasing distance gradient.

The reaction efficiency of thermal energy oxygen atoms with polymeric materials

NASA Technical Reports Server (NTRS)

Koontz, S. L.; Nordine, Paul

1990-01-01

The reaction efficiency of several polymeric materials with thermal-energy (0.04 eV translational energy), ground-state (O3P) oxygen atoms was determined by exposing the materials to a room temperature gas containing a known concentration of atomic oxygen. The reaction efficiency measurements were conducted in two flowing afterglow systems of different configuration. Atomic oxygen concentration measurements, flow, transport and surface dose analysis is presented in this paper. The measured reaction efficiencies of Kapton, Mylar, polyethylene, D4-polyethylene and Tedlar are .001 to .0001 those determined with high-energy ground-state oxygen atoms in low earth orbit or in a high-velocity atom beam. D4-polyethylene exhibits a large kinetic isotope effect with atomic oxygen at thermal but not hyperthermal atom energies.

Measurements and kinetic modeling of atomic species in fuel-oxidizer mixtures excited by a repetitive nanosecond pulse discharge

NASA Astrophysics Data System (ADS)

Winters, C.; Eckert, Z.; Yin, Z.; Frederickson, K.; Adamovich, I. V.

2018-01-01

This work presents the results of number density measurements of metastable Ar atoms and ground state H atoms in diluted mixtures of H2 and O2 with Ar, as well as ground state O atoms in diluted H2-O2-Ar, CH4-O2-Ar, C3H8-O2-Ar, and C2H4-O2-Ar mixtures excited by a repetitive nanosecond pulse discharge. The measurements have been made in a nanosecond pulse, double dielectric barrier discharge plasma sustained in a flow reactor between two plane electrodes encapsulated within dielectric material, at an initial temperature of 500 K and pressures ranging from 300 Torr to 700 Torr. Metastable Ar atom number density distribution in the afterglow is measured by tunable diode laser absorption spectroscopy, and used to characterize plasma uniformity. Temperature rise in the reacting flow is measured by Rayleigh scattering. H atom and O atom number densities are measured by two-photon absorption laser induced fluorescence. The results are compared with kinetic model predictions, showing good agreement, with the exception of extremely lean mixtures. O atoms and H atoms in the plasma are produced mainly during quenching of electronically excited Ar atoms generated by electron impact. In H2-Ar and O2-Ar mixtures, the atoms decay by three-body recombination. In H2-O2-Ar, CH4-O2-Ar, and C3H8-O2-Ar mixtures, O atoms decay in a reaction with OH, generated during H atom reaction with HO2, with the latter produced by three-body H atom recombination with O2. The net process of O atom decay is O  +  H  →  OH, such that the decay rate is controlled by the amount of H atoms produced in the discharge. In extra lean mixtures of propane and ethylene with O2-Ar the model underpredicts the O atom decay rate. At these conditions, when fuel is completely oxidized by the end of the discharge burst, the net process of O atom decay, O  +  O  →  O2, becomes nearly independent of H atom number density. Lack of agreement with the data at these conditions is

Research on the properties and interactions of simple atomic and ionic systems

NASA Technical Reports Server (NTRS)

Novick, R.

1972-01-01

Simple ionic systems were studied, such as metastable autoionizing states of the negative He ion, two-photon decay spectrum of metastable He ion, optical excitation with low energy ions, and lifetime measurements of singly ionized Li and metastable He ion. Simple atomic systems were also investigated. Metastable autoionizing atomic energy levels in alkali elements were included, along with lifetime measurements of Cr-53, group 2A isotopes, and alkali metal atoms using level crossing and optical double resonance spectroscopy.

JANUS — A setup for low-energy Coulomb excitation at ReA3

DOE PAGES

Lunderberg, E.; Belarge, J.; Bender, P. C.; ...

2017-12-21

We report that a new experimental setup for low-energy Coulomb excitation experiments was constructed in a collaboration between the National Superconducting Cyclotron Laboratory (NSCL), Lawrence Livermore National Laboratory (LLNL), and the University of Rochester and was commissioned at the general purpose beam line of NSCL's ReA3 reaccelerator facility. The so-called JANUS setup combines γ-ray detection with the Segmented Ge Array (SeGA) and scattered particle detection using a pair of segmented double-sided Si detectors (Bambino 2). The low-energy Coulomb excitation program that JANUS enables will complement intermediate-energy Coulomb excitation studies that have long been performed at NSCL by providing access tomore » observables that quantify collectivity beyond the first excited state, including the sign and magnitude of excited-state quadrupole moments. Here, in this work, the setup and its performance will be described based on the commissioning run that used stable 78Kr impinging onto a 1.09 mg/cm 2 208Pb target at a beam energy of 3.9 MeV/u.« less

Experimental evaluation of analyte excitation mechanisms in the inductively coupled plasma

NASA Astrophysics Data System (ADS)

Lehn, Scott A.; Hieftje, Gary M.

2003-10-01

The inductively coupled plasma (ICP) is a justifiably popular source for atomic emission spectrometry. However, despite its popularity, the ICP is still only partially understood. Even the mechanisms of analyte excitation remain unclear; some energy levels are quite clearly populated by charge transfer while others might be populated by electron-ion recombination, by electron impact, or by Penning processes. Distinguishing among these alternatives is possible by means of a steady-state kinetics approach that examines correlations between the emission of a selected atom, ion, or level and the local number densities of species assumed to produce the excitation. In an earlier investigation, strong correlations were found between either calcium atom or ion emission and selected combinations of calcium atom or ion number densities and electron number densities in the plasma. However, all radially resolved data employed in the earlier study were produced from Abel inversion and from measurements that were crude by today's standards. Now, by means of tomographic imaging, laser-saturated atomic fluorescence, and Thomson and Rayleigh scattering, it is possible to measure the required radially resolved data without Abel inversion and with far greater fidelity. The correlations previously studied for calcium have been investigated with these more reliable data. Ion-electron recombination, either radiative or with argon as a third body, was determined to be the most likely excitation mechanism for calcium atom, while electron impact appeared to be the most important process to produce excite-state calcium ions. These results were consistent with the previous study. However, the present study suggests that collisional deactivation, rather than radiative decay, is the most likely mode of returning both calcium atoms and ions to the ground state.

Kinetics of plasma formation in sodium vapor excited by nanosecond resonant laser pulses

NASA Astrophysics Data System (ADS)

Mahmoud, M. A.; Gamal, Y. E. E.

2012-07-01

We have studied theoretically formation of molecular ion Na2 + and the atomic ion Na+ which are created in laser excited sodium vapor at the first resonance transition, 3S1/2-3P1/2. A set of rate equations, which describe the temporal variation of the electron energy distribution function (EEDF), the electron density, the population density of the excited states as well as the atomic Na+ and molecular ion Na2 +, are solved numerically. The calculations are carried out at different laser energy and different sodium atomic vapor densities. The numerical calculations of the EEDF show that a deviation from the Maxwellian distribution due to the superelastic collisions effect. In addition to the competition between associative ionization (3P-3P), associative ionization (3P-3D) and Molnar-Hornbeck ionization processes for producing Na2 +, the calculations have also shown that the atomic ions Na+ are formed through the Penning ionization and photoionization processes. These results are found to be consistent with the experimental observations.

Matrix-Assisted Plasma Atomization Emission Spectrometry for Surface Sampling Elemental Analysis

PubMed Central

Yuan, Xin; Zhan, Xuefang; Li, Xuemei; Zhao, Zhongjun; Duan, Yixiang

2016-01-01

An innovative technology has been developed involving a simple and sensitive optical spectrometric method termed matrix-assisted plasma atomization emission spectrometry (MAPAES) for surface sampling elemental analysis using a piece of filter paper (FP) for sample introduction. MAPAES was carried out by direct interaction of the plasma tail plume with the matrix surface. The FP absorbs energy from the plasma source and releases combustion heating to the analytes originally present on its surface, thus to promote the atomization and excitation process. The matrix-assisted plasma atomization excitation phenomenon was observed for multiple elements. The FP matrix served as the partial energy producer and also the sample substrate to adsorb sample solution. Qualitative and quantitative determinations of metal ions were achieved by atomic emission measurements for elements Ba, Cu, Eu, In, Mn, Ni, Rh and Y. The detection limits were down to pg level with linear correlation coefficients better than 0.99. The proposed MAPAES provides a new way for atomic spectrometry which offers advantages of fast analysis speed, little sample consumption, less sample pretreatment, small size, and cost-effective. PMID:26762972

Accurate atomic data for xenon: energy levels, oscillator strengths, and electron collision cross sections

NASA Astrophysics Data System (ADS)

Bartschat, Klaus; Zatsarinny, Oleg

2009-10-01

We have applied our recently developed fully relativistic Dirac B-spline R-matrix (DBSR) code [1] to calculate the atomic structure (energy levels and oscillator strengths) as well as electron scattering from xenon atoms. Results from a 31-state close-coupling model for the excitation function of the metastable (5p^5 6s) J=0,2 states show excellent agreement with experiment [2], thereby presenting a significant improvement over the most sophisticated previous Breit-Pauli calculations [3,4]. The same model is currently being used to calculate electron-impact excitation from the metastable J=2 state. The results will be compared with recent experimental data [5] and predictions from other theoretical models [6,7]. Our dataset is an excellent basis for modeling plasma discharges containing xenon.[0pt] [1] O. Zatsarinny and K. Bartschat, Phys. Rev. A 77 (2008) 062701.[0pt] [2] S. J. Buckman et al., J. Phys. B 16 (1983) 4219.[0pt] [3] A. N. Grum-Grzhimailo and K. Bartschat, J. Phys. B 35 (2002) 3479.[0pt] [4] M. Allan et al., Phys. Rev. A 74 (2006) 030701(R).[0pt] [5] R. O. Jung et al., Phys. Rev. A 72 (2005) 022723.[0pt] [6] R. Srivastava et al., Phys. Rev. A 74 (2006) 012715.[0pt] [7] J. Jiang et al., J. Phys. B 41 (2008) 245204.

QED effects on individual atomic orbital energies

NASA Astrophysics Data System (ADS)

Kozioł, Karol; Aucar, Gustavo A.

2018-04-01

Several issues, concerning QED corrections, that are important in precise atomic calculations are presented. The leading QED corrections, self-energy and vacuum polarization, to the orbital energy for selected atoms with 30 ≤ Z ≤ 118 have been calculated. The sum of QED and Breit contributions to the orbital energy is analyzed. It has been found that for ns subshells the Breit and QED contributions are of comparative size, but for np and nd subshells the Breit contribution takes a major part of the QED+Breit sum. It has also, been found that the Breit to leading QED contributions ratio for ns subshells is almost independent of Z. The Z-dependence of QED and Breit+QED contributions per subshell is shown. The fitting coefficients may be used to estimate QED effects on inner molecular orbitals. We present results of our calculations for QED contributions to orbital energy of valence ns-subshell for group 1 and 11 atoms and discuss about the reliability of these numbers by comparing them with experimental first ionization potential data.

Electron capture in collisions of Al2+ ions with He atoms at intermediate energies

NASA Astrophysics Data System (ADS)

Watanabe, A.; Sato, H.; Gu, J. P.; Hirsch, G.; Buenker, R. J.; Kimura, M.

2001-09-01

Electron capture resulting from collisions of Al2+ ions with He atoms from 0.15 to 1000 keV/u is investigated using a molecular-orbital representation within a semiclassical frame. Molecular electronic states and corresponding couplings are determined by the ALCHEMY program. Sixteen molecular states all connecting to single-electron-capture processes are included, and hence radial and rotational couplings among these channels are fully considered. The trajectory effect arising from the straight-line, Coulomb, and ground-state potential trajectories for electron-capture and excitation processes is carefully assessed. The electron-capture cross section by ground-state Al2+(2S) ions slowly increases before it reaches a maximum of 1.3×10-16 cm2 at 100 keV/u. Those for metastable Al2+(2P) ions sharply increase with increasing energy, and reach a peak at 1 keV/u with a value of 1.5×10-16 cm2. The earlier experimental data are found to be larger by an order of magnitude although their energy dependence is in good accord with the present result. Excitation cross sections for both the ground and metastable states are found to be much larger by a factor of 2-3 than corresponding capture cross sections above 1 keV/u although they become comparable below this energy.

The Atomic Energy Commission's Annual Report to Congress for 1962. Major Activities in the Atomic Energy Programs, January - December 1962

DOE Office of Scientific and Technical Information (OSTI.GOV)

Seaborg, Glenn T.

1963-01-31

The document represents the 1962 Annual Report of the Atomic Energy Commission (AEC) to Congress. This year's report opens with a section of Highlights of the Atomic Energy Programs of 1962, followed by five parts: Part One, Commission Activities; Part Two, Nuclear Reactor Programs; Part Three, Production and Weapons Programs; Part Four, Other Major Programs; and Part Five, The Regulatory Program. Sixteen appendices are also included.

Excitation energy spectrum in helium II

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lu, P.; Chan, C.K.

1979-11-01

We obtain the roton part of the excitation energy spectrum in He II qualitatively. We point out that the distinct difference between this calculation and that of Parry and Ter Haar is that we do not use the Born approximation in the evaluation of t-matrix elements. We found that in addition to the contribution due to the hard-core part, the attractive potential helps to form the roton dip.

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.

Books on Atomic Energy for Adults and Children, Understanding the Atom Series.

ERIC Educational Resources Information Center

Atomic Energy Commission, Oak Ridge, TN. Div. of Technical Information.

This booklet in the "Understanding the Atom" series includes annotated bibliographies for children (grade level indicated) and adults. Over 100 basic books on atomic energy and closely related subjects are alphabetized by title and an author index. A list of publisher addresses are included. A brief introduction to library usage is given. The…

Thickness-dependent electron–lattice equilibration in laser-excited thin bismuth films

DOE PAGES

Sokolowski-Tinten, K.; Li, R. K.; Reid, A. H.; ...

