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Sample records for near-threshold rovibrational excitation

  1. Near-threshold vibrational excitation of acetylene by positron impact

    SciTech Connect

    Oliveira, Eliane M. de; Lima, Marco A. P.; Sanchez, Sergio d'A.; Varella, Marcio T. do N.

    2010-01-15

    We report vibrational excitation cross sections for C-C and C-H symmetric stretch modes of acetylene by positron impact. The contribution of these infrared inactive modes to the annihilation parameter is also addressed. The Feshbach projection operator approach was employed to vibrationally resolve e{sup +}-acetylene scattering phase shifts obtained with the Schwinger multichannel method. The present results point out a virtual state pole at the equilibrium geometry of acetylene that becomes a bound state as either bond is stretched, in qualitative agreement with previous calculations for small hydrocarbons. The vibrational couplings are stronger for the C-C mode, giving rise to a bound state pole within the Franck-Condon region of the vibrational ground state. These bound and virtual states give rise to sharp threshold structures (vibrational resonances) in both the vibrational excitation cross sections and the annihilation parameter (Z{sub eff}). We found fair agreement between the present calculations and previously reported e{sup +}-acetylene vibrational excitation cross sections.

  2. Near Threshold Excitation of Molecular Nitrogen: Benchmarking Cross Sections for Upper Atmospheres

    NASA Astrophysics Data System (ADS)

    Malone, C. P.; Johnson, P. V.; Hein, J. D.; Grisanti, B.; Khakoo, M. A.

    2013-12-01

    Molecular nitrogen is the major component in the atmospheres of Earth, Titan, and Triton. The airglow emissions of N2 from the atmospheres of Earth and planetary satellites have been extensively observed. Accurate, consistent cross section data is a necessity for accurate models of how upper atmospheres behave. We present electron energy-loss (EEL) derived excitation cross sections for near-threshold electron impact of N2. Differential cross sections (DCSs) and integral cross sections (ICSs) were obtained by unfolding EEL spectra in the ~6-11eV range for the A 3Σu+, B 3Πg, W 3Δu, B‧ 3Σu-, a‧ 1Σu-, a 1Πg, w 1Δu, and C 1Πu electronic states over the ~15-130° scattering angular range. Vibrationally-resolved DCSs and ICSs were obtained for stronger vibronic transitions, including the a 1Πg state, which generates the atmospherically important Lyman-Birge-Hopfield (LBH) emissions. The summed near-threshold excitation cross sections (A+...+C) generally are larger than previous measurements. Acknowledgement: This work was performed at CSUF and JPL, Caltech, under contract with NASA. We gratefully acknowledge financial support through NASA's PATM and GEO programs and NSF-PHY-RUI-0965793.

  3. Photoionization cross section measurements of the excited states of cobalt in the near-threshold region

    SciTech Connect

    Zheng, Xianfeng Zhou, Xiaoyu; Cheng, Zaiqi; Jia, Dandan; Qu, Zehua; Yao, Guanxin; Zhang, Xianyi; Cui, Zhifeng

    2014-10-15

    We present measurements of photoionization cross-sections of the excited states of cobalt using a two-color, two-step resonance ionization technique in conjunction with a molecular beam time of flight (TOF) mass spectrometer. The atoms were produced by the laser vaporization of a cobalt rod, coupled with a supersonic gas jet. The absolute photoionization cross-sections at threshold and near-threshold regions (0-1.2 eV) were measured, and the measured values ranged from 4.2±0.7 Mb to 10.5±1.8 Mb. The lifetimes of four odd parity energy levels are reported for the first time.

  4. Prestimulus Network Integration of Auditory Cortex Predisposes Near-Threshold Perception Independently of Local Excitability

    PubMed Central

    Leske, Sabine; Ruhnau, Philipp; Frey, Julia; Lithari, Chrysa; Müller, Nadia; Hartmann, Thomas; Weisz, Nathan

    2015-01-01

    An ever-increasing number of studies are pointing to the importance of network properties of the brain for understanding behavior such as conscious perception. However, with regards to the influence of prestimulus brain states on perception, this network perspective has rarely been taken. Our recent framework predicts that brain regions crucial for a conscious percept are coupled prior to stimulus arrival, forming pre-established pathways of information flow and influencing perceptual awareness. Using magnetoencephalography (MEG) and graph theoretical measures, we investigated auditory conscious perception in a near-threshold (NT) task and found strong support for this framework. Relevant auditory regions showed an increased prestimulus interhemispheric connectivity. The left auditory cortex was characterized by a hub-like behavior and an enhanced integration into the brain functional network prior to perceptual awareness. Right auditory regions were decoupled from non-auditory regions, presumably forming an integrated information processing unit with the left auditory cortex. In addition, we show for the first time for the auditory modality that local excitability, measured by decreased alpha power in the auditory cortex, increases prior to conscious percepts. Importantly, we were able to show that connectivity states seem to be largely independent from local excitability states in the context of a NT paradigm. PMID:26408799

  5. Prestimulus Network Integration of Auditory Cortex Predisposes Near-Threshold Perception Independently of Local Excitability.

    PubMed

    Leske, Sabine; Ruhnau, Philipp; Frey, Julia; Lithari, Chrysa; Müller, Nadia; Hartmann, Thomas; Weisz, Nathan

    2015-12-01

    An ever-increasing number of studies are pointing to the importance of network properties of the brain for understanding behavior such as conscious perception. However, with regards to the influence of prestimulus brain states on perception, this network perspective has rarely been taken. Our recent framework predicts that brain regions crucial for a conscious percept are coupled prior to stimulus arrival, forming pre-established pathways of information flow and influencing perceptual awareness. Using magnetoencephalography (MEG) and graph theoretical measures, we investigated auditory conscious perception in a near-threshold (NT) task and found strong support for this framework. Relevant auditory regions showed an increased prestimulus interhemispheric connectivity. The left auditory cortex was characterized by a hub-like behavior and an enhanced integration into the brain functional network prior to perceptual awareness. Right auditory regions were decoupled from non-auditory regions, presumably forming an integrated information processing unit with the left auditory cortex. In addition, we show for the first time for the auditory modality that local excitability, measured by decreased alpha power in the auditory cortex, increases prior to conscious percepts. Importantly, we were able to show that connectivity states seem to be largely independent from local excitability states in the context of a NT paradigm. PMID:26408799

  6. Recent experiments on near-threshold electron-impact excitation of multiply charged ions

    SciTech Connect

    Bannister, M.E.; Djuric, N.; Woitke, O.; Dunn, G.H. |; Chung, Y.S.; Smith, A.C.H.; Wallbank, B.

    1998-04-01

    Some recent measurements of excitation of multiply charged ions by electrons studied in beam-beam experiments are highlighted. The emphasis is on absolute total cross sections measured with the merged electron-ion beams energy-loss (MEIBEL) technique, although some results obtained with the crossed-beams fluorescence method are also presented. The MEIBEL technique allows the investigation of optically-allowed and forbidden transitions with sufficient energy resolution, typically about 0.2 eV, to resolve resonance structures in the cross sections. Results from the JILA/ORNL MEIBEL experiment on dipole-allowed transitions in several ions demonstrate the success of various theoretical methods in predicting cross sections in the absence of resonances. Comparisons of R-matrix calculations and measured cross sections for spin-forbidden transitions in Mg-like Si{sup 2+} and Ar{sup 6+}, however, show that further refinements to the theory are needed in order to more accurately predict cross sections involving significant contributions from dielectric resonance`s and interactions between neighboring resonances.

  7. Correction of the near threshold behavior of electron collisional excitation cross-sections in the plane-wave Born approximation

    DOE PAGESBeta

    Kilcrease, D. P.; Brookes, S.

    2013-08-19

    The modeling of NLTE plasmas requires the solution of population rate equations to determine the populations of the various atomic levels relevant to a particular problem. The equations require many cross sections for excitation, de-excitation, ionization and recombination. Additionally, a simple and computational fast way to calculate electron collisional excitation cross-sections for ions is by using the plane-wave Born approximation. This is essentially a high-energy approximation and the cross section suffers from the unphysical problem of going to zero near threshold. Various remedies for this problem have been employed with varying degrees of success. We present a correction procedure formore » the Born cross-sections that employs the Elwert–Sommerfeld factor to correct for the use of plane waves instead of Coulomb waves in an attempt to produce a cross-section similar to that from using the more time consuming Coulomb Born approximation. We compare this new approximation with other, often employed correction procedures. Furthermore, we also look at some further modifications to our Born Elwert procedure and its combination with Y.K. Kim's correction of the Coulomb Born approximation for singly charged ions that more accurately approximate convergent close coupling calculations.« less

  8. Correction of the near threshold behavior of electron collisional excitation cross-sections in the plane-wave Born approximation

    SciTech Connect

    Kilcrease, D. P.; Brookes, S.