2015-11-19

Electron–phonon coupling processes determine electronic transport properties of materials and are responsible for the transfer of electronic excess energy to the lattice. With decreasing device dimensions an understanding of these processes in nanoscale materials is becoming increasingly important. We use time-resolved electron diffraction to directly study energy relaxation in thin bismuth films after optical excitation. Precise measurements of the transient Debye–Waller-effect for various film thicknesses and over an extended range of excitation fluences allow to separate different contributions to the incoherent lattice response. While phonon softening in the electronically excited state is responsible for an immediate increase of the r.m.s.more » atomic displacement within a few hundred fs, 'ordinary' electron–phonon coupling leads to subsequent heating of the material on a few ps time-scale. Moreover, the data reveal distinct changes in the energy transfer dynamics which becomes faster for stronger excitation and smaller film thickness, respectively. The latter effect is attributed to a cross-interfacial coupling of excited electrons to phonons in the substrate.« less

Energy levels, radiative rates and electron impact excitation rates for transitions in He-like Ga XXX, Ge XXXI, As XXXII, Se XXXIII and Br XXXIV

NASA Astrophysics Data System (ADS)

Aggarwal, Kanti M.; Keenan, Francis P.

2013-04-01

We report calculations of energy levels, radiative rates and electron impact excitation cross sections and rates for transitions in He-like Ga XXX, Ge XXXI, As XXXII, Se XXXIII and Br XXXIV. The grasp (general-purpose relativistic atomic structure package) is adopted for calculating energy levels and radiative rates. For determining the collision strengths, and subsequently the excitation rates, the Dirac atomic R-matrix code (darc) is used. Oscillator strengths, radiative rates and line strengths are reported for all E1, E2, M1 and M2 transitions among the lowest 49 levels of each ion. Additionally, theoretical lifetimes are provided for all 49 levels of the above five ions. Collision strengths are averaged over a Maxwellian velocity distribution and the effective collision strengths obtained listed over a wide temperature range up to 108 K. Comparisons are made with similar data obtained using the flexible atomic code (fac) to highlight the importance of resonances, included in calculations with darc, in the determination of effective collision strengths. Discrepancies between the collision strengths from darc and fac, particularly for some forbidden transitions, are also discussed. Finally, discrepancies between the present results for effective collision strengths with the darc code and earlier semi-relativistic R-matrix data are noted over a wide range of electron temperatures for many transitions in all ions.

Surface conversion techniques for low energy neutral atom imagers

NASA Technical Reports Server (NTRS)

Quinn, J. M.

1995-01-01

This investigation has focused on development of key technology elements for low energy neutral atom imaging. More specifically, we have investigated the conversion of low energy neutral atoms to negatively charged ions upon reflection from specially prepared surfaces. This 'surface conversion' technique appears to offer a unique capability of detecting, and thus imaging, neutral atoms at energies of 0.01 - 1 keV with high enough efficiencies to make practical its application to low energy neutral atom imaging in space. Such imaging offers the opportunity to obtain the first instantaneous global maps of macroscopic plasma features and their temporal variation. Through previous in situ plasma measurements, we have a statistical picture of large scale morphology and local measurements of dynamic processes. However, with in situ techniques it is impossible to characterize or understand many of the global plasma transport and energization processes. A series of global plasma images would greatly advance our understanding of these processes and would provide the context for interpreting previous and future in situ measurements. Fast neutral atoms, created from ions that are neutralized in collisions with exospheric neutrals, offer the means for remotely imaging plasma populations. Energy and mass analysis of these neutrals provides critical information about the source plasma distribution. The flux of neutral atoms available for imaging depends upon a convolution of the ambient plasma distribution with the charge exchange cross section for the background neutral population. Some of the highest signals are at relatively low energies (well below 1 keV). This energy range also includes some of the most important plasma populations to be imaged, for example the base of the cleft ion fountain.

Low energy nuclear spin excitations in Ho metal investigated by high resolution neutron spectroscopy.

PubMed

Chatterji, Tapan; Jalarvo, Niina

2013-04-17

We have investigated the low energy excitations in metallic Ho by high resolution neutron spectroscopy. We found at T = 3 K clear inelastic peaks in the energy loss and energy gain sides, along with the central elastic peak. The energy of this low energy excitation, which is 26.59 ± 0.02 μeV at T = 3 K, decreased continuously and became zero at TN ≈ 130 K. By fitting the data in the temperature range 100-127.5 K with a power law we obtained the power-law exponent β = 0.37 ± 0.02, which agrees with the expected value β = 0.367 for a three-dimensional Heisenberg model. Thus the energy of the low energy excitations can be associated with the order parameter.

Growth kinetics for temperature-controlled atomic layer deposition of GaN using trimethylgallium and remote-plasma-excited NH3

NASA Astrophysics Data System (ADS)

Pansila, P.; Kanomata, K.; Miura, M.; Ahmmad, B.; Kubota, S.; Hirose, F.

2015-12-01

Fundamental surface reactions in the atomic layer deposition of GaN with trimethylgallium (TMG) and plasma-excited NH3 are investigated by multiple-internal-reflection infrared absorption spectroscopy (MIR-IRAS) at surface temperatures varying from room temperature (RT) to 400 °C. It is found that TMG is saturated at RT on GaN surfaces when the TMG exposure exceeds 8 × 104 Langmuir (L), where 1 L corresponds to 1.33 × 10-4 Pa s (or 1.0 × 10-6 Torr s), and its saturation density reaches the maximum value at RT. Nitridation with the plasma-excited NH3 on the TMG-saturated GaN surface is investigated by X-ray photoelectron spectroscopy (XPS). The nitridation becomes effective at surface temperatures in excess of 100 °C. The reaction models of TMG adsorption and nitridation on the GaN surface are proposed in this paper. Based on the surface analysis, a temperature-controlled ALD process consisting of RT-TMG adsorption and nitridation at 115 °C is examined, where the growth per cycle of 0.045 nm/cycle is confirmed. XPS analysis indicates that all N atoms are bonded as GaN. Atomic force microscopy indicates an average roughness of 0.23 nm. We discuss the reaction mechanism of GaN ALD in the low-temperature region at around 115 °C with TMG and plasma-excited NH3.

Advancing Efficient All-Electron Electronic Structure Methods Based on Numeric Atom-Centered Orbitals for Energy Related Materials

NASA Astrophysics Data System (ADS)

Blum, Volker

This talk describes recent advances of a general, efficient, accurate all-electron electronic theory approach based on numeric atom-centered orbitals; emphasis is placed on developments related to materials for energy conversion and their discovery. For total energies and electron band structures, we show that the overall accuracy is on par with the best benchmark quality codes for materials, but scalable to large system sizes (1,000s of atoms) and amenable to both periodic and non-periodic simulations. A recent localized resolution-of-identity approach for the Coulomb operator enables O (N) hybrid functional based descriptions of the electronic structure of non-periodic and periodic systems, shown for supercell sizes up to 1,000 atoms; the same approach yields accurate results for many-body perturbation theory as well. For molecular systems, we also show how many-body perturbation theory for charged and neutral quasiparticle excitation energies can be efficiently yet accurately applied using basis sets of computationally manageable size. Finally, the talk highlights applications to the electronic structure of hybrid organic-inorganic perovskite materials, as well as to graphene-based substrates for possible future transition metal compound based electrocatalyst materials. All methods described here are part of the FHI-aims code. VB gratefully acknowledges contributions by numerous collaborators at Duke University, Fritz Haber Institute Berlin, TU Munich, USTC Hefei, Aalto University, and many others around the globe.

The Stair-Step Atom.

ERIC Educational Resources Information Center

Jordan, Thomas M.; And Others

1992-01-01

Presents a model of a generic atom that is used to represent the movement of electrons from lower to higher levels and vice-versa due to excitation and de-excitation of the atom. As the process of de-excitation takes place, photons represented by colored ping-pong balls are emitted, indicating the emission of light. (MDH)

Excitations in the quantum liquid 4He: A review

NASA Astrophysics Data System (ADS)

Glyde, H. R.

2018-01-01

Progress made in measuring and interpreting the elementary excitations of superfluid and normal liquid {\\hspace{0pt}}^4He in the past 25 years is reviewed. The goal is to bring up to date the data, calculations and our understanding of the excitations since the books and reviews of the early 1990s. Only bulk liquid {\\hspace{0pt}}^4He is considered. Reference to liquid {\\hspace{0pt}}^3He , mixtures, reduced dimensions (films and confined helium) is made where useful to enhance interpretation. The focus is on the excitations as measured by inelastic neutron scattering methods. The review covers the dynamical response of liquid {\\hspace{0pt}}^4He from the collective excitations at low energy and long wavelength (i.e. phonon-roton modes) to the single particle excitations at high energy from which the atomic momentum distribution and Bose-Einstein condensate fraction are determined. A goal is to show the interplay of these excitations with other spectacular properties such as superfluidity and the test of fundamental calculations of quantum liquids that is possible. The role of Bose-Einstein condensation in determining the nature of the \

Coulomb excitation with radioactive nuclear beam of 64Cu

NASA Astrophysics Data System (ADS)

Guo, Gang; Xu, Jincheng; Chen, Quan; He, Ming; Qin, Jiuchang; Shen, Dongjun; Wu, Shaoyong; Jiang, Yongliang; Cheng, Yehao

2003-09-01

The radioactive nuclear beam of 64Cu was obtained utilizing a two-stage method at the HI-13 tandem accelerator of China Institute of Atomic Energy. The B(E2) value of the first excitation state of 64Cu has been directly measured for the first time by Coulomb excitation method, using the radioactive nuclear beam of 64Cu. An upper limit of the B(E2;2 1+→1 gs+) value from the first excitation state to the ground state of 64Cu is determined to be 49 W.u., which is significantly smaller than 250±170 W.u., the value adopted by Nuclear Data Sheets. The reliability of the experimental method was verified by simultaneously performing the Coulomb excitation experiment of 181Ta.

Photoinduced charge-transfer electronic excitation of tetracyanoethylene/tetramethylethylene complex in dichloromethane

NASA Astrophysics Data System (ADS)

Xu, Long-Kun; Bi, Ting-Jun; Ming, Mei-Jun; Wang, Jing-Bo; Li, Xiang-Yuan

2017-07-01

Based on the previous work on nonequilibrium solvation model by the authors, Intermolecular charge-transfer electronic excitation of tetracyanoethylene (TCE)/tetramethylethylene (TME) π -stacked complex in dichloromethane (DCM) has been investigated. For weak interaction correction, dispersion corrected functional DFT-D3 is adopted for geometry optimization. In order to identify the excitation metric, dipole moment components of each Cartesian direction, atomic charge, charge separation and Δr index are analyzed for TCE/TME complex. Calculation shows that the calculated excitation energy is dependent on the functional choice, when conjuncted with suitable time-dependent density functional, the modified nonequilibrium expression gives satisfied results for intermolecular charge-transfer electronic excitation.

Evidence for concerted ring opening and C-Br bond breaking in UV-excited bromocyclopropane.

PubMed

Pandit, Shubhrangshu; Preston, Thomas J; King, Simon J; Vallance, Claire; Orr-Ewing, Andrew J

2016-06-28

Photodissociation of gaseous bromocyclopropane via its A-band continuum has been studied at excitation wavelengths ranging from 230 nm to 267 nm. Velocity-map images of ground-state bromine atoms (Br), spin-orbit excited bromine atoms (Br(∗)), and C3H5 hydrocarbon radicals reveal the kinetic energies of these various photofragments. Both Br and Br(∗) atoms are predominantly generated via repulsive excited electronic states in a prompt photodissociation process in which the hydrocarbon co-fragment is a cyclopropyl radical. However, the images obtained at the mass of the hydrocarbon radical fragment identify a channel with total kinetic energy greater than that deduced from the Br and Br(∗) images, and with a kinetic energy distribution that exceeds the energetic limit for Br + cyclopropyl radical products. The velocity-map images of these C3H5 fragments have lower angular anisotropies than measured for Br and Br(∗), indicating molecular restructuring during dissociation. The high kinetic energy C3H5 signals are assigned to allyl radicals generated by a minor photochemical pathway which involves concerted C-Br bond dissociation and cyclopropyl ring-opening following single ultraviolet (UV)-photon absorption. Slow photofragments also contribute to the velocity map images obtained at the C3H5 radical mass, but the corresponding slow Br atoms are not observed. These features in the images are attributed to C3H5 (+) from the photodissociation of the C3H5Br(+) molecular cation following two-photon ionization of the parent compound. This assignment is confirmed by 118-nm vacuum ultraviolet ionization studies that prepare the molecular cation in its ground electronic state prior to UV photodissociation.

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.

Kinetic-energy release distributions of fragment anions from collisions of potassium atoms with D-Ribose and tetrahydrofuran*

NASA Astrophysics Data System (ADS)

Rebelo, André; Cunha, Tiago; Mendes, Mónica; da Silva, Filipe Ferreira; García, Gustavo; Limão-Vieira, Paulo

2016-06-01

Kinetic-energy release distributions have been obtained from the width and shapes of the time-of-flight (TOF) negative ion mass peaks formed in collisions of fast potassium atoms with D-Ribose (DR) and tetrahydrofuran (THF) molecules. Recent dissociative ion-pair formation experiments yielding anion formation have shown that the dominant fragment from D-Ribose is OH- [D. Almeida, F. Ferreira da Silva, G. García, P. Limão-Vieira, J. Chem. Phys. 139, 114304 (2013)] whereas in the case of THF is O- [D. Almeida, F. Ferreira da Silva, S. Eden, G. García, P. Limão-Vieira, J. Phys. Chem. A 118, 690 (2014)]. The results for DR and THF show an energy distribution profile reminiscent of statistical degradation via vibrational excitation and partly due to direct transformation of the excess energy in translational energy.

A Bibliography of Basic Books on Atomic Energy. Update.

ERIC Educational Resources Information Center

Atomic Energy Commission, Washington, DC. Office of Information Services.

This booklet, part of the United States Atomic Energy Commission's series of information booklets, lists selected commerically published books for the general public on atomic energy and closely related subjects. It includes annotated bibliographies for children (grade level indicated) and adults. The books are arranged by subject, alphabetized by…

Approach to thermal equilibrium in atomic collisions.

PubMed

Zhang, P; Kharchenko, V; Dalgarno, A; Matsumi, Y; Nakayama, T; Takahashi, K

2008-03-14

The energy relaxation of fast atoms moving in a thermal bath gas is explored experimentally and theoretically. Two time scales characterize the equilibration, one a short time, in which the isotropic energy distribution profile relaxes to a Maxwellian shape at some intermediate effective temperature, and the second, a longer time in which the relaxation preserves a Maxwellian distribution and its effective temperature decreases continuously to the bath gas temperature. The formation and preservation of a Maxwellian distribution does not depend on the projectile to bath gas atom mass ratio. This two-stage behavior arises due to the dominance of small angle scattering and small energy transfer in the collisions of neutral particles. Measurements of the evolving Doppler profiles of emission from excited initially energetic nitrogen atoms traversing bath gases of helium and argon confirm the theoretical predictions.

Estimating Atomic Contributions to Hydration and Binding Using Free Energy Perturbation.

PubMed

Irwin, Benedict W J; Huggins, David J

2018-06-12

We present a general method called atom-wise free energy perturbation (AFEP), which extends a conventional molecular dynamics free energy perturbation (FEP) simulation to give the contribution to a free energy change from each atom. AFEP is derived from an expansion of the Zwanzig equation used in the exponential averaging method by defining that the system total energy can be partitioned into contributions from each atom. A partitioning method is assumed and used to group terms in the expansion to correspond to individual atoms. AFEP is applied to six example free energy changes to demonstrate the method. Firstly, the hydration free energies of methane, methanol, methylamine, methanethiol, and caffeine in water. AFEP highlights the atoms in the molecules that interact favorably or unfavorably with water. Finally AFEP is applied to the binding free energy of human immunodeficiency virus type 1 protease to lopinavir, and AFEP reveals the contribution of each atom to the binding free energy, indicating candidate areas of the molecule to improve to produce a more strongly binding inhibitor. FEP gives a single value for the free energy change and is already a very useful method. AFEP gives a free energy change for each "part" of the system being simulated, where part can mean individual atoms, chemical groups, amino acids, or larger partitions depending on what the user is trying to measure. This method should have various applications in molecular dynamics studies of physical, chemical, or biochemical phenomena, specifically in the field of computational drug discovery.

Will a Decaying Atom Feel a Friction Force?

PubMed

Sonnleitner, Matthias; Trautmann, Nils; Barnett, Stephen M

2017-02-03

We show how a simple calculation leads to the surprising result that an excited two-level atom moving through a vacuum sees a tiny friction force of first order in v/c. At first sight this seems to be in obvious contradiction to other calculations showing that the interaction with the vacuum does not change the velocity of an atom. It is even more surprising that this change in the atom's momentum turns out to be a necessary result of energy and momentum conservation in special relativity.

Forbidden 2P–nP and 2P–nF transitions in the energy spectrum of ultracold Rydberg lithium-7 atoms

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zelener, B. B., E-mail: bobozel@mail.ru; Saakyan, S. A.; Sautenkov, V. A.

2016-04-15

Forbidden 2P–nP and 2P–nF transitions in the ranges of the principal quantum number n = 42–114 and n = 38–48 have been detected in the optical spectra of ultracold highly excited lithium-7 atoms. The presence of forbidden transitions is due to induced external electric fields. The quantum defects and ionization energy obtained in various experiments and predicted theoretically have been discussed.

Attenuation of Scattered Thermal Energy Atomic Oxygen

NASA Technical Reports Server (NTRS)

Banks, Bruce a.; Seroka, Katelyn T.; McPhate, Jason B.; Miller, Sharon K.

2011-01-01

The attenuation of scattered thermal energy atomic oxygen is relevant to the potential damage that can occur within a spacecraft which sweeps through atomic oxygen in low Earth orbit (LEO). Although there can be significant oxidation and resulting degradation of polymers and some metals on the external surfaces of spacecraft, there are often openings on a spacecraft such as telescope apertures, vents, and microwave cavities that can allow atomic oxygen to enter and scatter internally to the spacecraft. Atomic oxygen that enters a spacecraft can thermally accommodate and scatter to ultimately react or recombine on surfaces. The atomic oxygen that does enter a spacecraft can be scavenged by use of high erosion yield polymers to reduce its reaction on critical surfaces and materials. Polyoxymethylene and polyethylene can be used as effective atomic oxygen scavenging polymers.

QED theory of multiphoton transitions in atoms and ions

NASA Astrophysics Data System (ADS)

Zalialiutdinov, Timur A.; Solovyev, Dmitry A.; Labzowsky, Leonti N.; Plunien, Günter

2018-03-01

This review surveys the quantum theory of electromagnetic radiation for atomic systems. In particular, a review of current theoretical studies of multiphoton processes in one and two-electron atoms and highly charged ions is provided. Grounded on the quantum electrodynamics description the multiphoton transitions in presence of cascades, spin-statistic behaviour of equivalent photons and influence of external electric fields on multiphoton in atoms and anti-atoms are discussed. Finally, the nonresonant corrections which define the validity of the concept of the excited state energy levels are introduced.

Structures and Binding Energies of the Naphthalene Dimer in Its Ground and Excited States.

PubMed

Dubinets, N O; Safonov, A A; Bagaturyants, A A

2016-05-05

Possible structures of the naphthalene dimer corresponding to local energy minima in the ground and excited (excimer) electronic states are comprehensively investigated using DFT-D and TDDFT-D methods with a special accent on the excimer structures. The corresponding binding and electronic transition energies are calculated, and the nature of the electronic states in different structures is analyzed. Several parallel (stacked) and T-shaped structures were found in both the ground and excited (excimer) states in a rather narrow energy range. The T-shaped structure with the lowest energy in the excited state exhibits a marked charge transfer from the upright molecule to the base one.

Low-energy Coulomb excitation of neutron-rich zinc isotopes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Walle, J. van de; ISOLDE, CERN, Geneva; Aksouh, F.

2009-01-15

At the radioactive ion beam facility REX-ISOLDE, neutron-rich zinc isotopes were investigated using low-energy Coulomb excitation. These experiments have resulted in B(E2,2{sub 1}{sup +}{yields}0{sub 1}{sup +}) values in {sup 74-80}Zn, B(E2,4{sub 1}{sup +}{yields}2{sub 1}{sup +}) values in {sup 74,76}Zn and the determination of the energy of the first excited 2{sub 1}{sup +} states in {sup 78,80}Zn. The zinc isotopes were produced by high-energy proton- (A=74,76,80) and neutron- (A=78) induced fission of {sup 238}U, combined with selective laser ionization and mass separation. The isobaric beam was postaccelerated by the REX linear accelerator and Coulomb excitation was induced on a thin secondarymore » target, which was surrounded by the MINIBALL germanium detector array. In this work, it is shown how the selective laser ionization can be used to deal with the considerable isobaric beam contamination and how a reliable normalization of the experiment can be achieved. The results for zinc isotopes and the N=50 isotones are compared to collective model predictions and state-of-the-art large-scale shell-model calculations, including a recent empirical residual interaction constructed to describe the present experimental data up to 2004 in this region of the nuclear chart.« less

Nonlinear dynamic analysis of cantilevered piezoelectric energy harvesters under simultaneous parametric and external excitations

NASA Astrophysics Data System (ADS)

Fang, Fei; Xia, Guanghui; Wang, Jianguo

2018-02-01

The nonlinear dynamics of cantilevered piezoelectric beams is investigated under simultaneous parametric and external excitations. The beam is composed of a substrate and two piezoelectric layers and assumed as an Euler-Bernoulli model with inextensible deformation. A nonlinear distributed parameter model of cantilevered piezoelectric energy harvesters is proposed using the generalized Hamilton's principle. The proposed model includes geometric and inertia nonlinearity, but neglects the material nonlinearity. Using the Galerkin decomposition method and harmonic balance method, analytical expressions of the frequency-response curves are presented when the first bending mode of the beam plays a dominant role. Using these expressions, we investigate the effects of the damping, load resistance, electromechanical coupling, and excitation amplitude on the frequency-response curves. We also study the difference between the nonlinear lumped-parameter and distributed-parameter model for predicting the performance of the energy harvesting system. Only in the case of parametric excitation, we demonstrate that the energy harvesting system has an initiation excitation threshold below which no energy can be harvested. We also illustrate that the damping and load resistance affect the initiation excitation threshold.

Nonlinear dynamic analysis of cantilevered piezoelectric energy harvesters under simultaneous parametric and external excitations

NASA Astrophysics Data System (ADS)

Fang, Fei; Xia, Guanghui; Wang, Jianguo

2018-06-01

The nonlinear dynamics of cantilevered piezoelectric beams is investigated under simultaneous parametric and external excitations. The beam is composed of a substrate and two piezoelectric layers and assumed as an Euler-Bernoulli model with inextensible deformation. A nonlinear distributed parameter model of cantilevered piezoelectric energy harvesters is proposed using the generalized Hamilton's principle. The proposed model includes geometric and inertia nonlinearity, but neglects the material nonlinearity. Using the Galerkin decomposition method and harmonic balance method, analytical expressions of the frequency-response curves are presented when the first bending mode of the beam plays a dominant role. Using these expressions, we investigate the effects of the damping, load resistance, electromechanical coupling, and excitation amplitude on the frequency-response curves. We also study the difference between the nonlinear lumped-parameter and distributed-parameter model for predicting the performance of the energy harvesting system. Only in the case of parametric excitation, we demonstrate that the energy harvesting system has an initiation excitation threshold below which no energy can be harvested. We also illustrate that the damping and load resistance affect the initiation excitation threshold.

Probing local bias-induced transitions using photothermal excitation contact resonance atomic force microscopy and voltage spectroscopy

DOE PAGES

Li, Qian; Jesse, Stephen; Tselev, Alexander; ...

2015-01-05

In this paper, nanomechanical properties are closely related to the states of matter, including chemical composition, crystal structure, mesoscopic domain configuration, etc. Investigation of these properties at the nanoscale requires not only static imaging methods, e.g., contact resonance atomic force microscopy (CR-AFM), but also spectroscopic methods capable of revealing their dependence on various external stimuli. Here we demonstrate the voltage spectroscopy of CR-AFM, which was realized by combining photothermal excitation (as opposed to the conventional piezoacoustic excitation method) with the band excitation technique. We applied this spectroscopy to explore local bias-induced phenomena ranging from purely physical to surface electromechanical andmore » electrochemical processes. Our measurements show that the changes in the surface properties associated with these bias-induced transitions can be accurately assessed in a fast and dynamic manner, using resonance frequency as a signature. Finally, with many of the advantages offered by photothermal excitation, contact resonance voltage spectroscopy not only is expected to find applications in a broader field of nanoscience but also will provide a basis for future development of other nanoscale elastic spectroscopies.« less

Radiation pressure excitation of Low Temperature Atomic Force & Magnetic Force Microscope (LT-AFM/MFM) for Imaging

NASA Astrophysics Data System (ADS)

Karci, Ozgur; Celik, Umit; Oral, Ahmet; NanoMagnetics Instruments Ltd. Team; Middle East Tech Univ Team

2015-03-01

We describe a novel method for excitation of Atomic Force Microscope (AFM) cantilevers by means of radiation pressure for imaging in an AFM for the first time. Piezo excitation is the most common method for cantilever excitation, but it may cause spurious resonance peaks. A fiber optic interferometer with 1310 nm laser was used both to measure the deflection of cantilever and apply a force to the cantilever in a LT-AFM/MFM from NanoMagnetics Instruments. The laser power was modulated at the cantilever`s resonance frequency by a digital Phase Lock Loop (PLL). The force exerted by the radiation pressure on a perfectly reflecting surface by a laser beam of power P is F = 2P/c. We typically modulate the laser beam by ~ 800 μW and obtain 10nm oscillation amplitude with Q ~ 8,000 at 2.5x10-4 mbar. The cantilever's stiffness can be accurately calibrated by using the radiation pressure. We have demonstrated performance of the radiation pressure excitation in AFM/MFM by imaging a hard disk sample between 4-300K and Abrikosov vortex lattice in BSCCO single crystal at 4K to for the first time.

Two-Centre Convergent Close-Coupling Approach to Ion-Atom Collisions: Current Progress

NASA Astrophysics Data System (ADS)

Kadyrov, Alisher; Abdurakhmanov, Ilkhom; Bailey, Jackson; Bray, Igor

2016-09-01

There are two versions of the convergent close-coupling (CCC) approach to ion-atom collisions: quantum-mechanical (QM-CCC) and semi-classical (SC-CCC). Recently, both implementations have been extended to include electron-transfer channels. The SC-CCC approach has been applied to study the excitation and the electron-capture processes in proton-hydrogen collisions. The integral alignment parameter A20 for polarization of Lyman- α emission and the cross sections for excitation and electron-capture into the lowest excited states have been calculated for a wide range of the proton impact energies. It has been established that for convergence of the results a very wide range of impact parameters (typically, 0-50 a.u.) is required due to extremely long tails of transition probabilities for transitions into the 2 p states at high energies. The QM-CCC approach allowed to obtain an accurate solution of proton-hydrogen scattering problem including all underlying processes, namely, direct scattering and ionisation, and electron capture into bound and continuum states of the projectile. In this presentation we give a general overview of current progress in applications of the two-centre CCC approach to ion-atom and atom-atom collisions. The work is supported by the Australian Research Council.