    2013-08-19

    The modeling of NLTE plasmas requires the solution of population rate equations to determine the populations of the various atomic levels relevant to a particular problem. The equations require many cross sections for excitation, de-excitation, ionization and recombination. Additionally, a simple and computational fast way to calculate electron collisional excitation cross-sections for ions is by using the plane-wave Born approximation. This is essentially a high-energy approximation and the cross section suffers from the unphysical problem of going to zero near threshold. Various remedies for this problem have been employed with varying degrees of success. We present a correction procedure for the Born cross-sections that employs the Elwert–Sommerfeld factor to correct for the use of plane waves instead of Coulomb waves in an attempt to produce a cross-section similar to that from using the more time consuming Coulomb Born approximation. We compare this new approximation with other, often employed correction procedures. Furthermore, we also look at some further modifications to our Born Elwert procedure and its combination with Y.K. Kim's correction of the Coulomb Born approximation for singly charged ions that more accurately approximate convergent close coupling calculations.

  9. Polarization of Lyman-(alpha) Radiation from Atomic Hydrogen Excited by Electron Impact from Near-Threshold to 1800eV

    NASA Technical Reports Server (NTRS)

    James, G. K.; Slevin, J. A.; Dziczek, D.

    1996-01-01

    The polarization of Lyman-(alpha) radiation, produced by electron impact excitation of atomic hydrogen, has been measured for the first time over the extended energy range from near-threshold to 1800eV. Measurements were obtained in a crossed-beams experiment using a silica-reflection linear polarization analyzer in tandem with a vacuum ultraviolet (VUV) monochromator to isolate the emitted line radiation.

  10. 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.

  11. Boltzmann rovibrational collisional coarse-grained model for internal energy excitation and dissociation in hypersonic flows

    NASA Astrophysics Data System (ADS)

    Munafò, A.; Panesi, M.; Magin, T. E.

    2014-02-01

    A Boltzmann rovibrational collisional coarse-grained model is proposed to reduce a detailed kinetic mechanism database developed at NASA Ames Research Center for internal energy transfer and dissociation in N2-N interactions. The coarse-grained model is constructed by lumping the rovibrational energy levels of the N2 molecule into energy bins. The population of the levels within each bin is assumed to follow a Boltzmann distribution at the local translational temperature. Excitation and dissociation rate coefficients for the energy bins are obtained by averaging the elementary rate coefficients. The energy bins are treated as separate species, thus allowing for non-Boltzmann distributions of their populations. The proposed coarse-grained model is applied to the study of nonequilibrium flows behind normal shock waves and within converging-diverging nozzles. In both cases, the flow is assumed inviscid and steady. Computational results are compared with those obtained by direct solution of the master equation for the rovibrational collisional model and a more conventional multitemperature model. It is found that the proposed coarse-grained model is able to accurately resolve the nonequilibrium dynamics of internal energy excitation and dissociation-recombination processes with only 20 energy bins. Furthermore, the proposed coarse-grained model provides a superior description of the nonequilibrium phenomena occurring in shock heated and nozzle flows when compared with the conventional multitemperature models.

  12. Boltzmann rovibrational collisional coarse-grained model for internal energy excitation and dissociation in hypersonic flows.

    PubMed

    Munafò, A; Panesi, M; Magin, T E

    2014-02-01

    A Boltzmann rovibrational collisional coarse-grained model is proposed to reduce a detailed kinetic mechanism database developed at NASA Ames Research Center for internal energy transfer and dissociation in N(2)-N interactions. The coarse-grained model is constructed by lumping the rovibrational energy levels of the N(2) molecule into energy bins. The population of the levels within each bin is assumed to follow a Boltzmann distribution at the local translational temperature. Excitation and dissociation rate coefficients for the energy bins are obtained by averaging the elementary rate coefficients. The energy bins are treated as separate species, thus allowing for non-Boltzmann distributions of their populations. The proposed coarse-grained model is applied to the study of nonequilibrium flows behind normal shock waves and within converging-diverging nozzles. In both cases, the flow is assumed inviscid and steady. Computational results are compared with those obtained by direct solution of the master equation for the rovibrational collisional model and a more conventional multitemperature model. It is found that the proposed coarse-grained model is able to accurately resolve the nonequilibrium dynamics of internal energy excitation and dissociation-recombination processes with only 20 energy bins. Furthermore, the proposed coarse-grained model provides a superior description of the nonequilibrium phenomena occurring in shock heated and nozzle flows when compared with the conventional multitemperature models. PMID:25353565

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

    SciTech Connect

    Song, Lei; Avoird, Ad van der; Karman, Tijs; Groenenboom, Gerrit C.; Balakrishnan, N.

    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. Also 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.

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

    NASA Astrophysics Data System (ADS)

    Song, Lei; Balakrishnan, N.; van der Avoird, Ad; Karman, Tijs; Groenenboom, Gerrit C.

    2015-05-01

    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-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. Also 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.

  15. Rovibrational excitation of H2 and HD due to H: the contribution of reactive scattering

    NASA Astrophysics Data System (ADS)

    Watson Cook, Alexander; Yang, Benhui H.; Stancil, Phillip C.; Forrey, Robert C.; Naduvalath, Balakrishnan

    2016-06-01

    Utilizing the hyperspherical method as implemented in the ABC computational suite of codes (Skouteris et al. 2000), the time-independent Schroedinger equation is solved for the reactive and inelastic scattering probabilities for interactions between hydrogen and its isotopes, particularly H, H2, and HD. A high quality potential energy surface (Miekle et all 2002) was adopted in the scattering Hamiltonian construction. Additionally, we aim to explore uses of GPU-centric computing to increase the efficiency of this method (Baraglia et al.) in order to obtain collisional rate coefficients for the full range of rovibrationally excited H2 and HD, extending the recent study of Lique (2015).Baraglia, R. et al. 2011, in Computational Science and Its ApplicationsLique, F. 2015, MNRAS, 453, 810Mielke, S. L. et al., 2002, J. Chem. Phys., 116, 4142Skouteris, D. et al., 2000, Comp. Phys. Comm., 133, 128The work at UGA is partially support by grant HST-AR-13899.

  16. Ro-vibrational excitation of an organic molecule (HCN) in protoplanetary disks

    NASA Astrophysics Data System (ADS)

    Bruderer, Simon; Harsono, Daniel; van Dishoeck, Ewine F.

    2015-03-01

    Context. Organic molecules are important constituents of protoplanetary disks. Their ro-vibrational lines observed in the near- and mid-infrared are commonly detected toward T Tauri disks. These lines are the only way to probe the chemistry in the inner few au where terrestrial planets form. To understand this chemistry, accurate molecular abundances have to be determined. This is complicated by excitation effects that include radiative pumping. Most analyses so far have made the assumption of local thermal equilibrium (LTE), which may not be fulfilled because of the high gas densities required to collisionally thermalize the vibrational levels of the molecules. Aims: The non-LTE excitation effects of hydrogen cyanide (HCN) are studied to evaluate (i) how the abundance determination is affected by the LTE assumption; (ii) whether the ro-vibrational excitation is dominated by collisions or radiative pumping; and (iii) which regions of protoplanetary disks are traced by certain vibrational bands. Methods: Starting from estimates for the collisional rate coefficients of HCN, non-LTE slab models of the HCN emission were calculated to study the importance of different excitation mechanisms. Using a new radiative transfer model, the HCN emission from a full two-dimensional disk was then modeled to study the effect of the non-LTE excitation, together with the line formation. We ran models tailored to the T Tauri disk AS 205 (N) where HCN lines in both the 3 μm and 14 μm bands have been observed by VLT-CRIRES and the Spitzer Space Telescope. Results: Reproducing the observed 3 μm/14 μm flux ratios requires very high densities and kinetic temperatures (n> 1014 cm-3 and T> 750 K), if only collisional excitation is accounted for. Radiative pumping can, however, excite the lines easily out to considerable radii ~10 au. Consequently, abundances derived from LTE and non-LTE models do not differ by more than a factor of about 3. Models with both a strongly enhanced abundance