Correlated wave functions for three-particle systems with Coulomb interaction - The muonic helium atom

NASA Technical Reports Server (NTRS)

Huang, K.-N.

1977-01-01

A computational procedure for calculating correlated wave functions is proposed for three-particle systems interacting through Coulomb forces. Calculations are carried out for the muonic helium atom. Variational wave functions which explicitly contain interparticle coordinates are presented for the ground and excited states. General Hylleraas-type trial functions are used as the basis for the correlated wave functions. Excited-state energies of the muonic helium atom computed from 1- and 35-term wave functions are listed for four states.

The Harnessed Atom: Nuclear Energy & Electricity.

ERIC Educational Resources Information Center

Department of Energy, Washington, DC. Nuclear Energy Office.

This document is part of a nuclear energy curriculum designed for grades six through eight. The complete kit includes a written text, review exercises, activities for the students, and a teachers guide. The 19 lessons in the curriculum are divided into four units including: (1) "Energy and Electricity"; (2) "Understanding Atoms and Radiation"; (3)…

Even-parity resonances with synchrotron radiation from Laser Excited Lithium at 1s^22p State

NASA Astrophysics Data System (ADS)

Huang, Ming-Tie; Wehlitz, Ralf

2010-03-01

Correlated many-body dynamics is still one of the unsolved fundamental problems in physics. Such correlation effects can be most clearly studied in processes involving single atoms for their simplicity.Lithium, being the simplest open shell atom, has been under a lot of study. Most of the studies focused on ground state lithium. However, only odd parity resonances can be populated through single photon (synchrotron radiation) absorption from ground state lithium (1s^22s). Lithium atoms, after being laser excited to the 1s^22p state, allow the study of even parity resonances. We have measured some of the even parity resonances of lithium for resonant energies below 64 eV. A single-mode diode laser is used to excite lithium from 1s^22s ground state to 1s^22p (^2P3/2) state. Photoions resulting from the interaction between the excited lithium and synchrotron radiation were analyzed and collected by an ion time-of-flight (TOF) spectrometer with a Z- stack channel plate detector. The Li^+ ion yield was recorded while scanning the undulator along with the monochromator. The energy scans have been analyzed regarding resonance energies and parameters of the Fano profiles. Our results for the observed resonances will be presented.

Relaxation times measurement in single and multiply excited xenon clusters

NASA Astrophysics Data System (ADS)

Serdobintsev, P. Yu.; Melnikov, A. S.; Pastor, A. A.; Timofeev, N. A.; Khodorkovskiy, M. A.

2018-05-01

Direct measurement of the rates of nonradiative relaxation processes in electronically excited xenon clusters was carried out. The clusters were created in a pulsed supersonic beam and two-photon excited by femtosecond laser pulses with a wavelength of 263 nm. The measurements were performed using the pump-probe method and electron spectroscopy. It is shown that relaxation of light clusters XeN (N < 15) predominantly occurs by desorption of excited xenon atoms with a characteristic time constant of 3 ps. Heavier electronically excited clusters (N > 10) vibrationally relax to the lowest electronically excited state at a rate of about 0.075 eV/ps. Multiply excited clusters are deactivated via energy exchange between excited centers with the ionization of one of them. The production of electrons in this process occurs with a delay of ˜4 ps from the pump pulse, and the process is completed in 10 ps.

Kinetics of highly vibrationally excited O2(X) molecules in inductively-coupled oxygen plasmas

NASA Astrophysics Data System (ADS)

Annušová, Adriana; Marinov, Daniil; Booth, Jean-Paul; Sirse, Nishant; Lino da Silva, Mário; Lopez, Bruno; Guerra, Vasco

2018-04-01

The high degree of vibrational excitation of O2 ground state molecules recently observed in inductively coupled plasma discharges is investigated experimentally in more detail and interpreted using a detailed self-consistent 0D global kinetic model for oxygen plasmas. Additional experimental results are presented and used to validate the model. The vibrational kinetics considers vibrational levels up to v = 41 and accounts for electron impact excitation and de-excitation (e-V), vibration-to-translation relaxation (V-T) in collisions with O2 molecules and O atoms, vibration-to-vibration energy exchanges (V-V), excitation of electronically excited states, dissociative electron attachment, and electron impact dissociation. Measurements were performed at pressures of 10–80 mTorr (1.33 and 10.67 Pa) and radio frequency (13.56 MHz) powers up to 500 W. The simulation results are compared with the absolute densities in each O2 vibrational level obtained by high sensitivity absorption spectroscopy measurements of the Schumann–Runge bands for O2(X, v = 4–18), O(3 P) atom density measurements by two-photon absorption laser induced fluorescence (TALIF) calibrated against Xe, and laser photodetachment measurements of the O‑ negative ions. The highly excited O2(X, v) distribution exhibits a shape similar to a Treanor-Gordiets distribution, but its origin lies in electron impact e-V collisions and not in V-V up-pumping, in contrast to what happens in all other molecular gases known to date. The relaxation of vibrational quanta is mainly due to V-T energy-transfer collisions with O atoms and to electron impact dissociation of vibrationally excited molecules, e+O2(X, v)→O(3P)+O(3P).

Multipolar electrostatics for proteins: atom-atom electrostatic energies in crambin.

PubMed

Yuan, Yongna; Mills, Matthew J L; Popelier, Paul L A

2014-02-15

Accurate electrostatics necessitates the use of multipole moments centered on nuclei or extra point charges centered away from the nuclei. Here, we follow the former alternative and investigate the convergence behavior of atom-atom electrostatic interactions in the pilot protein crambin. Amino acids are cut out from a Protein Data Bank structure of crambin, as single amino acids, di, or tripeptides, and are then capped with a peptide bond at each side. The atoms in the amino acids are defined through Quantum Chemical Topology (QCT) as finite volume electron density fragments. Atom-atom electrostatic energies are computed by means of a multipole expansion with regular spherical harmonics, up to a total interaction rank of L = ℓA+ ℓB + 1 = 10. The minimum internuclear distance in the convergent region of all the 15 possible types of atom-atom interactions in crambin that were calculated based on single amino acids are close to the values calculated from di and tripeptides. Values obtained at B3LYP/aug-cc-pVTZ and MP2/aug-cc-pVTZ levels are only slightly larger than those calculated at HF/6-31G(d,p) level. This convergence behavior is transferable to the well-known amyloid beta polypeptide Aβ1-42. Moreover, for a selected central atom, the influence of its neighbors on its multipole moments is investigated, and how far away this influence can be ignored is also determined. Finally, the convergence behavior of AMBER becomes closer to that of QCT with increasing internuclear distance. Copyright © 2013 Wiley Periodicals, Inc.

Plasmon assisted control of photo-induced excitation energy transfer in a molecular chain

NASA Astrophysics Data System (ADS)

Wang, Luxia; May, Volkhard

2017-08-01

The strong and ultrafast laser pulse excitation of a molecular chain in close vicinity to a spherical metal nano-particle (MNP) is studied theoretically. Due to local-field enhancement around the MNP, pronounced excited-state formation has to be expected for the part of the chain which is in proximity to the MNP. Here, the description of this phenomenon will be based on a uniform quantum theory of the MNP-molecule system. It accounts for local-field effects due to direct consideration of the strong excitation energy transfer coupling between the MNP and the various molecules. The molecule-MNP distances are chosen in such a way as to achieve a correct description of the MNP via dipole-plasmon excitations. Short plasmon life-times are incorporated in the framework of a density matrix approach. By extending earlier work the present description allows for multi-exciton formation and multiple dipole-plasmon excitation. The region of less intense and not-too-short optical excitation is identified as being best suited for excitation energy localization in the chain.

Dissociative Excitation of Adenine by Electron Impact

NASA Astrophysics Data System (ADS)

McConkey, J. William; Trocchi, Joshuah; Dech, Jeffery; Kedzierski, Wladek

2017-04-01

Dissociative excitation of adenine (C6H5NH2) into excited atomic fragments has been studied in the electron impact energy range from threshold to 300 eV. A crossed beam system coupled to a vacuum ultraviolet (VUV) monochromator is used to study emissions in the wavelength range from 110 to 200 nm. The beam of adenine vapor from a stainless steel oven is crossed at right angles by the electron beam and the resultant UV radiation is detected in a mutually orthogonal direction. The strongest feature in the spectrum is H Lyman- α. Financial support from NSERC and CFI, Canada, is gratefully acknowledged.

Study of np{sup 2}P{sub 1/2,3/2} Rydberg series of AlI by the method of laser stepwise excitation and ionization by electric field

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kasimov, A.K.; Tursunov, A.T.; Tukhlibaev, O.

Frequencies of the 4s{sup 2}S{sub 1/2}-np{sup 2}P{sub 1/2, 3/2} transitions are measured and the energies of high-lying P states, as well as the ionization energy of aluminum atoms, are determined by the method of two-step laser excitation and ionization of excited atoms of AlI by an electric field. 4 refs., 3 figs., 1 tab.

Translations from the Soviet Journal of Atomic Energy

DTIC Science & Technology

1962-02-15

constructing a new communist society. Atomic energy, i4n its role of a new and powerful source of highly con •entrated energy, can effect a con- siderable...problem have provided sufficient evidence of the perni- cious effects of radioactive contamination on humanbeings and require the development of special...be necessary to effect a considerable decrease in the cost of electrical power pro- duced at atomic electric power, stations. One of the most

Effects of multiple pathways on excited-state energy flow in self-assembled wheel-and-spoke light-harvesting architectures.

PubMed

Song, Hee-eun; Kirmaier, Christine; Schwartz, Jennifer K; Hindin, Eve; Yu, Lianhe; Bocian, David F; Lindsey, Jonathan S; Holten, Dewey

2006-10-05

Static and time-resolved optical measurements are reported for three cyclic hexameric porphyrin arrays and their self-assembled complexes with guest chromophores. The hexameric hosts contain zinc porphyrins and 0, 1, or 2 free base (Fb) porphyrins (denoted Zn(6), Zn(5)Fb, or Zn(4)Fb(2), respectively). The guest is a core-modified (O replacing one of the four N atoms) dipyridyl-substituted Fb porphyrin (DPFbO) that coordinates to zinc porphyrins of a host via pyridyl-zinc dative bonding. Each architecture is designed to have a gradient of excited-state energies for excitation funneling among the weakly coupled constituents of the host to the guest. Energy transfer to the lowest-energy chromophore(s) (coordinated zinc porphyrins or Fb porphyrins) within a hexameric host occurs primarily via a through-bond (TB) mechanism, is rapid ( approximately 40 ps), and is essentially quantitative (>or=98%). Energy transfer from a pyridyl-coordinated zinc porphyrin of the host to the guest in the Zn(6)*DPFbO complex has a yield of approximately 75%, a rate constant of approximately (0.7 ns)(-1), and significant Förster through-space (TS) character. In the case of Zn(5)Fb*DPFbO, which has an additional TS route via the Fb porphyrin with a rate constant of approximately (20 ns)(-1), the yield of energy transfer to the guest is somewhat lower ( approximately 50%) than that for Zn(6)*DPFbO. Complex Zn(4)Fb(2)*DPFbO has an identical TS pathway via the Fb porphyrin plus an additional TS pathway involving the second Fb porphyrin (closer to the guest) with a rate constant of approximately (0.5 ns)(-1). This complex exhibits an energy-transfer yield to the guest that is significantly enhanced over that for Zn(5)Fb*DPFbO and comparable to that for Zn(6)*DPFbO. Collectively, the results for the various arrays suggest designs for similar host-guest complexes that are expected to exhibit much more efficient light harvesting and excitation trapping at the central guest chromophore.

Rotational excitation of symmetric top molecules by collisions with atoms: Close coupling, coupled states, and effective potential calculations for NH3-He

NASA Technical Reports Server (NTRS)

Green, S.

1976-01-01

The formalism for describing rotational excitation in collisions between symmetric top rigid rotors and spherical atoms is presented both within the accurate quantum close coupling framework and also the coupled states approximation of McGuire and Kouri and the effective potential approximation of Rabitz. Calculations are reported for thermal energy NH3-He collisions, treating NH3 as a rigid rotor and employing a uniform electron gas (Gordon-Kim) approximation for the intermolecular potential. Coupled states are found to be in nearly quantitative agreement with close coupling results while the effective potential method is found to be at least qualitatively correct. Modifications necessary to treat the inversion motion in NH3 are discussed.

Maximizing direct current power delivery from bistable vibration energy harvesting beams subjected to realistic base excitations

NASA Astrophysics Data System (ADS)

Dai, Quanqi; Harne, Ryan L.

2017-04-01

Effective development of vibration energy harvesters is required to convert ambient kinetic energy into useful electrical energy as power supply for sensors, for example in structural health monitoring applications. Energy harvesting structures exhibiting bistable nonlinearities have previously been shown to generate large alternating current (AC) power when excited so as to undergo snap-through responses between stable equilibria. Yet, most microelectronics in sensors require rectified voltages and hence direct current (DC) power. While researchers have studied DC power generation from bistable energy harvesters subjected to harmonic excitations, there remain important questions as to the promise of such harvester platforms when the excitations are more realistic and include both harmonic and random components. To close this knowledge gap, this research computationally and experimentally studies the DC power delivery from bistable energy harvesters subjected to such realistic excitation combinations as those found in practice. Based on the results, it is found that the ability for bistable energy harvesters to generate peak DC power is significantly reduced by introducing sufficient amount of stochastic excitations into an otherwise harmonic input. On the other hand, the elimination of a low amplitude, coexistent response regime by way of the additive noise promotes power delivery if the device was not originally excited to snap-through. The outcomes of this research indicate the necessity for comprehensive studies about the sensitivities of DC power generation from bistable energy harvester to practical excitation scenarios prior to their optimal deployment in applications.

Atomic Data for the CHIANTI Database

NASA Technical Reports Server (NTRS)

Bhatia, Anand K.; Landi, E.

2012-01-01

The CHIANTI spectral code consists of an atomic database and a suite of computer programs to calculate the optically thin spectrum of astrophysical objects and to carry out spectroscopic plasma diagnostics. The database includes atomic energy levels, wavelengths, radiative transition rates, collisional excitation, ionization and recombination rate coefficients, as well as data to calculate free-free, free-bound and two-photon continuum emission. In recent years, we have been pursuing a program to calculate atomic data for ions whose lines have been observed in astrophysical spectra but have been neglected in the literature, and to provide CHIANTI with all the data necessary to predict line intensities. There are two types of such ions: those for which calculations are available for low-energy configurations but not for high-energy configurations (i.e., C-like, N-like, O-like systems), and ions that have never or only seldom been studied. This poster will summarize the current status of this project and indicate the future activities .

Energy cascades, excited state dynamics, and photochemistry in cob(III)alamins and ferric porphyrins.

PubMed

Rury, Aaron S; Wiley, Theodore E; Sension, Roseanne J

2015-03-17

Porphyrins and the related chlorins and corrins contain a cyclic tetrapyrrole with the ability to coordinate an active metal center and to perform a variety of functions exploiting the oxidation state, reactivity, and axial ligation of the metal center. These compounds are used in optically activated applications ranging from light harvesting and energy conversion to medical therapeutics and photodynamic therapy to molecular electronics, spintronics, optoelectronic thin films, and optomagnetics. Cobalt containing corrin rings extend the range of applications through photolytic cleavage of a unique axial carbon-cobalt bond, permitting spatiotemporal control of drug delivery. The photochemistry and photophysics of cyclic tetrapyrroles are controlled by electronic relaxation dynamics including internal conversion and intersystem crossing. Typically the electronic excitation cascades through ring centered ππ* states, ligand to metal charge transfer (LMCT) states, metal to ligand charge transfer (MLCT) states, and metal centered states. Ultrafast transient absorption spectroscopy provides a powerful tool for the investigation of the electronic state dynamics in metal containing tetrapyrroles. The UV-visible spectrum is sensitive to the oxidation state, electronic configuration, spin state, and axial ligation of the central metal atom. Ultrashort broadband white light probes spanning the range from 270 to 800 nm, combined with tunable excitation pulses, permit the detailed unravelling of the time scales involved in the electronic energy cascade. State-of-the-art theoretical calculations provide additional insight required for precise assignment of the states. In this Account, we focus on recent ultrafast transient absorption studies of ferric porphyrins and corrin containing cob(III)alamins elucidating the electronic states responsible for ultrafast energy cascades, excited state dynamics, and the resulting photoreactivity or photostability of these compounds. Iron

Dynamics of atom-atom correlations in the Fermi problem

NASA Astrophysics Data System (ADS)

Borrelli, Massimo; Sabín, Carlos; Adesso, Gerardo; Plastina, Francesco; Maniscalco, Sabrina

2012-10-01

We present a detailed perturbative study of the dynamics of several types of atom-atom correlations in the famous Fermi problem. This is an archetypal model to study micro-causality in the quantum domain, where two atoms, one initially excited and the other prepared in its ground state, interact with the vacuum electromagnetic field. The excitation can be transferred to the second atom via a flying photon, and various kinds of quantum correlations between the two are generated during this process. Among these, prominent examples are given by entanglement, quantum discord and non-local correlations. The aim of this paper is to analyze the role of the light cone in the emergence of such correlations.

Coherent transport and energy flow patterns in photosynthesis under incoherent excitation.

PubMed

Pelzer, Kenley M; Can, Tankut; Gray, Stephen K; Morr, Dirk K; Engel, Gregory S

2014-03-13

Long-lived coherences have been observed in photosynthetic complexes after laser excitation, inspiring new theories regarding the extreme quantum efficiency of photosynthetic energy transfer. Whether coherent (ballistic) transport occurs in nature and whether it improves photosynthetic efficiency remain topics of debate. Here, we use a nonequilibrium Green's function analysis to model exciton transport after excitation from an incoherent source (as opposed to coherent laser excitation). We find that even with an incoherent source, the rate of environmental dephasing strongly affects exciton transport efficiency, suggesting that the relationship between dephasing and efficiency is not an artifact of coherent excitation. The Green's function analysis provides a clear view of both the pattern of excitonic fluxes among chromophores and the multidirectionality of energy transfer that is a feature of coherent transport. We see that even in the presence of an incoherent source, transport occurs by qualitatively different mechanisms as dephasing increases. Our approach can be generalized to complex synthetic systems and may provide a new tool for optimizing synthetic light harvesting materials.

Electron-impact coherence parameters for 41 P 1 excitation of zinc

NASA Astrophysics Data System (ADS)

Piwiński, Mariusz; Kłosowski, Łukasz; Chwirot, Stanisław; Fursa, Dmitry V.; Bray, Igor; Das, Tapasi; Srivastava, Rajesh

2018-04-01

We present electron-impact coherence parameters (EICP) for electron-impact excitation of 41 P 1 state of zinc atoms for collision energies 40 eV and 60 eV. The experimental results are presented together with convergent close-coupling and relativistic distorted-wave approximation theoretical predictions. The results are compared and discussed with EICP data for collision energies 80 eV and 100 eV.

On the treatment of ℓ-changing proton-hydrogen Rydberg atom collisions

NASA Astrophysics Data System (ADS)

Vrinceanu, D.; Onofrio, R.; Sadeghpour, H. R.

2017-11-01

Energy-conserving, angular momentum changing collisions between protons and highly excited Rydberg hydrogen atoms are important for precise understanding of atomic recombination at the photon decoupling era and the elemental abundance after primordial nucleosynthesis. Early approaches to ℓ-changing collisions used perturbation theory only for dipole-allowed (Δℓ = ±1) transitions. An exact non-perturbative quantum mechanical treatment is possible, but it comes at a computational cost for highly excited Rydberg states. In this paper, we show how to obtain a semiclassical limit that is accurate and simple, and develop further physical insights afforded by the non-perturbative quantum mechanical treatment.

Following electron impact excitation of single (N, O, F, Ne, Na, Mg, Al, Si) atom L subshells ionization cross section calculations by using Lotz's equation

NASA Astrophysics Data System (ADS)

Aydinol, Mahmut

2017-02-01

L shell and L subshells ionization cross sections σL and σLi (i = 1, 2, 3) following electron impact on (N,O, F, Ne, Na, Mg, Al, Si) atoms calculated. By using Lotz' equation for nonrelativistic cases in Matlab σL and σLi cross section values obtained for ten electron impact(Eo) values in the range of ELiatom. Starting from Eo=ELi(each subshell ionization threshold energy), σL and σLi are increasing rapidly with Eo. For a fixed Eo value(≈3.ELi), while Z value increases from 7≤Z≤14 σL and σLi decrease. Results show that for smaller values of Eo(close to ELi), x-ray yields formation of Li(i=1,2,3) subshells decreases while competing other yields are increase. Results may help to understand similar findings which obtained from other electron impact excitation of L shell σL and subshells σLi studies for single atoms.

Energy dissipation unveils atomic displacement in the noncontact atomic force microscopy imaging of Si(111 )-(7 ×7 )

NASA Astrophysics Data System (ADS)

Arai, Toyoko; Inamura, Ryo; Kura, Daiki; Tomitori, Masahiko

2018-03-01

The kinetic energy of the oscillating cantilever of noncontact atomic force microscopy (nc-AFM) at room temperature was considerably dissipated over regions between a Si adatom and its neighboring rest atom for Si(111 )-(7 ×7 ) in close proximity to a Si tip on the cantilever. However, nc-AFM topographic images showed no atomic features over those regions, which were the hollow sites of the (7 ×7 ). This energy dissipation likely originated from displacement of Si adatoms with respect to the tip over the hollow sites, leading to a lateral shift of the adatoms toward the rest atom. This interaction led to hysteresis over each cantilever oscillation cycle; when the tip was retracted, the Si adatom likely returned to its original position. To confirm the atomic processes involved in the force interactions through Si dangling bonds, the Si(111 )-(7 ×7 ) surface was partly terminated with atomic hydrogen (H) and examined by nc-AFM. When the Si adatoms and/or the rest atoms were terminated with H, the hollow sites were not bright (less dissipation) in images of the energy dissipation channels by nc-AFM. The hollow sites acted as metastable sites for Si adatoms in surface diffusion and atom manipulation; thus, the dissipation energy which is saturated on the tip likely corresponds to the difference in the potential energy between the hollow site and the Si adatom site. In this study, we demonstrated the ability of dissipation channels of nc-AFM to enable visualization of the dynamics of atoms and molecules on surfaces, which cannot be revealed by nc-AFM topographic images alone.

Atom-by-atom assembly

NASA Astrophysics Data System (ADS)

Hla, Saw Wai

2014-05-01

Atomic manipulation using a scanning tunneling microscope (STM) tip enables the construction of quantum structures on an atom-by-atom basis, as well as the investigation of the electronic and dynamical properties of individual atoms on a one-atom-at-a-time basis. An STM is not only an instrument that is used to ‘see’ individual atoms by means of imaging, but is also a tool that is used to ‘touch’ and ‘take’ the atoms, or to ‘hear’ their movements. Therefore, the STM can be considered as the ‘eyes’, ‘hands’ and ‘ears’ of the scientists, connecting our macroscopic world to the exciting atomic world. In this article, various STM atom manipulation schemes and their example applications are described. The future directions of atomic level assembly on surfaces using scanning probe tips are also discussed.

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.

Existence of Hartree-Fock excited states for atoms and molecules

NASA Astrophysics Data System (ADS)

Lewin, Mathieu

2018-04-01

For neutral and positively charged atoms and molecules, we prove the existence of infinitely many Hartree-Fock critical points below the first energy threshold (that is, the lowest energy of the same system with one electron removed). This is the equivalent, in Hartree-Fock theory, of the famous Zhislin-Sigalov theorem which states the existence of infinitely many eigenvalues below the bottom of the essential spectrum of the N-particle linear Schrödinger operator. Our result improves a theorem of Lions in 1987 who already constructed infinitely many Hartree-Fock critical points, but with much higher energy. Our main contribution is the proof that the Hartree-Fock functional satisfies the Palais-Smale property below the first energy threshold. We then use minimax methods in the N-particle space, instead of working in the one-particle space.

Mapping the demise of collective motion in nuclei at high excitation energy

NASA Astrophysics Data System (ADS)

Santonocito, D.; Blumenfeld, Y.; Maiolino, C.; Agodi, C.; Alba, R.; Bellia, G.; Coniglione, R.; Del Zoppo, A.; Hongmei, F.; Migneco, E.; Piattelli, P.; Sapienza, P.; Auditore, L.; Cardella, G.; De Filippo, E.; La Guidara, E.; Monrozeau, C.; Papa, M.; Pirrone, S.; Rizzo, F.; Trifiró, A.; Trimarchi, M.; Huang, H. X.; Wieland, O.

2018-07-01

High energy gamma-rays from the 116Sn + 24Mg reaction at 23A MeV were measured using the MEDEA detector at LNS - INFN Catania. Combining this new data with previous measurements yields a detailed view of the quenching of the Giant Dipole Resonance as a function of excitation energy in nuclei of mass A in the range 120 ÷ 132. The transition towards the disappearance of the dipole strength, which occurs around 230 MeV excitation energy, appears to be remarkably sharp. Current phenomenological models give qualitative explanations for the quenching but cannot reproduce its detailed features.

Relativistic calculations of atomic properties

NASA Astrophysics Data System (ADS)

Kaur, Jasmeet; Sahoo, B. K.; Arora, Bindiya

2017-04-01

Singly charged ions are engaging candidates in many areas of Physics. They are especially important in astrophysics for evaluating the radiative properties of stellar objects, in optical frequency standards and for fundamental physics studies such as searches for permanent electric dipole moments and atomic parity violation. Interpretation of these experiments often requires a knowledge of their transition wavelengths and electric dipole amplitudes. In this work, we discuss the calculation of various properties of alkaline earth ions. The relativistic all-order SD method in which all single and double excitations of the Dirac-Fock wave function are included, is used to calculate these atomic properties. We use this method for evaluation of electric dipole matrix elements of alkaline earth ions. Combination of these matrix elements with experimental energies allow to obtain the polarizabilities of ground and excited states of ions. We discuss the applications of estimated polarizabiities as a function of imaginary frequencies in the calculations of long-range atom-ion interactions. We have also located the magic wavelengths for nS1 / 2 - nD3 / 2 , 5 / 2 transitions of alkaline earth ions. These calculated properties will be highly valuable to atomic and astrophysics community. UGC-BSR Grant No. F.7-273/2009/BSR.

Quantum oscillations of nitrogen atoms in uranium nitride

NASA Astrophysics Data System (ADS)

Aczel, A. A.; Granroth, G. E.; MacDougall, G. J.; Buyers, W. J. L.; Abernathy, D. L.; Samolyuk, G. D.; Stocks, G. M.; Nagler, S. E.

2012-10-01

The vibrational excitations of crystalline solids corresponding to acoustic or optic one-phonon modes appear as sharp features in measurements such as neutron spectroscopy. In contrast, many-phonon excitations generally produce a complicated, weak and featureless response. Here we present time-of-flight neutron scattering measurements for the binary solid uranium nitride, showing well-defined, equally spaced, high-energy vibrational modes in addition to the usual phonons. The spectrum is that of a single atom, isotropic quantum harmonic oscillator and characterizes independent motions of light nitrogen atoms, each found in an octahedral cage of heavy uranium atoms. This is an unexpected and beautiful experimental realization of one of the fundamental, exactly solvable problems in quantum mechanics. There are also practical implications, as the oscillator modes must be accounted for in the design of generation IV nuclear reactors that plan to use uranium nitride as a fuel.

Quantum oscillations of nitrogen atoms in uranium nitride.