  17. Photodissociation of CS and SiO+ from Excited Rovibrational Levels

    NASA Astrophysics Data System (ADS)

    Pattillo, Ryan; Stancil, Phillip C.; McLaughlin, Brendan; McCann, Jim; Forrey, Robert C.; Babb, James

    2016-06-01

    Photodissociation due to ultraviolet (UV) photons is a dominant molecular destruction process in a variety of UV-irradiated interstellar (IS) environments. While most astrochemical models adopt photodissociation rates computed from cross sections out of the molecule's ground rovibrational level (v=0,J=0), they also assume a standard local IS radiation field and opacity due to standard IS dust. However, none of these conditions are satisfied in a host of environments including photodissociation regions, protoplanetary disks, and outflows from AGB stars. To allow for the calculation of reliable photodissociation rates, we compute cross sections from all bound v,J levels of the ground electronic state for two example molecules, CS and SiO+. The cross sections are computed for a large number of excited electronic states using a two-state fully quantum perturbation approach. New ab initio potential energies and transition dipole moment functions, used in the photodissociation calculations, were obtained at the MRCI+Q level of theory using the quantum chemistry package MOLPRO. Applications of the v,J-state-resolved cross sections will be presented as well as LTE photodissociation cross sections which assume a Boltzmann distribution of initial v,J levels.This work is supported at UGA by NASA grant NNX15AI61G.

  18. Photodissociation of CS and SiO from Excited Rovibrational Levels

    NASA Astrophysics Data System (ADS)

    Stancil, P. C.; Pattillo, R. J.; McLaughlin, B. M.; McCann, J. F.; Forrey, R. C.; Babb, J. F.

    2016-05-01

    Photodissociation due to ultraviolet (UV) photons is a dominant molecular destruction process in a variety of UV-irradiated interstellar (IS) environments. While most astrochemical models adopt photodissociation rates computed from cross sections out of the molecule's ground rovibrational level (v = 0 , J = 0), they also assume a standard local IS radiation field and opacity due to standard IS dust. However, none of these conditions are satisfied in a host of environments including photodissociation regions, protoplanetary disks, and outflows from AGB stars. To allow for the calculation of reliable photodissociation rates, we compute cross sections from all bound v , J levels of the ground electronic state for two example molecules, CS and SiO. The cross sections are computed for a large number of excited electronic states using a two-state fully quantum perturbation approach. New ab initio potential energies and transition dipole moment functions, used in the photodissociation calculations, were obtained at the MRCI+Q level of theory using the quantum chemistry package MOLPRO. Applications of the v , J -state-resolved cross sections will be presented as well as LTE photodissociation cross sections which assume a Boltzmann distribution of initial v , J levels. This work is supported at UGA by NASA grant NNX15AI61G.

  19. Variational calculation of highly excited rovibrational energy levels of H2O2.

    PubMed

    Polyansky, Oleg L; Kozin, Igor N; Ovsyannikov, Roman I; Małyszek, Paweł; Koput, Jacek; Tennyson, Jonathan; Yurchenko, Sergei N

    2013-08-15

    Results are presented for highly accurate ab initio variational calculation of the rotation-vibration energy levels of H2O2 in its electronic ground state. These results use a recently computed potential energy surface and the variational nuclear-motion programs WARV4, which uses an exact kinetic energy operator, and TROVE, which uses a numerical expansion for the kinetic energy. The TROVE calculations are performed for levels with high values of rotational excitation, J up to 35. The purely ab initio calculations of the rovibrational energy levels reproduce the observed levels with a standard deviation of about 1 cm(-1), similar to that of the J = 0 calculation, because the discrepancy between theory and experiment for rotational energies within a given vibrational state is substantially determined by the error in the vibrational band origin. Minor adjustments are made to the ab initio equilibrium geometry and to the height of the torsional barrier. Using these and correcting the band origins using the error in J = 0 states lowers the standard deviation of the observed-calculated energies to only 0.002 cm(-1) for levels up to J = 10 and 0.02 cm(-1) for all experimentally known energy levels, which extend up to J = 35. PMID:23611762

  20. Quantum Scattering Study of Ro-Vibrational Excitations in N+N(sub 2) Collisions under Re-entry Conditions

    NASA Technical Reports Server (NTRS)

    Wang, Dunyou; Stallcop, James R.; Dateo, Christopher E.; Schwenke, David W.; Huo, Winifred M.

    2004-01-01

    A three-dimensional time-dependent quantum dynamics approach using a recently developed ab initio potential energy surface is applied to study ro-vibrational excitation in N+N2 exchange scattering for collision energies in the range 2.1- 3.2 eV. State-to-state integral exchange cross sections are examined to determine the distribution of excited rotational states of N(sub 2). The results demonstrate that highly-excited rotational states are produced by exchange scattering and furthermore, that the maximum value of (Delta)j increases rapidly with increasing collision energies. Integral exchange cross sections and exchange rate constants for excitation to the lower (upsilon = 0-3) vibrational energy levels are presented as a function of the collision energy. Excited-vibrational-state distributions for temperatures at 2,000 K and 10,000 K are included.

  1. Rovibrationally Excited Molecules on the Verge of a Triple Breakdown: Molecular and Roaming Mechanisms in the Photodecomposition of Methyl Formate.

    PubMed

    Lombardi, Andrea; Palazzetti, Federico; Aquilanti, Vincenzo; Li, Hou-Kuan; Tsai, Po-Yu; Kasai, Toshio; Lin, King-Chuen

    2016-07-14

    For the photodissociation of the simplest of esters, methyl formate HCOOCH3, the energy threshold for triple fragmentation into H, CH3O, and CO was measured by previous ion-imaging experiments at a sequence of wavelengths. The translational energy features of product CO in the ground vibrational level (υ = 0) and for selected rotational states were characterized. In this integrated experimental and theoretical approach (i) the focus is at a laser energy barely below that threshold; (ii) Fourier-transform infrared emission spectroscopy measurements probe the rovibrational energy deposition in CO(υ) for υ > 0 and the emergence of the roaming phenomenon; (iii) accompanying quantum chemical calculations describe the selective rupture of bonds; and (iv) molecular dynamics simulations of dissociation are performed, introducing an approach explicitly involving outcomes from paths originated nonadiabatically through conical intersections. Quantitative information on energy disposal is provided: we found extensive vibrational excitation of CO, while rotational bands are colder and bimodal, due to contributions from direct and roaming modes. PMID:26898774

  2. Nonlinear theory of kinetic instabilities near threshold

    SciTech Connect

    Berk, H.L.; Pekker, M.S.; Breizman, B.N. |

    1997-05-01

    A new nonlinear equation has been derived and solved for the evolution of an unstable collective mode in a kinetic system close to the threshold of linear instability. The resonant particle response produces the dominant nonlinearity, which can be calculated iteratively in the near-threshold regime as long as the mode doe snot trap resonant particles. With sources and classical relaxation processes included, the theory describes both soft nonlinear regimes, where the mode saturation level is proportional to an increment above threshold, and explosive nonlinear regimes, where the mode grows to a level that is independent of the closeness to threshold. The explosive solutions exhibit mode frequency shifting. For modes that exist in the absence of energetic particles, the frequency shift is both upward and downward. For modes that require energetic particles for their existence, there is a preferred direction of the frequency shift. The frequency shift continues even after the mode traps resonant particles.

  3. Near-threshold electron-impact excitation of the (3p{sup 5}4s4p){sup 4}S{sub /2} quasimetastable state in potassium

    SciTech Connect

    Borovik, A. A. Jr.; Borovik, A. A.; Zatsarinny, O.; Bartschat, K.

    2006-06-15

    Electron-impact excitation of the (3p{sup 5}4s4p){sup 4}S quasimetastable level in potassium has been investigated both experimentally and theoretically for incident energies up to 3 eV above the excitation threshold. The ejected-electron excitation function measured with an energy resolution of 0.25 eV suggests the presence of several strong resonances just above threshold. Satisfactory agreement with the excitation cross section obtained from a sophisticated B-spline R-matrix model with nonorthogonal orbitals supports the importance of K{sup -} resonances predominantly of the (3p{sup 5}4s4p{sup 2}) configuration. Good agreement between theory and experiment is also obtained for the optical excitation function measured earlier with a lower energy resolution of {approx_equal}1.2 eV. The branching ratios for decay of the (3p{sup 5}4s4p){sup 4}S{sub 3/2} level into the electron emission and the optical channels were obtained as 0.16 and 0.69, respectively.