PubMed

Aczel, A A; Granroth, G E; Macdougall, G J; Buyers, W J L; Abernathy, D L; Samolyuk, G D; Stocks, G M; Nagler, S E

2012-01-01

The vibrational excitations of crystalline solids corresponding to acoustic or optic one-phonon modes appear as sharp features in measurements such as neutron spectroscopy. In contrast, many-phonon excitations generally produce a complicated, weak and featureless response. Here we present time-of-flight neutron scattering measurements for the binary solid uranium nitride, showing well-defined, equally spaced, high-energy vibrational modes in addition to the usual phonons. The spectrum is that of a single atom, isotropic quantum harmonic oscillator and characterizes independent motions of light nitrogen atoms, each found in an octahedral cage of heavy uranium atoms. This is an unexpected and beautiful experimental realization of one of the fundamental, exactly solvable problems in quantum mechanics. There are also practical implications, as the oscillator modes must be accounted for in the design of generation IV nuclear reactors that plan to use uranium nitride as a fuel.

Understanding Atomic Structure: Is There a More Direct and Compelling Connection between Atomic Line Spectra and the Quantization of an Atom's Energy?

ERIC Educational Resources Information Center

Rittenhouse, Robert C.

2015-01-01

The "atoms first" philosophy, adopted by a growing number of General Chemistry textbook authors, places greater emphasis on atomic structure as a key to a deeper understanding of the field of chemistry. A pivotal concept needed to understand the behavior of atoms is the restriction of an atom's energy to specific allowed values. However,…

Excitation Anisotropy in Laser-Induced-Fluorescence Spectroscopy —High-Intensity, Broad-Line Excitation

NASA Astrophysics Data System (ADS)

Hirabayashi, Atsumu; Nambu, Yoshihiro; Fujimoto, Takashi

1986-10-01

The problem of excitation anisotropy in laser-induced-fluorescence spectroscopy (LIFS) was investigated for the intense excitation case under the broad-line condition. The depolarization coefficient for the fluorescence light was derived in the intense-excitation limit (linearly-polarized or unpolarized light excitation) and the results are presented in tables. In the region of intermediate intensity, between the weak and intense-excitation limits, the master equation was solved for a specific example of atomic transitions and its result is compared with experimental results.

Direct computation of general chemical energy differences: Application to ionization potentials, excitation, and bond energies.

PubMed

Beste, A; Harrison, R J; Yanai, T

2006-08-21

Chemists are mainly interested in energy differences. In contrast, most quantum chemical methods yield the total energy which is a large number compared to the difference and has therefore to be computed to a higher relative precision than would be necessary for the difference alone. Hence, it is desirable to compute energy differences directly, thereby avoiding the precision problem. Whenever it is possible to find a parameter which transforms smoothly from an initial to a final state, the energy difference can be obtained by integrating the energy derivative with respect to that parameter (cf. thermodynamic integration or adiabatic connection methods). If the dependence on the parameter is predominantly linear, accurate results can be obtained by single-point integration. In density functional theory and Hartree-Fock, we applied the formalism to ionization potentials, excitation energies, and chemical bond breaking. Example calculations for ionization potentials and excitation energies showed that accurate results could be obtained with a linear estimate. For breaking bonds, we introduce a nongeometrical parameter which gradually turns the interaction between two fragments of a molecule on. The interaction changes the potentials used to determine the orbitals as well as the constraint on the orbitals to be orthogonal.

Energy transport in weakly nonlinear wave systems with narrow frequency band excitation.

PubMed

Kartashova, Elena

2012-10-01

A novel discrete model (D model) is presented describing nonlinear wave interactions in systems with small and moderate nonlinearity under narrow frequency band excitation. It integrates in a single theoretical frame two mechanisms of energy transport between modes, namely, intermittency and energy cascade, and gives the conditions under which each regime will take place. Conditions for the formation of a cascade, cascade direction, conditions for cascade termination, etc., are given and depend strongly on the choice of excitation parameters. The energy spectra of a cascade may be computed, yielding discrete and continuous energy spectra. The model does not require statistical assumptions, as all effects are derived from the interaction of distinct modes. In the example given-surface water waves with dispersion function ω(2)=gk and small nonlinearity-the D model predicts asymmetrical growth of side-bands for Benjamin-Feir instability, while the transition from discrete to continuous energy spectrum, excitation parameters properly chosen, yields the saturated Phillips' power spectrum ~g(2)ω(-5). The D model can be applied to the experimental and theoretical study of numerous wave systems appearing in hydrodynamics, nonlinear optics, electrodynamics, plasma, convection theory, etc.

Variable energy, high flux, ground-state atomic oxygen source

NASA Technical Reports Server (NTRS)

Chutjian, Ara (Inventor); Orient, Otto J. (Inventor)

1987-01-01

A variable energy, high flux atomic oxygen source is described which is comprised of a means for producing a high density beam of molecules which will emit O(-) ions when bombarded with electrons; a means of producing a high current stream of electrons at a low energy level passing through the high density beam of molecules to produce a combined stream of electrons and O(-) ions; means for accelerating the combined stream to a desired energy level; means for producing an intense magnetic field to confine the electrons and O(-) ions; means for directing a multiple pass laser beam through the combined stream to strip off the excess electrons from a plurality of the O(-) ions to produce ground-state O atoms within the combined stream; electrostatic deflection means for deflecting the path of the O(-) ions and the electrons in the combined stream; and, means for stopping the O(-) ions and the electrons and for allowing only the ground-state O atoms to continue as the source of the atoms of interest. The method and apparatus are also adaptable for producing other ground-state atoms and/or molecules.

Probing dark energy with atom interferometry

NASA Astrophysics Data System (ADS)

Burrage, Clare; Copeland, Edmund J.; Hinds, E. A.

2015-03-01

Theories of dark energy require a screening mechanism to explain why the associated scalar fields do not mediate observable long range fifth forces. The archetype of this is the chameleon field. Here we show that individual atoms are too small to screen the chameleon field inside a large high-vacuum chamber, and therefore can detect the field with high sensitivity. We derive new limits on the chameleon parameters from existing experiments, and show that most of the remaining chameleon parameter space is readily accessible using atom interferometry.

Electron-driven excitation of O 2 under night-time auroral conditions: Excited state densities and band emissions

NASA Astrophysics Data System (ADS)

Jones, D. B.; Campbell, L.; Bottema, M. J.; Teubner, P. J. O.; Cartwright, D. C.; Newell, W. R.; Brunger, M. J.

2006-01-01

Electron impact excitation of vibrational levels in the ground electronic state and seven excited electronic states in O 2 have been simulated for an International Brightness Coefficient-Category 2+ (IBC II+) night-time aurora, in order to predict O 2 excited state number densities and volume emission rates (VERs). These number densities and VERs are determined as a function of altitude (in the range 80-350 km) in the present study. Recent electron impact excitation cross-sections for O 2 were combined with appropriate altitude dependent IBC II+ auroral secondary electron distributions and the vibrational populations of the eight O 2 electronic states were determined under conditions of statistical equilibrium. Pre-dissociation, atmospheric chemistry involving atomic and molecular oxygen, radiative decay and quenching of excited states were included in this study. This model predicts relatively high number densities for the X3Σg-(v'⩽4),a1Δandb1Σg+ metastable electronic states and could represent a significant source of stored energy in O 2* for subsequent thermospheric chemical reactions. Particular attention is directed towards the emission intensities of the infrared (IR) atmospheric (1.27 μm), Atmospheric (0.76 μm) and the atomic oxygen 1S→ 1D transition (5577 Å) lines and the role of electron-driven processes in their origin. Aircraft, rocket and satellite observations have shown both the IR atmospheric and Atmospheric lines are dramatically enhanced under auroral conditions and, where possible, we compare our results to these measurements. Our calculated 5577 Å intensity is found to be in good agreement with values independently measured for a medium strength IBC II+ aurora.

Routes to formation of highly excited neutral atoms in the break-up of strongly driven hydrogen molecule

NASA Astrophysics Data System (ADS)

Emmanouilidou, Agapi

2012-06-01

We present a theoretical quasiclassical treatment of the formation, during Coulomb explosion, of highly excited neutral H atoms for strongly-driven hydrogen molecule. This process, where after the laser field is turned off, one electron escapes to the continuum while the other occupies a Rydberg state, was recently reported in an experimental study in Phys. Rev. Lett 102, 113002 (2009). We find that two-electron effects are important in order to correctly account for all pathways leading to highly excited neutral hydrogen formation [1]. We identify two pathways where the electron that escapes to the continuum does so either very quickly or after remaining bound for a few periods of the laser field. These two pathways of highly excited neutral H formation have distinct traces in the probability distribution of the escaping electron momentum components. [4pt] [1] A. Emmanouilidou, C. Lazarou, A. Staudte and U. Eichmann, Phys. Rev. A (Rapid) 85 011402 (2012).

Spin-Orbital Excitations in Ca2 RuO4 Revealed by Resonant Inelastic X-Ray Scattering

NASA Astrophysics Data System (ADS)

Das, L.; Forte, F.; Fittipaldi, R.; Fatuzzo, C. G.; Granata, V.; Ivashko, O.; Horio, M.; Schindler, F.; Dantz, M.; Tseng, Yi; McNally, D. E.; Rønnow, H. M.; Wan, W.; Christensen, N. B.; Pelliciari, J.; Olalde-Velasco, P.; Kikugawa, N.; Neupert, T.; Vecchione, A.; Schmitt, T.; Cuoco, M.; Chang, J.

2018-01-01

The strongly correlated insulator Ca2 RuO4 is considered as a paradigmatic realization of both spin-orbital physics and a band-Mott insulating phase, characterized by orbitally selective coexistence of a band and a Mott gap. We present a high resolution oxygen K -edge resonant inelastic x-ray scattering study of the antiferromagnetic Mott insulating state of Ca2 RuO4 . A set of low-energy (about 80 and 400 meV) and high-energy (about 1.3 and 2.2 eV) excitations are reported, which show strong incident light polarization dependence. Our results strongly support a spin-orbit coupled band-Mott scenario and explore in detail the nature of its exotic excitations. Guided by theoretical modeling, we interpret the low-energy excitations as a result of composite spin-orbital excitations. Their nature unveils the intricate interplay of crystal-field splitting and spin-orbit coupling in the band-Mott scenario. The high-energy excitations correspond to intra-atomic singlet-triplet transitions at an energy scale set by Hund's coupling. Our findings give a unifying picture of the spin and orbital excitations in the band-Mott insulator Ca2 RuO4 .

A program to compute the two-step excitation of mesospheric sodium atoms for the Polychromatic Laser Guide Star Project

NASA Astrophysics Data System (ADS)

Bellanger, Véronique; Courcelle, Arnaud; Petit, Alain

2004-09-01

A program to compute the two-step excitation of sodium atoms ( 3S→3P→4D) using the density-matrix formalism is presented. The BEACON program calculates population evolution and the number of photons emitted by fluorescence from the 3P, 4D, 4P, 4S levels. Program summaryTitle of program: BEACON Catalogue identifier:ADSX Program Summary URL:http://cpc.cs.qub.ac.uk/cpc/summaries/ADSX Program obtainable from: CPC Program Library, Queen's University of Belfast, N. Ireland Licensing provisions: none Operating systems under which the program has been tested: Win; Unix Programming language used: FORTRAN 77 Memory required to execute with typical data: 1 Mw Number of bits in a word: 32 Number of processors used: 1 (a parallel version of this code is also available and can be obtained on request) Number of lines in distributed program, including test data, etc.: 29 287 Number of bytes in distributed program, including test data, etc.: 830 331 Distribution format: tar.gz CPC Program Library subprograms used: none Nature of physical problem: Resolution of the Bloch equations in the case of the two-step laser excitation of sodium atoms. Method of solution: The program BEACON calculates the evolution of level population versus time using the density-matrix formalism. The number of photons emitted from the 3P, 4D and 4P levels is calculated using the branching ratios and the level lifetimes. Restriction on the complexity of the problem: Since the backscatter emission is calculated after the excitation process, excitation with laser pulse duration longer than the 4D level lifetime cannot be rigorously treated. Particularly, cw laser excitation cannot be calculated with this code. Typical running time:12 h

Coulomb excitation of 206Hg at relativistic energies

NASA Astrophysics Data System (ADS)

Alexander, Tom

The region of the nuclear chart surrounding the doubly-magic nucleus 208Pb provides a key area to constrain and develop contemporary nuclear structure models. One aspect of particular interest is the transition strength of the first excited 2+ state in even-even nuclei; this work describes the measurement of this value for the case of 206Hg, where the Z=80 line meets the N=126 shell closure. The nuclei of interest were synthesized using relativistic-energy projectile fragmentation at the GSI facility in Germany. They were produced in the fragmentation of a primary 208Pb beam at an energy of 1 GeV per nucleon, and separated and identifed using the Fragment Separator. The secondary beams with an energy of 140 MeV per nucleon were Coulomb excited on a secondary target of 400 mg/cm. 2 gold. Gamma-rays were detected with the Advanced GAmma Tracking Array (AGATA). The precise scattering angle for Doppler-correction was determined with position information from the Lund-York-Cologne-CAlorimeter(LYCCA). Using the sophisticated tracking algorithm native to AGATA in conjunction with pulse-shape analysis, a precise Doppler-correction is performed on the gamma spectra, and using a complex n-dimensional analysis, the B(E2) value for 206Hg is extracted relative to the known value also measured in 206Pb. A total of 409 million 206Hg particles were measured, and a cross-section of 50 mb was determined for the 2+ state at 1068 keV. The measurement of the B(E2) transition strength was found to be 1.109 W.u. This result is compared to a number of theoretical calculations, including two Gogny forces, and a modified shell model parametrization and is found to be smaller than all calculated estimations, implying that the first excited 2. + state in . {206}Hg is uncollective in nature.