  4. The Cascaded Arc: High Flows of Rovibrationally Excited H{sub 2} and its Impact on H{sup -} Ion Formation

    SciTech Connect

    Gabriel, O.; Harskamp, W. E. N. van; Schram, D. C.; Sanden, M. C. M. van de; Engeln, R.

    2009-03-12

    The cascaded arc is a plasma source providing high fluxes of excited and reactive species such as ions, radicals and rovibrationally excited molecules. The plasma is produced under pressures of some kPa in a direct current arc with electrical powers up to 10 kW. The plasma leaves the arc channel through a nozzle and expands with supersonic velocity into a vacuum-chamber kept by pumps at low pressures. We investigated the case of a pure hydrogen plasma jet with and without an applied axial magnetic field that confines ions and electrons in the jet. Highly excited molecules and atoms were detected by means of laser-induced fluorescence and optical emission spectroscopy. In case of an applied magnetic field the atomic state distribution of hydrogen atoms shows an overpopulation between the electronic states p = 5, 4 and 3. The influence of the highly excited hydrogen molecules on H{sup -} ion formation and a possible mechanism involving this negative ion and producing atomic hydrogen in state p = 3 will be discussed.

  5. Intrashell Electron Interaction Mediated Photoformation of Hollow Atoms near Threshold

    SciTech Connect

    Houtari, S.; Kao, C.; Hamalainen, K.; Diamant, R.; Sharon, R.; Deutsch, M.

    2008-07-25

    Double photoionization (DPI) of an atom by a single photon is a direct consequence of electron-electron interactions within the atom. We have measured the evolution of the K-shell DPI from threshold up in transition metals by high-resolution x-ray emission spectroscopy of the K{sup h}a hypersatellites, photoexcited by monochromatized synchrotron radiation. The measured evolution of the single-to-double photoionization cross-section ratio with excitation energy was found to be universal. Theoretical fits suggest that near threshold DPI is predominantly a semiclassical knockout effect, rather than the purely quantum-mechanical shake-off observed at the infinite photon energy limit.

  6. Absolute cross sections for near-threshold electron-impact excitation of the 2s{sup 2}S{r_arrow}2p{sup 2}P transition in C{sup 3+}

    SciTech Connect

    Bannister, M.E.; Chung, Y.; Djuric, N.; Wallbank, B.; Woitke, O.; Zhou, S.; Dunn, G.H.; Smith, A.C.

    1998-01-01

    Absolute total cross sections for electron-impact excitation of the 2s{sup 2}S{r_arrow}2p{sup 2}P transition in C{sup 3+} were measured from 7.35 eV to 8.45 eV using the merged electron-ion-beams energy-loss technique. The results settle the discrepancy between two previous experiments using the crossed-beams fluorescence method, being in very good agreement with the older results [P. O. Taylor, D. Gregory, G. H. Dunn, R. A. Phaneuf, and D. H. Crandall, Phys. Rev. Lett. {bold 39}, 1256 (1977)] but less so with the more recent ones [D. W. Savin, L. D. Gardner, D. B. Reisenfeld, A. R. Young, and J. L. Kohl, Phys. Rev. A {bold 51}, 2162 (1995)]. The present measurements are also in good agreement with unitarized Coulomb-Born and close-coupling calculations. {copyright} {ital 1998} {ital The American Physical Society}

  7. Absolute cross sections for near-threshold electron-impact excitation of the dipole-allowed transitions 3s2 1S-->3s3p 1P in Cl5+ and 3s 2S-->3p 2P in Cl6+

    NASA Astrophysics Data System (ADS)

    Djurić, N.; Bannister, M. E.; Derkatch, A. M.; Griffin, D. C.; Krause, H. F.; Popović, D. B.; Smith, A. C.; Wallbank, B.; Dunn, G. H.

    2002-05-01

    Experimental and theoretical cross sections for electron-impact excitation of the dipole-allowed transitions 3s2 1S-->3s3p 1P in Cl5+ and 3s 2S-->3p 2P in Cl6+ near the excitation thresholds are reported. Absolute cross sections are measured using the merged electron-ion beams energy-loss technique. The intermediate-coupling frame-transformation R-matrix method is used to obtain theoretical cross sections. The total cross sections, for the transitions studied in both ions, exhibit resonance structures near threshold. There is excellent agreement between theory and experiment with respect to both the shape and the magnitude of the cross section for the 3s 2S-->3p 2P transition in Cl6+. For Cl5+, structures and trends in both the present R-matrix calculation and the previous calculation of Baluja and Mohan [J. Phys. B 20, 831 (1987)] agree well with the experimental results. However, the magnitudes of the theoretical cross sections for Cl5+ are significantly smaller than the measured cross section, which has been corrected for metastable contamination.

  8. Mechanism of near-threshold stimulated desorption of protons from transition-metal surfaces

    SciTech Connect

    Melius, C.F.; Stulen, R.H.; Noell, J.O.

    1982-05-17

    The mechanism for near threshold electron and photon stimulated desorption of protons from transition-metal surfaces has been investigated with use of configuration-interaction techniques on finite clusters. The calculations indicate that the protons arise from repulsive states involving double excitations from the metal-hydrogen bonding orbitals and suggest that the process may occur via a surface predissociation mechanism. The calculations are compared to experimental electron stimulated desorption results for Ni<111>.

  9. Modeling the rovibrationally excited C2H4OH radicals from the photodissociation of 2-bromoethanol at 193 nm.

    PubMed

    Ratliff, B J; Womack, C C; Tang, X N; Landau, W M; Butler, L J; Szpunar, D E

    2010-04-15

    -bromoethanol, our model explicitly includes weighting over geometries across the quantum wave function with zero, one, and two quanta in the harmonic mode that most strongly alters the exit impact parameter. The model gives a nearly perfect prediction of the measured velocity distribution of stable radicals near the dissociation onset using a G4 prediction of the C-Br bond energy and the dissociation barrier for the OH + ethene channel calculated by Senosiain et al. (J. Phys. Chem. A 2006, 110, 6960). The model also indicates that the excited state dissociation proceeds primarily from a conformer of 2-bromoethanol that is trans across the C-C bond. We discuss the possible extensions of our model and the effect of the radical intermediate's J-distribution on the branching between the OH + ethene product channels. PMID:20302318

  10. Mechanism of Anomalous Ellipticity Dependence of Near-threshold Harmonics in H 2 +

    NASA Astrophysics Data System (ADS)

    Nasiri Avanaki, Kobra; Telnov, Dmitry A.; Chu, Shih-I.

    2016-05-01

    We have studied the mechanism of anomalous dependence of near-threshold harmonics in H2+on ellipticity of driving field with the carrier wavelength 780 nm. The numerical procedure is based on accurate solution of the time-dependent Schrödinger equation in prolate spheroidal coordinates with the help of generalized pseudospectral method. Our analysis reveals that the origin of this phenomenon is mainly in the near-resonant excitation of πu molecular orbitals in H2+.For the lowest affected harmonic, the maximum in the ellipticity dependence of the radiation energy is exclusively due to excitation of the 1πu state; however, for higher near-threshold harmonics, higher-lying excited πu states are playing significant role as well. The closer the harmonic to the threshold, the larger number of excited states make considerable contributions. All these contributions interfere, resulting in the anomalous ellipticity dependence with a maximum at some non-zero value of the ellipticity parameter. In the vicinity of this value, the harmonics with the anomalous dependence are linearly polarized along the minor axis of the polarization ellipse of the driving field and may show strong elliptical polarization as well. This work is partially supported by DOE.

  11. Calculating rovibrationally excited states of H2D+ and HD2+ by combination of fixed node and multi-state rotational diffusion Monte Carlo

    NASA Astrophysics Data System (ADS)

    Ford, Jason E.; McCoy, Anne B.

    2016-02-01

    In this work the efficacy of a combined approach for capturing rovibrational coupling is investigated. Specifically, the multi-state rotational DMC method is used in combination with fixed-node DMC in a study of the rotation vibration energy levels of H2D+ and HD2+. Analysis of the results of these calculations shows very good agreement between the calculated energies and previously reported values. Where differences are found, they can be attributed to Coriolis couplings, which are large in these ions and which are not fully accounted for in this approach.

  12. Reexamination of an anomaly in near-threshold pair production

    SciTech Connect

    De Braeckeleer, L.; Adelberger, E.G.; Garcia, A. )

    1992-11-01

    We investigated a reported anomaly in near-threshold pair production, using radioactive sources to measure the {gamma}+Ge{r arrow}{ital e}{sup +}+{ital e}{sup {minus}}+Ge cross-section at {ital E}{sub {gamma}}=1063, 1086, 1112, 1173, 1213, 1299, 1332, and 1408 keV. Although the data agree with the theory (numerical calculations based on an exact partial-wave formulation for a screened central potential) at the higher energies, the data lie above the theory at 1063, 1082, and 1112 keV. The discrepancy is reduced by including the final-state Coulomb interaction between the {ital e}{sup +} and {ital e}{sup {minus}}.

  13. Near-threshold photoproduction of Φ mesons from deuterium

    SciTech Connect

    Qian, X.; Chen, W.; Gao, H.; Hicks, K.; Kramer, K.; Laget, J. M.; Mibe, T.; Qiang, Y.; Stepanyan, S.; Tedeschi, D. J.; Xu, W.; Adhikari, K. P.; Amaryan, M.; Anghinolfi, M.; Ball, J.; Battaglieri, M.; Batourine, V.; Bedlinskiy, I.; Bellis, M.; Biselli, A. S.; Bookwalter, C.; Branford, D.; Briscoe, W. J.; Brooks, W. K.; Burkert, V. D.; Careccia, S. L.; Carman, D. S.; Cole, P. L.; Collins, P.; Crede, V.; D'Angelo, A.; Daniel, A.; Dashyan, N.; De Vita, R.; De Sanctis, E.; Deur, A.; Dey, B.; Dhamija, S.; Djalali, C.; Doughty, D.; Dupre, R.; Egiyan, H.; El Alaoui, A.; Eugenio, P.; Fegan, S.; Gabrielyan, M. Y.; Gevorgyan, N.; Gilfoyle, G. P.; Giovanetti, K. L.; Girod, F. X.; Goetz, J. T.; Gohn, W.; Gothe, R. W.; Graham, L.; Griffioen, K. A.; Guidal, M.; Guo, L.; Hafidi, K.; Hakobyan, H.; Hanretty, C.; Hassall, N.; Holtrop, M.; Ilieva, Y.; Ireland, D. G.; Jawalkar, S. S.; Jo, H. S.; Joo, K.; Keller, D.; Khandaker, M.; Khetarpal, P.; Kim, A.; Kim, W.; Klein, A.; Klein, F. J.; Konczykowski, P.; Kubarovsky, V.; Kuleshov, S. V.; Kuznetsov, V.; Livingston, K.; Martinez, D.; Mayer, M.; McAndrew, J.; McCracken, M. E.; McKinnon, B.; Meyer, C. A.; Mikhailov, K.; Mineeva, T.; Mirazita, M.; Mokeev, V.; Moreno, B.; Moriya, K.; Morrison, B.; Moutarde, H.; Munevar, E.; Nadel-Turonski, P.; Ni, A.; Niccolai, S.; Niculescu, I.; Niroula, M. R.; Osipenko, M.; Ostrovidov, A. I.; Paremuzyan, R.; Park, K.; Park, S.; Pereira, S. Anefalos; Pisano, S.; Pogorelko, O.; Pozdniakov, S.; Price, J. W.; Procureur, S.; Protopopescu, D.; Ricco, G.; Ripani, M.; Ritchie, B. G.; Rosner, G.; Rossi, P.; Sabatié, F.; Saini, M. S.; Salgado, C.; Schott, D.; Schumacher, R. A.; Seder, E.; Seraydaryan, H.; Sharabian, Y. G.; Smith, E. S.; Smith, G. D.; Sober, D. I.; Sokhan, D.; Stepanyan, S. S.; Stoler, P.; Strakovsky, I. I.; Strauch, S.; Taiuti, M.; Taylor, C. E.; Tkachenko, S.; Ungaro, M.; Vernarsky, B.; Vineyard, M. F.; Voutier, E.; Weinstein, L. B.; Weygand, D. P.; Wood, M. H.; Zachariou, N.; Zana, L.; Zhang, J.; Zhao, B.; Zhao, Z. W.

    2011-01-05

    In this report, we measure the differential cross section on $\\phi$-meson photoproduction from deuterium near the production threshold for a proton using the CLAS detector and a tagged-photon beam in Hall B at Jefferson Lab. The measurement was carried out by a triple coincidence detection of a proton, $K^+$ and $K^-$ near the theoretical production threshold of 1.57 GeV. Moreover, the extracted differential cross sections $\\frac{d\\sigma}{dt}$ for the initial photon energy from 1.65-1.75 GeV are consistent with predictions based on a quasifree mechanism. Ultimately, this experiment establishes a baseline for a future experimental search for an exotic $\\phi$-N bound state from heavier nuclear targets utilizing subthreshold/near-threshold production of $\\phi$ mesons.

  14. Near-threshold photoproduction of Φ mesons from deuterium

    DOE PAGESBeta

    Qian, X.; Chen, W.; Gao, H.; Hicks, K.; Kramer, K.; Laget, J. M.; Mibe, T.; Qiang, Y.; Stepanyan, S.; Tedeschi, D. J.; et al

    2011-01-05

    In this report, we measure the differential cross section onmore » $$\\phi$$-meson photoproduction from deuterium near the production threshold for a proton using the CLAS detector and a tagged-photon beam in Hall B at Jefferson Lab. The measurement was carried out by a triple coincidence detection of a proton, $K^+$ and $K^-$ near the theoretical production threshold of 1.57 GeV. Moreover, the extracted differential cross sections $$\\frac{d\\sigma}{dt}$$ for the initial photon energy from 1.65-1.75 GeV are consistent with predictions based on a quasifree mechanism. Ultimately, this experiment establishes a baseline for a future experimental search for an exotic $$\\phi$$-N bound state from heavier nuclear targets utilizing subthreshold/near-threshold production of $$\\phi$$ mesons.« less

  15. Photoproduction of the phi (1020) near threshold in CLAS

    SciTech Connect

    Tedeschi, D J

    2002-06-01

    The differential cross section for the photoproduction of the phi(1020) near threshold (E_{gamma} - 1.57GeV ) is predicted to be sensitive to production mechanisms other than diffraction. However, the existing low energy data is of limited statistics and kinematical coverage. Complete measurements of phi meson production on the proton have been performed at the Thomas Jefferson National Accelerator Facility using a liquid hydrogen target and the CEBAF Large Acceptance Spectrometer (CLAS). The phi was identified by missing mass using a proton and positive kaon detected by CLAS in coincidence with an electron in the photon tagger. The energy of the tagged, bremsstrahlung photons ranged from phi-threshold to 2.4 GeV. A description of the data set and the differential cross section far (E_{gamma} = 2.0 GeV ) will be presented and compared with present theoretical calculations.

  16. Distinguishing near-threshold pole effects from cusp effects

    NASA Astrophysics Data System (ADS)

    Zhou, Zhi-Yong; Xiao, Zhiguang

    2015-11-01

    We make use of a unitarized coupled-channel model to analyze the mass distribution data of final states in production processes of X (4260 ). By analyzing the analytical structures of the decay amplitudes, we find that the line shape of the Zc(3900 ) signal is related to the combined effect of a pair of near-threshold "shadow" poles and the (D D¯*)± thresholds, in which the third-sheet pole might provide a dominant contribution. As all the coupled channels effects are tuning off, the trajectories of these two poles suggest that the Zc(3900 ) might originate from the attractive interaction of (D*D¯*)± through a long-distance interaction, e.g., π -exchange interaction, as a "deuteron-like" state. There is no nearby pole structure corresponding to the Zc(4025 ) signal in the (D*D¯*)± mass distribution.

  17. A Survey of Architectural Techniques for Near-Threshold Computing

    DOE PAGESBeta

    Mittal, Sparsh

    2015-12-28

    Energy efficiency has now become the primary obstacle in scaling the performance of all classes of computing systems. In low-voltage computing and specifically, near-threshold voltage computing (NTC), which involves operating the transistor very close to and yet above its threshold voltage, holds the promise of providing many-fold improvement in energy efficiency. However, use of NTC also presents several challenges such as increased parametric variation, failure rate and performance loss etc. Our paper surveys several re- cent techniques which aim to offset these challenges for fully leveraging the potential of NTC. By classifying these techniques along several dimensions, we also highlightmore » their similarities and differences. Ultimately, we hope that this paper will provide insights into state-of-art NTC techniques to researchers and system-designers and inspire further research in this field.« less

  18. A Survey of Architectural Techniques for Near-Threshold Computing

    SciTech Connect

    Mittal, Sparsh

    2015-12-28

    Energy efficiency has now become the primary obstacle in scaling the performance of all classes of computing systems. In low-voltage computing and specifically, near-threshold voltage computing (NTC), which involves operating the transistor very close to and yet above its threshold voltage, holds the promise of providing many-fold improvement in energy efficiency. However, use of NTC also presents several challenges such as increased parametric variation, failure rate and performance loss etc. Our paper surveys several re- cent techniques which aim to offset these challenges for fully leveraging the potential of NTC. By classifying these techniques along several dimensions, we also highlight their similarities and differences. Ultimately, we hope that this paper will provide insights into state-of-art NTC techniques to researchers and system-designers and inspire further research in this field.