Time resolved laser induced fluorescence on argon intermediate pressure microwave discharges: Measuring the depopulation rates of the 4p and 5p excited levels as induced by electron and atom collisions

NASA Astrophysics Data System (ADS)

Palomares, J. M.; Graef, W. A. A. D.; Hübner, S.; van der Mullen, J. J. A. M.

2013-10-01

The reaction kinetics in the excitation space of Ar is explored by means of Laser Induced Fluorescence (LIF) experiments using the combination of high rep-rate YAG-Dye laser systems with a well defined and easily controllable surfatron induced plasma setup. The high rep-rate favors the photon statistics while the low energy per pulse avoids intrusive plasma laser interactions. An analysis shows that, despite the low energy per pulse, saturation can still be achieved even when the geometrical overlap and spectral overlap are optimal. Out of the various studies that can be performed with this setup we confine the current paper to the study of the direct responses to the laser pump action of three 4p and one 5p levels of the Ar system. By changing the plasma in a controlled way one gets for these levels the rates of electron and atom quenching and therewith the total destruction rates of electron and atom collisions. Comparison with literature shows that the classical hard sphere collision rate derived for hydrogen gives a good description for the observed electron quenching (e-quenching) in Ar whereas for heavy particle quenching (a-quenching) this agreement was only found for the 5p level. An important parameter in the study of electron excitation kinetics is the location of the boundary in the atomic system for which the number of electron collisions per radiative life time equals unity. It is observed that for the Ar system this boundary is positioned lower than what is expected on grounds of H-like formulas.

Atomic oxygen beam source for erosion simulation

NASA Technical Reports Server (NTRS)

Cuthbertson, J. W.; Langer, W. D.; Motley, R. W.; Vaughn, J. A.

1991-01-01

A device for the production of low energy (3 to 10 eV) neutral atomic beams for surface modification studies is described that reproduces the flux of atomic oxygen in low Earth orbit. The beam is produced by the acceleration of plasma ions onto a negatively biased plate of high-Z metal; the ions are neutralized and reflected by the surface, retaining some fraction of their incident kinetic energy, forming a beam of atoms. The plasma is generated by a coaxial RF exciter which produces a magnetically-confined (4 kG) plasma column. At the end of the column, ions fall through the sheath to the plate, whose bias relative to the plasma can be varied to adjust the beam energy. The source provides a neutral flux approximately equal to 5 x 10(exp 16)/sq cm at a distance of 9 cm and a fluence approximately equal to 10(exp 20)/sq cm in five hours. The composition and energy of inert gas beams was diagnosed using a mass spectometer/energy analyzer. The energy spectra of the beams demonstrate energies in the range 5 to 15 eV, and qualitatively show expected dependences upon incident and reflecting atom species and potential drop. Samples of carbon film, carbon-based paint, Kapton, mylar, and teflon exposed to atomic O beams show erosion quite similar to that observed in orbit on the space shuttle.

Probing optical excitations in chevron-like armchair graphene nanoribbons.

PubMed

Denk, Richard; Lodi-Rizzini, Alberto; Wang, Shudong; Hohage, Michael; Zeppenfeld, Peter; Cai, Jinming; Fasel, Roman; Ruffieux, Pascal; Berger, Reinhard Franz Josef; Chen, Zongping; Narita, Akimitsu; Feng, Xinliang; Müllen, Klaus; Biagi, Roberto; De Renzi, Valentina; Prezzi, Deborah; Ruini, Alice; Ferretti, Andrea

2017-11-30

The bottom-up fabrication of graphene nanoribbons (GNRs) has opened new opportunities to specifically tune their electronic and optical properties by precisely controlling their atomic structure. Here, we address excitation in GNRs with periodic structural wiggles, the so-called chevron GNRs. Based on reflectance difference and high-resolution electron energy loss spectroscopies together with ab initio simulations, we demonstrate that their excited-state properties are of excitonic nature. The spectral fingerprints corresponding to different reaction stages in their bottom-up fabrication are also unequivocally identified, allowing us to follow the exciton build-up from the starting monomer precursor to the final GNR structure.

Laser-Excited Atomic Fluorescence and Ionization in a Graphite Furnace for the Determination of Metals and Nonmetals

NASA Astrophysics Data System (ADS)

Butcher, David James

1990-01-01

Here is reported novel instrumentation for atomic spectrometry that combined the use of a pulsed laser system as the light source and an electrothermal atomizer as the atom cell. The main goal of the research was to develop instrumentation that was more sensitive for elemental analysis than commercially available instruments and could be used to determine elements in real sample matrices. Laser excited atomic fluorescence spectrometry (LEAFS) in an electrothermal atomizer (ETA) was compared to ETA atomic absorption spectrometry (AAS) for the determination of thallium, manganese, and lead in food and agricultural standard reference materials (SRMs). Compared to ETA AAS, ETA LEAFS has a longer linear dynamic range (LDR) (5-7 orders of magnitude compared to 2-3 orders of magnitude) and higher sensitivity (10 ^{-16} to 10^{ -14} g as compared to 10^{ -13} to 10^{-11} g). Consequently, ETA LEAFS allows elemental analysis to be done over a wider range of concentrations with less dilution steps. Thallium was accurately determined in biological samples by ETA LEAFS at amounts five to one hundred times below the ETA AAS detection limit. ETA AAS and ETA LEAFS were compared for the determination of lead and manganese, and in general, the accuracies and precisions of ETA AAS were the same, with typical precisions between 3% and 6%. Fluorine was determined using laser excited molecular fluorescence spectrometry (LEMOFS) in an ETA. Molecular fluorescence from magnesium fluoride was collected, and the detection limit of 0.3 pg fluorine was two to six orders of magnitude more sensitive than other methods commonly used for the determination of fluorine. Significant interferences from ions were observed, but the sensitivity was high enough that fluorine could be determined in freeze dried urine SRMs by diluting the samples by a factor of one hundred to remove the interferences. Laser enhanced ionization (LEI) in an ETA was used for the determination of metals. For thallium, indium

Emission- and fluorescence-spectroscopic investigation of a glow discharge plasma: absolute number density of radiative and nonradiative atoms in the negative glow.

PubMed

Takubo, Y; Sato, T; Asaoka, N; Kusaka, K; Akiyama, T; Muroo, K; Yamamoto, M

2008-01-01

The excited-state atom densities in the negative glow of a direct-current glow discharge are derived from the spectral-line intensity of radiative atoms and the resonance-fluorescence photon flux of nonradiative atoms. The discharge is operated in a helium-argon gas mixture (molar fraction ratio 91:9; total gas pressure 5 Torr) at a dc current of 0.7-1.2 mA. The observations are made in the region of the maximum luminance in the cathode region, where high-energy electrons accelerated in the cathode fall are injected into the negative glow. The emission intensities of the He I, He II, Ar I, and Ar II spectral lines are measured with a calibrated tungsten ribbon lamp as an absolute spectral-radiance standard. Fluorescence photons scattered by helium and argon atoms in the metastable state and argon atoms in the resonance state are detected by the laser-induced fluorescence (LIF) method with the Rayleigh scattering of nitrogen molecules as an absolute standard of scattering cross section. The laser absorption method is incorporated to confirm the result of the LIF measurement. Excitation energies of the measured spectral lines range from 11.6 (Ar I) to 75.6 eV (He II), where the excitation energy is measured from the ground state of the neutral atom on the assumption that, in the plasma of this study, both the neutral and the ionic lines are excited by electron impact in a single-step process from the ground state of the corresponding neutral atoms. Experimental evidence is shown for the validity of this assumption.

Nonperturbative theory for the dispersion self-energy of atoms

NASA Astrophysics Data System (ADS)

Thiyam, Priyadarshini; Persson, C.; Brevik, I.; Sernelius, Bo E.; Boström, Mathias

2014-11-01

We go beyond the approximate series expansions used in the dispersion theory of finite-size atoms. We demonstrate that a correct, and nonperturbative, theory dramatically alters the dispersion self-energies of atoms. The nonperturbed theory gives as much as 100 % corrections compared to the traditional series-expanded theory for the smaller noble gas atoms.

Effects of Low-Energy Excitations on Spectral Properties at Higher Binding Energy: The Metal-Insulator Transition of VO2

NASA Astrophysics Data System (ADS)

Gatti, Matteo; Panaccione, Giancarlo; Reining, Lucia

2015-03-01

The effects of electron interaction on spectral properties can be understood in terms of coupling between excitations. In transition-metal oxides, the spectral function close to the Fermi level and low-energy excitations between d states have attracted particular attention. In this work we focus on photoemission spectra of vanadium dioxide over a wide (10 eV) range of binding energies. We show that there are clear signatures of the metal-insulator transition over the whole range due to a cross coupling of the delocalized s and p states with low-energy excitations between the localized d states. This coupling can be understood by advanced calculations based on many-body perturbation theory in the G W approximation. We also advocate the fact that tuning the photon energy up to the hard-x-ray range can help to distinguish fingerprints of correlation from pure band-structure effects.

CC2 oscillator strengths within the local framework for calculating excitation energies (LoFEx).

PubMed

Baudin, Pablo; Kjærgaard, Thomas; Kristensen, Kasper

2017-04-14

In a recent work [P. Baudin and K. Kristensen, J. Chem. Phys. 144, 224106 (2016)], we introduced a local framework for calculating excitation energies (LoFEx), based on second-order approximated coupled cluster (CC2) linear-response theory. LoFEx is a black-box method in which a reduced excitation orbital space (XOS) is optimized to provide coupled cluster (CC) excitation energies at a reduced computational cost. In this article, we present an extension of the LoFEx algorithm to the calculation of CC2 oscillator strengths. Two different strategies are suggested, in which the size of the XOS is determined based on the excitation energy or the oscillator strength of the targeted transitions. The two strategies are applied to a set of medium-sized organic molecules in order to assess both the accuracy and the computational cost of the methods. The results show that CC2 excitation energies and oscillator strengths can be calculated at a reduced computational cost, provided that the targeted transitions are local compared to the size of the molecule. To illustrate the potential of LoFEx for large molecules, both strategies have been successfully applied to the lowest transition of the bivalirudin molecule (4255 basis functions) and compared with time-dependent density functional theory.

Plant Cell Imaging Based on Nanodiamonds with Excitation-Dependent Fluorescence

NASA Astrophysics Data System (ADS)

Su, Li-Xia; Lou, Qing; Jiao, Zhen; Shan, Chong-Xin

2016-09-01

Despite extensive work on fluorescence behavior stemming from color centers of diamond, reports on the excitation-dependent fluorescence of nanodiamonds (NDs) with a large-scale redshift from 400 to 620 nm under different excitation wavelengths are so far much fewer, especially in biological applications. The fluorescence can be attributed to the combined effects of the fraction of sp2-hybridized carbon atoms among the surface of the fine diamond nanoparticles and the defect energy trapping states on the surface of the diamond. The excitation-dependent fluorescent NDs have been applied in plant cell imaging for the first time. The results reported in this paper may provide a promising route to multiple-color bioimaging using NDs.

Plant Cell Imaging Based on Nanodiamonds with Excitation-Dependent Fluorescence.

PubMed

Su, Li-Xia; Lou, Qing; Jiao, Zhen; Shan, Chong-Xin

2016-12-01

Despite extensive work on fluorescence behavior stemming from color centers of diamond, reports on the excitation-dependent fluorescence of nanodiamonds (NDs) with a large-scale redshift from 400 to 620 nm under different excitation wavelengths are so far much fewer, especially in biological applications. The fluorescence can be attributed to the combined effects of the fraction of sp(2)-hybridized carbon atoms among the surface of the fine diamond nanoparticles and the defect energy trapping states on the surface of the diamond. The excitation-dependent fluorescent NDs have been applied in plant cell imaging for the first time. The results reported in this paper may provide a promising route to multiple-color bioimaging using NDs.

State-specific transport properties of electronically excited Ar and C

NASA Astrophysics Data System (ADS)

Istomin, V. A.; Kustova, E. V.

2018-05-01

In the present study, a theoretical model of state-resolved transport properties in electronically excited atomic species developed earlier is applied to argon and carbon atomic species. It is shown that for Ar and C, similarly to the case of atomic nitrogen and oxygen, the Slater-like models can be applied to calculate diameters of electronically excited atoms. Using the Slater-like model it is shown that for half-filled N (2 px1py1pz1) and full-filled Ar (3 px2py2pz2) electronic shells the growth of atomic radius goes slowly compared to C (2 px1py1) and O (2 px2py1pz1). The effect of collision diameters on the transport properties of Ar and C is evaluated. The influence of accounted number of electronic levels on the transport coefficients is examined for the case of Boltzmann distributions over electronic energy levels. It is emphasized that in the temperature range 1000-14000 K, for Boltzmann-like distributions over electronic states the number of accounted electronic levels do not influence the transport coefficients. Contrary to this, for higher temperatures T > 14000 K this effect becomes of importance, especially for argon.

Low-energy d-d excitations in MnO studied by resonant x-ray fluorescence spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Butorin, S.M.; Guo, J.; Magnuson, M.