  19. Photoproduction of the ω meson on the proton near threshold

    NASA Astrophysics Data System (ADS)

    Strakovsky, I. I.; Prakhov, S.; Azimov, Ya. I.; Aguar-Bartolomé, P.; Annand, J. R. M.; Arends, H. J.; Bantawa, K.; Beck, R.; Bekrenev, V.; Berghäuser, H.; Braghieri, A.; Briscoe, W. J.; Brudvik, J.; Cherepnya, S.; Codling, R. F. B.; Collicott, C.; Costanza, S.; Demissie, B. T.; Downie, E. J.; Drexler, P.; Fil'kov, L. V.; Glazier, D. I.; Gregor, R.; Hamilton, D. J.; Heid, E.; Hornidge, D.; Jaegle, I.; Jahn, O.; Jude, T. C.; Kashevarov, V. L.; Keshelashvili, I.; Kondratiev, R.; Korolija, M.; Kotulla, M.; Koulbardis, A.; Kruglov, S.; Krusche, B.; Lisin, V.; Livingston, K.; MacGregor, I. J. D.; Maghrbi, Y.; Manley, D. M.; Marinides, Z.; McGeorge, J. C.; McNicoll, E. F.; Mekterovic, D.; Metag, V.; Middleton, D. G.; Mushkarenkov, A.; Nefkens, B. M. K.; Nikolaev, A.; Novotny, R.; Ortega, H.; Ostrick, M.; Otte, P. B.; Oussena, B.; Pedroni, P.; Pheron, F.; Polonski, A.; Robinson, J.; Rosner, G.; Rostomyan, T.; Schumann, S.; Sikora, M. H.; Starostin, A.; Supek, I.; Taragin, M. F.; Tarbert, C. M.; Thiel, M.; Thomas, A.; Unverzagt, M.; Watts, D. P.; Werthmüller, D.; Zehr, F.; A2 Collaboration at MAMI

    2015-04-01

    An experimental study of ω photoproduction on the proton was conducted by using the Crystal Ball and TAPS multiphoton spectrometers together with the photon tagging facility at the Mainz Microtron MAMI. The γ p →ω p differential cross sections are measured from threshold to the incident-photon energy Eγ=1.40 GeV (W =1.87 GeV for the center-of-mass energy) with 15-MeV binning in Eγ and full production-angle coverage. The quality of the present data near threshold gives access to a variety of interesting physics aspects. As an example, an estimation of the ω N scattering length αω p is provided.

  20. NN-->NNπ reaction near threshold in a covariant one-boson-exchange model

    NASA Astrophysics Data System (ADS)

    Shyam, R.; Mosel, U.

    1998-04-01

    We calculate the cross sections for the p(p,nπ+)p and p(p,pπ0)p reactions for proton beam energies near threshold in a covariant one-boson-exchange model, which incorporates the exchange of π, ρ, σ and ω mesons, treats both nucleon and delta isobar as intermediate states. The final state interaction effects are included within the Watson's theory. Within this model the ω and σ meson exchange terms contribute significantly at these energies, which, along with other meson exchanges, make it possible to reproduce the available experimental data for the total as well as differential cross sections for both the reactions. The cross sections at beam energies <=300 MeV are found to be almost free from the contributions of the Δ isobar excitation.

  1. Dynamics of strangeness production in heavy-ion collisions near threshold energies

    SciTech Connect

    Feng Zhaoqing; Jin Genming

    2010-11-15

    Within the framework of the improved isospin-dependent quantum molecular dynamics (ImIQMD) model, the dynamics of strangeness (K{sup 0,+}, {Lambda}, and {Sigma}{sup -,0,+}) production in heavy-ion collisions near threshold energies is investigated systematically, with the strange particles considered to be produced mainly by inelastic collisions of baryon-baryon and pion-baryon. Collisions in the region of suprasaturation densities of the dense baryonic matter formed in heavy-ion collisions dominate the yields of strangeness production. Total multiplicities as functions of incident energies and collision centralities are calculated with the Skyrme parameter SLy6. The excitation function of strangeness production is analyzed and also compared with the KaoS data for K{sup +} production in the reactions {sup 12}C+{sup 12}C and {sup 197}Au+{sup 197}Au.

  2. Detection of Near-Threshold Sounds is Independent of EEG Phase in Common Frequency Bands

    PubMed Central

    Zoefel, Benedikt; Heil, Peter

    2013-01-01

    Low-frequency oscillations in the electroencephalogram (EEG) are thought to reflect periodic excitability changes of large neural networks. Consistent with this notion, detection probability of near-threshold somatosensory, visual, and auditory targets has been reported to co-vary with the phase of oscillations in the EEG. In audition, entrainment of δ-oscillations to the periodic occurrence of sounds has been suggested to function as a mechanism of attentional selection. Here, we examine in humans whether the detection of brief near-threshold sounds in quiet depends on the phase of EEG oscillations. When stimuli were presented at irregular intervals, we did not find a systematic relationship between detection probability and phase. When stimuli were presented at regular intervals (2-s), reaction times were significantly shorter and we observed phase entrainment of EEG oscillations corresponding to the frequency of stimulus presentation (0.5 Hz), revealing an adjustment of the system to the regular stimulation. The amplitude of the entrained oscillation was higher for hits than for misses, suggesting a link between entrainment and stimulus detection. However, detection was independent of phase at frequencies ≥1 Hz. Furthermore, we show that when the data are analyzed using acausal, though common, algorithms, an apparent “entrainment” of the δ-phase to presented stimuli emerges and detection probability appears to depend on δ-phase, similar to reports in the literature. We show that these effects are artifacts from phase distortion at stimulus onset by contamination with the event-related potential, which differs markedly for hits and misses. This highlights the need to carefully deal with this common problem, since otherwise it might bias and mislead this exciting field of research. PMID:23717293

  3. Near-threshold photodetachment of heavy alkali-metal anions

    SciTech Connect

    Bahrim, C.; Thumm, U.; Khuskivadze, A.A.; Fabrikant, I.I.

    2002-11-01

    We calculate near-threshold photodetachment cross sections for Rb{sup -}, Cs{sup -}, and Fr{sup -} using the Pauli equation method with a model potential describing the effective electron-atom interaction. Parameters of the model potential are fitted to reproduce ab initio scattering phase shifts obtained from Dirac R-matrix calculations. Special care is taken to formulate the boundary conditions near the atomic nucleus for solving the Pauli equation, based on the analytic solution of the Dirac equation for a Coulomb potential. We find a {sup 3}P{sub 1}{sup o} resonance contribution to the photodetachment cross section of Rb{sup -}, Cs{sup -}, and Fr{sup -} ions. Our calculated total photodetachment cross sections for Cs agree with experiments after tuning the resonance position by 2.4 meV. For Rb{sup -} and Fr{sup -} the resonance contribution is much smaller than for Cs. We therefore also provide angle-differential cross sections and asymmetry parameters which are much more sensitive to the resonant contribution than total cross sections.

  4. Near-Threshold, Vibrationally-Resolved Photoionization of Molecular Nitrogen

    NASA Astrophysics Data System (ADS)

    Vangyseghem, Gaetan; Gorczyca, Thomas; Ballance, Connor

    2016-05-01

    Photoionization of molecular nitrogen N2 is investigated near the first ionization threshold using an R-matrix, multi-channel quantum defect theory (MQDT) approach. Building on an existing fixed-nuclei R-matrix photoionization model, which, in turn, is built on the UKRmol suite of codes, photoionization cross sections, as well as scattering and dipole matrices, are computed in the Born-Oppenheimer approximation. By varying the internuclear separation, potential energy curves have been constructed for the N2 and N 2 + states and compared to quantum chemistry calculations. Using these fixed-nuclei potential energy curves, and corresponding vibronic eigenenergies and eigenfunctions, a frame transformation is enacted on the fixed-nuclei scattering and dipole matrices, allowing for the calculation of vibrationally-resolved photoionization cross sections. The resultant photoionization cross sections are compared to high-resolution experimental data near threshold, a region complicated by multiple vibrationally-resolved, interacting Rydberg series.

  5. Accurate calculations of bound rovibrational states for argon trimer

    SciTech Connect

    Brandon, Drew; Poirier, Bill

    2014-07-21

    This work presents a comprehensive quantum dynamics calculation of the bound rovibrational eigenstates of argon trimer (Ar{sub 3}), using the ScalIT suite of parallel codes. The Ar{sub 3} rovibrational energy levels are computed to a very high level of accuracy (10{sup −3} cm{sup −1} or better), and up to the highest rotational and vibrational excitations for which bound states exist. For many of these rovibrational states, wavefunctions are also computed. Rare gas clusters such as Ar{sub 3} are interesting because the interatomic interactions manifest through long-range van der Waals forces, rather than through covalent chemical bonding. As a consequence, they exhibit strong Coriolis coupling between the rotational and vibrational degrees of freedom, as well as highly delocalized states, all of which renders accurate quantum dynamical calculation difficult. Moreover, with its (comparatively) deep potential well and heavy masses, Ar{sub 3} is an especially challenging rare gas trimer case. There are a great many rovibrational eigenstates to compute, and a very high density of states. Consequently, very few previous rovibrational state calculations for Ar{sub 3} may be found in the current literature—and only for the lowest-lying rotational excitations.

  6. Accurate calculations of bound rovibrational states for argon trimer.

    PubMed

    Brandon, Drew; Poirier, Bill

    2014-07-21

    This work presents a comprehensive quantum dynamics calculation of the bound rovibrational eigenstates of argon trimer (Ar3), using the ScalIT suite of parallel codes. The Ar3 rovibrational energy levels are computed to a very high level of accuracy (10(-3) cm(-1) or better), and up to the highest rotational and vibrational excitations for which bound states exist. For many of these rovibrational states, wavefunctions are also computed. Rare gas clusters such as Ar3 are interesting because the interatomic interactions manifest through long-range van der Waals forces, rather than through covalent chemical bonding. As a consequence, they exhibit strong Coriolis coupling between the rotational and vibrational degrees of freedom, as well as highly delocalized states, all of which renders accurate quantum dynamical calculation difficult. Moreover, with its (comparatively) deep potential well and heavy masses, Ar3 is an especially challenging rare gas trimer case. There are a great many rovibrational eigenstates to compute, and a very high density of states. Consequently, very few previous rovibrational state calculations for Ar3 may be found in the current literature-and only for the lowest-lying rotational excitations. PMID:25053315

  7. Rovibrationally resolved photodissociation of SH+

    NASA Astrophysics Data System (ADS)

    McMillan, E. C.; Shen, G.; McCann, J. F.; McLaughlin, B. M.; Stancil, P. C.

    2016-04-01

    Photodissociation cross sections for the SH+ radical are computed from all rovibrational (RV) levels of the ground electronic state {{X}}{}3{{{Σ }}}- for wavelengths from threshold to 500 Å. The five electronic transitions, 2{}3{{{Σ }}}- ≤ftarrow {{X}}{}3{{{Σ }}}-,3{}3{{{Σ }}}- ≤ftarrow {{X}}{}3{{{Σ }}}-, A{}3{{\\Pi }} ≤ftarrow {{X}}{}3{{{Σ }}}-,2{}3{{\\Pi }} ≤ftarrow {{X}}{}3{{{Σ }}}-, and 3{}3{{\\Pi }} ≤ftarrow {{X}}{}3{{{Σ }}}-, are treated with a fully quantum–mechanical two-state model, i.e. nonadiabatic couplings between excited states were not included. The photodissociation calculations incorporate adiabatic potentials and transition dipole moment functions computed in the multireference configuration interaction approach along with the Davidson correction (MRCI+Q), but adjusted to match available experimental molecular data and asymptotic atomic limits. Local thermodynamic equilibrium (LTE) photodissociation cross sections were computed which assume a Boltzmann distribution of RV levels in the {{X}}{}3{{{Σ }}}- molecular state of the SH+ cation. The LTE cross sections are presented for temperatures in the range 1000–10 000 K. Applications of the current photodissociation cross sections to interstellar gas, photon-dominated regions, and stellar atmospheres are briefly discussed.

  8. Accelerated Near-Threshold Fatigue Crack Growth Behavior of an Aluminum Powder Metallurgy Alloy

    NASA Technical Reports Server (NTRS)

    Piascik, Robert S.; Newman, John A.

    2002-01-01

    Fatigue crack growth (FCG) research conducted in the near threshold regime has identified a room temperature creep crack growth damage mechanism for a fine grain powder metallurgy (PM) aluminum alloy (8009). At very low DK, an abrupt acceleration in room temperature FCG rate occurs at high stress ratio (R = Kmin/Kmax). The near threshold accelerated FCG rates are exacerbated by increased levels of Kmax (Kmax less than 0.4 KIC). Detailed fractographic analysis correlates accelerated FCG with the formation of crack-tip process zone micro-void damage. Experimental results show that the near threshold and Kmax influenced accelerated crack growth is time and temperature dependent.

  9. Critical nonlinear phenomena for kinetic instabilities near threshold

    SciTech Connect

    Breizman, B.N.; Berk, H.L.; Pekker, M.S.; Porcelli, F.; Stupakov, G.V.; Wong, K.L.

    1996-12-01

    A universal integral equation has been derived and solved for the nonlinear evolution of collective modes driven by kinetic wave particle resonances just above the threshold for instability. The dominant nonlinearity stems from the dynamics of resonant particles which can be treated perturbatively near the marginal state of the system. With a resonant particle source and classical relaxation processes included, the new equation allows the determination of conditions for a soft nonlinear regime, where the saturation level is proportional to the increment above threshold, or a hard nonlinear regime, where the saturation level is independent of the closeness to threshold. It has been found, both analytically and numerically, that in the hard regime the system exhibits explosive behavior and rapid oscillations of the mode amplitude. When the kinetic response is a requirement for the existence of the mode, this explosive behavior is accompanied by frequency chirping. The universality of the approach suggests that the theory applies to many types of resonant particle driven instabilities, and several specific cases, viz. energetic particle driven Alfven wave excitation, the fishbone oscillation, and a collective mode in particle accelerators, are discussed.

  10. Near-threshold Ps(n=2)-p scattering

    NASA Astrophysics Data System (ADS)

    Fabrikant, Ilya; Bray, Igor

    2016-05-01

    We study the threshold behavior of elastic and inelastic collisions of the excited positronium (Ps) atom with the proton using the theory developed by Gailitis. We show that partial cross sections for elastic and quasielastic processes exhibit pronounced oscillations above the threshold and diverge as 1 / E where E is the collision energy. This behavior is limited from below by the energy equal to the relativistic splitting between degenerate Ps states. Ab initio close coupling calculations are in excellent agreement with the results of the threshold theory. The oscillations almost completely disappear in the total (summed over partial waves) cross sections. However, dipole-supported resonances appear in inelastic processes, in particular in the important process Ps(nl) + p --> H(n'l') +e+ below higher-energy thresholds. Above thresholds these cross sections don't exhibit oscillations but have the 1 / E divergence in an exothermic case. These results are important for current attempts to produce antihydrogen in a similar charge-conjugated reaction Ps(nl) + p --> H (n'l') +e- . Supported by the US National Science Foundation.

  11. Near-threshold electron-impact doubly differential cross sections for the ionization of argon and krypton

    SciTech Connect

    Yates, Brent R.; Khakoo, Murtadha A.

    2011-04-15

    We present normalized doubly differential cross sections (DDCS's) for the near-threshold, electron-impact single ionization of argon and krypton, similar to those taken earlier for Ne and Xe [Yates et al., J. Phys. B 42, 095206 (2009)]. The Ar measurements were taken at incident energies of 17, 18, 20, and 30 eV while the Kr measurements were taken at 15, 16, 17.5, and 20 eV. The DDCS scattering angles range from 15 deg. to 120 deg. The differential data are initially normalized to available experimental cross sections for excitation of the ground np{sup 6} to the np{sup 5}(n+1)s excited states of the noble gas and, after integration, to well-established experimental total ionization cross sections of Rapp and Englander-Golden [J. Chem. Phys. 43, 1464 (1965)].