1997-04-01

Resonant soft X-ray emission spectroscopy has been demonstrated to possess interesting abilities for studies of electronic structure in various systems, such as symmetry probing, alignment and polarization dependence, sensitivity to channel interference, etc. In the present abstract the authors focus on the feasibility of resonant soft X-ray emission to probe low energy excitations by means of resonant electronic X-ray Raman scattering. Resonant X-ray emission can be regarded as an inelastic scattering process where a system in the ground state is transferred to a low excited state via a virtual core excitation. The energy closeness to a core excitation of themore » exciting radiation enhances the (generally) low probability for inelastic scattering at these wavelengths. Therefore soft X-ray emission spectroscopy (in resonant electronic Raman mode) can be used to study low energy d-d excitations in transition metal systems. The involvement of the intermediate core state allows one to use the selection rules of X-ray emission, and the appearance of the elastically scattered line in the spectra provides the reference to the ground state.« less

Comparison of Atomic Oxygen Erosion Yields of Materials at Various Energy and Impact Angles

NASA Technical Reports Server (NTRS)

Banks, Bruce A.; Waters, Deborah L.; Thorson, Stephen D.; deGroh, Kim, K.; Snyder, Aaron; Miller, Sharon

2006-01-01

The atomic oxygen erosion yields of various materials, measured in volume of material oxidized per incident atomic oxygen atom, are compared to the commonly accepted standard of Kapton H (DuPont) polyimide. The ratios of the erosion yield of Kapton H to the erosion yield of various materials are not consistent at different atomic oxygen energies. Although it is most convenient to use isotropic thermal energy RF plasma ashers to assess atomic oxygen durability, the results can be misleading because the relative erosion rates at thermal energies are not necessarily the same as low Earth orbital (LEO) energies of approx.4.5 eV. An experimental investigation of the relative atomic oxygen erosion yields of a wide variety of polymers and carbon was conducted using isotropic thermal energy (approx.0.1 eV) and hyperthermal energy (approx.70 eV) atomic oxygen using an RF plasma asher and an end Hall ion source. For hyperthermal energies, the atomic oxygen erosion yields relative to normal incident Kapton H were compared for sweeping atomic oxygen arrival with that of normal incidence arrival. The results of isotropic thermal energy, normal incident, and sweeping incident atomic oxygen are also compared with measured or projected LEO values.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Samanta, A.; Fessenden, R.W.

1989-07-27

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

History of the United States Atomic Energy Commission. Volume II. 1947 / 1952, Atomic Shield

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hewlett, Richard G.; Duncan, Francis

1972-01-01

Sponsored by the Historical Advisory Committee of the Atomic Energy Commission (AEC), this 2-volume series provides an unclassified history of the AEC. Volume I is subtitled ''The New World'' and covers the AEC from 1939 through 1946. This volume, Volume II, is subtitled ''Atomic Shield'' and covers the years 1947 through 1952.

Control of base-excited dynamical systems through piezoelectric energy harvesting absorber

NASA Astrophysics Data System (ADS)

Abdelmoula, H.; Dai, H. L.; Abdelkefi, A.; Wang, L.

2017-09-01

The spring-mass absorber usually offers a good control to dynamical systems under direct base excitations for a specific value of the excitation frequency. As the vibrational energy of a primary dynamical system is transferred to the absorber, it gets dissipated. In this study, this energy is no longer dissipated but converted to available electrical power by designing efficient energy harvesters. A novel design of a piezoelectric beam installed inside an elastically-mounted dynamical system undergoing base excitations is considered. A design is carried out in order to determine the properties and dimensions of the energy harvester with the constraint of simultaneously decreasing the oscillating amplitudes of the primary dynamical system and increasing the harvested power of the energy harvesting absorber. An analytical model for the coupled system is constructed using Euler-Lagrange principle and Galerkin discretization. Different strategies for controlling the primary structure displacement and enhancing the harvested power as functions of the electrical load resistance and thickness of the beam substrate are performed. The linear polynomial approximation of the system’s key parameters as a function of the beam’s substrate thickness is first carried out. Then, the gradient method is applied to determine the adequate values of the electrical load resistance and thickness of the substrate under the constraints of minimizing the amplitudes of the primary structure or maximizing the levels of the harvested power. After that, an iterative strategy is considered in order to simultaneously minimize the amplitudes of the primary structure and maximize the levels of the harvested power as functions of the thickness of the substrate and electrical load resistance. In addition to harmonic excitations, the coupled system subjected to a white noise is explored. Through this analysis, the load resistance and thickness of the substrate of the piezoelectric energy harvester

Light absorption and excitation energy transfer calculations in primitive photosynthetic bacteria

NASA Astrophysics Data System (ADS)

Komatsu, Yu; Kayanuma, Megumi; Shoji, Mitsuo; Yabana, Kazuhiro; Shiraishi, Kenji; Umemura, Masayuki

2015-06-01

In photosynthetic organisms, light energy is converted into chemical energy through the light absorption and excitation energy transfer (EET) processes. These processes start in light-harvesting complexes, which contain special photosynthetic pigments. The exploration of unique mechanisms in light-harvesting complexes is directly related to studies, such as artificial photosynthesis or biosignatures in astrobiology. We examined, through ab initio calculations, the light absorption and EET processes using cluster models of light-harvesting complexes in purple bacteria (LH2). We evaluated absorption spectra and energy transfer rates using the LH2 monomer and dimer models to reproduce experimental results. After the calibration tests, a LH2 aggregation model, composed of 7 or 19 LH2s aligned in triangle lattice, was examined. We found that the light absorption is red shifted and the energy transfer becomes faster as the system size increases. We also found that EET is accelerated by exchanging the central pigments to lower energy excited pigments. As an astrobiological application, we calculated light absorptions efficiencies of the LH2 in different photoenvironments.

Resonant Raman scattering in single crystal of congruent LiTaO 3 : Effect of excitation energy

NASA Astrophysics Data System (ADS)

Bhaumik, Indranil; Kumar, Shailendra; Ganesamoorthy, S.; Bhatt, R.; Karnal, A. K.; Raja Sekhar, B. N.

2011-12-01

Large dispersion in the peak position of the OH - stretching mode (˜687.9 and ˜2167.7 cm -1/eV for fundamental and 3rd harmonic, respectively) is observed by Resonance Raman studies in congruent lithium tantalate single crystal under varying excitation energies. This is explained by considering the involvement of multiple LO phonons in the interaction with OH - stretching vibration and the resonantly excited electrons. The intensity of the peaks is also found to vary with the excitation energy. FWHM increases with the increase in excitation energy because of individual contributions of the increasing number of resonance steps to the broadening.

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

Performance of an Optimally Tuned Range-Separated Hybrid Functional for 0-0 Electronic Excitation Energies.

PubMed

Jacquemin, Denis; Moore, Barry; Planchat, Aurélien; Adamo, Carlo; Autschbach, Jochen

2014-04-08

Using a set of 40 conjugated molecules, we assess the performance of an "optimally tuned" range-separated hybrid functional in reproducing the experimental 0-0 energies. The selected protocol accounts for the impact of solvation using a corrected linear-response continuum approach and vibrational corrections through calculations of the zero-point energies of both ground and excited-states and provides basis set converged data thanks to the systematic use of diffuse-containing atomic basis sets at all computational steps. It turns out that an optimally tuned long-range corrected hybrid form of the Perdew-Burke-Ernzerhof functional, LC-PBE*, delivers both the smallest mean absolute error (0.20 eV) and standard deviation (0.15 eV) of all tested approaches, while the obtained correlation (0.93) is large but remains slightly smaller than its M06-2X counterpart (0.95). In addition, the efficiency of two other recently developed exchange-correlation functionals, namely SOGGA11-X and ωB97X-D, has been determined in order to allow more complete comparisons with previously published data.

l- and n-changing collisions during interaction of a pulsed beam of Li Rydberg atoms with CO2

NASA Astrophysics Data System (ADS)

Dubreuil, B.; Harnafi, M.

1989-07-01

The pulsed Li atomic beam produced in our experiment is based on controlled transversely-excited-atmospheric CO2 laser-induced ablation of a Li metal target. The atomic beam is propagated in vacuum or in CO2 gas at low pressure. Atoms in the beam are probed by laser-induced fluorescence spectroscopy. This allows the determination of time-of-flight and velocity distributions. Li Rydberg states (n=5-13) are populated in the beam by two-step pulsed-laser excitation. The excited atoms interact with CO2 molecules. l- and n-changing cross sections are deduced from the time evolution of the resonant or collision-induced fluorescence following this selective excitation. l-changing cross sections of the order of 104 AṦ are measured; they increase with n as opposed to the plateau observed for Li* colliding with a diatomic molecule. This behavior is qualitatively well explained in the framework of the free-electron model. n-->n' changing processes with large cross sections (10-100 AṦ) are also observed even in the case of large electronic energy change (ΔEnn'>103 cm-1). These results can be interpreted in terms of resonant-electronic to vibrational energy transfers between Li Rydberg states and CO2 vibrational modes.

Photodissociation Efficiency Spectroscopy Study of the Rydberg Excited Ion-Pair States of Carbon Dioxide

NASA Astrophysics Data System (ADS)

Feng, Qiang; Xu, Yun-Feng; Sun, Jin-Da; Tian, Shan-Xi; Shan, Xiao-Bin; Liu, Fu-Yi; Sheng, Liu-Si

2009-10-01

Photodissociation efficiency spectrum of anionic oxygen atom produced via ion-pair dissociations of carbon dioxide is recorded by means of the synchrotron radiation excitation (XUV photon energy 17.40-20.00 eV). The present spectrum is assigned as the Rydberg-like excited ion-pair states, i.e., Tanaka-Ogawa and Henning series, tilde C2Σg+ (CO+2) vibrational ground-state and excitation series. Three Rydberg series, npσu, npπu, and nfu, converging to tilde C2Σg+ (0, 0, 0), show the higher cross sections.

Using atom interferometry to detect dark energy

NASA Astrophysics Data System (ADS)

Burrage, Clare; Copeland, Edmund J.

2016-04-01

We review the tantalising prospect that the first evidence for the dark energy driving the observed acceleration of the universe on giga-parsec scales may be found through metre scale laboratory-based atom interferometry experiments. To do that, we first introduce the idea that scalar fields could be responsible for dark energy and show that in order to be compatible with fifth force constraints, these fields must have a screening mechanism which hides their effects from us within the solar system. Particular emphasis is placed on one such screening mechanism known as the chameleon effect where the field's mass becomes dependent on the environment. The way the field behaves in the presence of a spherical source is determined and we then go on to show how in the presence of the kind of high vacuum associated with atom interferometry experiments, and when the test particle is an atom, it is possible to use the associated interference pattern to place constraints on the acceleration due to the fifth force of the chameleon field - this has already been used to rule out large regions of the chameleon parameter space and maybe one day will be able to detect the force due to the dark energy field in the laboratory.

The pair-production channel in atomic processes

NASA Astrophysics Data System (ADS)

Belkacem, Ali; Sørensen, Allan H.

2006-06-01

Assisted by the creation of electron-positron pairs, new channels for ionization, excitation, and charge transfer open in atomic collisions when the energy is raised to relativistic values. At extreme energies these pair-production channels usually dominate the "traditional" contributions to cross sections that involve only "positive-energy" electrons. An extensive body of theoretical and experimental work has been performed over the last two decades to investigate charge-changing processes catalyzed by pair production in relativistic heavy ion collisions. We review some of these studies.

An accurate and efficient method to predict the electronic excitation energies of BODIPY fluorescent dyes.

PubMed

Wang, Jia-Nan; Jin, Jun-Ling; Geng, Yun; Sun, Shi-Ling; Xu, Hong-Liang; Lu, Ying-Hua; Su, Zhong-Min

2013-03-15

Recently, the extreme learning machine neural network (ELMNN) as a valid computing method has been proposed to predict the nonlinear optical property successfully (Wang et al., J. Comput. Chem. 2012, 33, 231). In this work, first, we follow this line of work to predict the electronic excitation energies using the ELMNN method. Significantly, the root mean square deviation of the predicted electronic excitation energies of 90 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) derivatives between the predicted and experimental values has been reduced to 0.13 eV. Second, four groups of molecule descriptors are considered when building the computing models. The results show that the quantum chemical descriptions have the closest intrinsic relation with the electronic excitation energy values. Finally, a user-friendly web server (EEEBPre: Prediction of electronic excitation energies for BODIPY dyes), which is freely accessible to public at the web site: http://202.198.129.218, has been built for prediction. This web server can return the predicted electronic excitation energy values of BODIPY dyes that are high consistent with the experimental values. We hope that this web server would be helpful to theoretical and experimental chemists in related research. Copyright © 2012 Wiley Periodicals, Inc.

Determination of the number density of excited and ground Zn atoms during rf magnetron sputtering of ZnO target

DOE Office of Scientific and Technical Information (OSTI.GOV)

Maaloul, L.; Gangwar, R. K.; Stafford, L., E-mail: luc.stafford@umontreal.ca

2015-07-15

A combination of optical absorption spectroscopy (OAS) and optical emission spectroscopy measurements was used to monitor the number density of Zn atoms in excited 4s4p ({sup 3}P{sub 2} and {sup 3}P{sub 0}) metastable states as well as in ground 4s{sup 2} ({sup 1}S{sub 0}) state in a 5 mTorr Ar radio-frequency (RF) magnetron sputtering plasma used for the deposition of ZnO-based thin films. OAS measurements revealed an increase by about one order of magnitude of Zn {sup 3}P{sub 2} and {sup 3}P{sub 0} metastable atoms by varying the self-bias voltage on the ZnO target from −115 to −300 V. Over themore » whole range of experimental conditions investigated, the triplet-to-singlet metastable density ratio was 5 ± 1, which matches the statistical weight ratio of these states in Boltzmann equilibrium. Construction of a Boltzmann plot using all Zn I emission lines in the 200–500 nm revealed a constant excitation temperature of 0.33 ± 0.04 eV. In combination with measured populations of Zn {sup 3}P{sub 2} and {sup 3}P{sub 0} metastable atoms, this temperature was used to extrapolate the absolute number density of ground state Zn atoms. The results were found to be in excellent agreement with those obtained previously by actinometry on Zn atoms using Ar as the actinometer gas [L. Maaloul and L. Stafford, J. Vac. Sci. Technol., A 31, 061306 (2013)]. This set of data was then correlated to spectroscopic ellipsometry measurements of the deposition rate of Zn atoms on a Si substrate positioned at 12 cm away from the ZnO target. The deposition rate scaled linearly with the number density of Zn atoms. In sharp contrast with previous studies on RF magnetron sputtering of Cu targets, these findings indicate that metastable atoms play a negligible role on the plasma deposition dynamics of Zn-based coatings.« less