  12. Exploration of the origin of anomalous dependence for near-threshold harmonics in {{\\rm{H}}}_{2}^{+} on the ellipticity of driving laser fields

    NASA Astrophysics Data System (ADS)

    Nasiri Avanaki, K.; Telnov, Dmitry A.; Chu, Shih-I.

    2016-06-01

    The anomalous dependence of near-threshold harmonics in the {{{H}}}2+ molecular ion on the ellipticity of the driving near-infrared laser field is studied theoretically based on accurate solution of the time-dependent Schrödinger equation in prolate spheroidal coordinates with the help of the generalized pseudospectral method. For these harmonics, the maximum radiation energy corresponds to a non-zero ellipticity of the driving field. Our analysis reveals that the origin of the phenomenon lies in the near-resonant excitation of π-symmetry molecular orbitals. The excited states responsible for the anomalous ellipticity dependence of different near-threshold harmonics are identified. The effect is confirmed at the equilibrium internuclear separation R = 2 a.u. as well as for stretched molecules at R = 3 a.u.

  13. A Near-Threshold Shape Resonance in the Valence-Shell Photoabsorption of Linear Alkynes.

    PubMed

    Jacovella, U; Holland, D M P; Boyé-Péronne, S; Gans, Bérenger; de Oliveira, N; Ito, K; Joyeux, D; Archer, L E; Lucchese, R R; Xu, Hong; Pratt, S T

    2015-12-17

    The room-temperature photoabsorption spectra of a number of linear alkynes with internal triple bonds (e.g., 2-butyne, 2-pentyne, and 2- and 3-hexyne) show similar resonances just above the lowest ionization threshold of the neutral molecules. These features result in a substantial enhancement of the photoabsorption cross sections relative to the cross sections of alkynes with terminal triple bonds (e.g., propyne, 1-butyne, 1-pentyne, ...). Based on earlier work on 2-butyne [ Xu et al., J. Chem. Phys. 2012, 136, 154303 ], these features are assigned to excitation from the neutral highest occupied molecular orbital (HOMO) to a shape resonance with g (l = 4) character and approximate π symmetry. This generic behavior results from the similarity of the HOMOs in all internal alkynes, as well as the similarity of the corresponding gπ virtual orbital in the continuum. Theoretical calculations of the absorption spectrum above the ionization threshold for the 2- and 3-alkynes show the presence of a shape resonance when the coupling between the two degenerate or nearly degenerate π channels is included, with a dominant contribution from l = 4. These calculations thus confirm the qualitative arguments for the importance of the l = 4 continuum near threshold for internal alkynes, which should also apply to other linear internal alkynes and alkynyl radicals. The 1-alkynes do not have such high partial waves present in the shape resonance. The lower l partial waves in these systems are consistent with the broader features observed in the corresponding spectra. PMID:26469080

  14. Combined analysis of the K+K- interaction using near-threshold pp→ppK+K- data

    NASA Astrophysics Data System (ADS)

    Silarski, M.; Moskal, P.

    2013-08-01

    The K+K- final state interaction was investigated based on both the K+K- invariant mass distributions measured at excess energies of Q=10 and 28 MeV and the near threshold excitation function for the pp→ppK+K- reaction. The K+K- final state enhancement factor was parametrized using the effective range expansion. The effective range of the K+K- interaction was estimated to be Re(bK+K-)=-0.1±0.4stat±0.3sysfm and Im(bK+K-)=1.2-0.2stat-0.0sys+0.1stat+0.2sysfm, and the determined real and imaginary parts of the K+K- scattering length amount to Re(aK+K-)=8.0-4.0stat+6.0statfm and Im(aK+K-)=0.0-5.0stat+20.0statfm.

  15. Unimolecular dissociation of CH 3SH + near threshold: A theoretical study

    NASA Astrophysics Data System (ADS)

    Choe, Joong Chul

    2006-04-01

    The unimolecular dissociation of methanethiol cation (CH 3SH +, 1) has been investigated theoretically. Ab initio and Gaussian-2 theory calculations have been performed to obtain the potential energy surface (PES) for loss of H and H 2 from 1. On the basis of the PES obtained, the relative abundances of the two channels near threshold have been calculated by Rice-Ramsperger-Kassel-Marcus modeling. The calculated result agrees with the previous experimental one, suggesting that the dissociation occurs statistically near threshold on the ground electronic state.

  16. Satellite Band in the Rovibrational Spectrum of CO{sub 2} in Helium Droplets

    SciTech Connect

    Hoshina, Hiromichi; Slipchenko, Mikhail N.; Kuyanov, Kirill E.; Vilesov, Andrey F.; Lucrezi, Jacob

    2005-05-20

    Pulsed infrared ({nu}{approx_equal}2350 cm{sup -1}) laser excitation spectra of CO{sub 2} molecules embedded in helium droplets are reported. The spectra exhibit a sharp R(0) rovibrational line accompanied by a weak broader ({delta}{nu}{approx_equal}10 cm{sup -1}) satellite band, which is shifted by 14 cm{sup -1} towards higher frequencies. We assign this satellite band to a simultaneous rovibrational excitation of a molecule and its helium solvation shell. The results are rationalized within a model, which includes coupling of the rotational states of a molecule and a ring of He atoms.

  17. Rotational And Rovibrational Energy Transfer In Electron Collisions With Molecules

    NASA Technical Reports Server (NTRS)

    Thuemmel, Helmar T.; Langhoff, Stephen R. (Technical Monitor)

    1995-01-01

    Air flows around a hypervelocity reentry vehicle undergo dissociation, rovibrational excitation and ionization. More specifically the air, initially 80% N2 and 20% O2, in the shock layer consists of species such as N, O, N2, O2, NO, N+, O+, N+, O+, NO+ and 2 free electrons. It was pointed out in multi temperature models'' that the temperature of the rotational energy modes and the gas-kinetic translational temperature are quickly equilibrated by a few collisions and rise rapidly to high temperatures as 50000K before falling off to equilibrium value of 10000K. Contrary, the electronic and vibrational temperatures state energy distributions remain low (less than 15000K) because of the slow equilibration. Electron vibrational energy transfer is thought to play a crucial role in such a ionizing flow regime since chemical reaction rates and dissociation depend strongly on the vibrational temperatures. Modeling of these flowfields in principle require the rovibrational excitation and de-excitation cross section data for average electron energies from threshold up to several eV (leV=11605.4 K). In this lecture we focus on theoretical description of rotational effects i.e. energy transfer of electrons to molecules such that the molecular rotational (vojo goes to voj) or vibrational and rotational (v(sub 0)j(sub 0) goes to vj) states are changed. Excitation and de-excitation of electronic states was discussed in a previous talk at this conference.

  18. Near threshold enhancement of the p p-bar mass spectrum in J/Psi decay

    SciTech Connect

    A. Sibirtsev; J. Haidenbauer; S. Krewald; Ulf-G. Meissner; A.W. Thomas

    2004-12-01

    We investigate the nature of the near-threshold enhancement in the p {bar p} invariant mass spectrum of the reaction J/{Psi} {yields} {gamma} p {bar p} reported recently by the BES Collaboration. Using the Juelich N {bar N} model we show that the mass dependence of the p {bar p} spectrum close to the threshold can be reproduced by the S-wave p {bar p} final state interaction in the isospin I=1 state within the Watson-Migdal approach. However, because of our poor knowledge of the N {bar N} interaction near threshold and of the J/{Psi} {yields} {gamma} p {bar p} reaction mechanism and in view of the controversial situation in the decay J/{Psi} {yields} {pi}{sup 0} p {bar p}, where no obvious signs of a p {bar p} final state interaction are seen, explanations other than final state interactions cannot be ruled out at the present stage.

  19. New method to evaluate the 7Li(p, n)7Be reaction near threshold

    NASA Astrophysics Data System (ADS)

    Herrera, María S.; Moreno, Gustavo A.; Kreiner, Andrés J.

    2015-04-01

    In this work a complete description of the 7Li(p, n)7Be reaction near threshold is given using center-of-mass and relative coordinates. It is shown that this standard approach, not used before in this context, leads to a simple mathematical representation which gives easy access to all relevant quantities in the reaction and allows a precise numerical implementation. It also allows in a simple way to include proton beam-energy spread affects. The method, implemented as a C++ code, was validated both with numerical and experimental data finding a good agreement. This tool is also used here to analyze scattered published measurements such as (p, n) cross sections, differential and total neutron yields for thick targets. Using these data we derive a consistent set of parameters to evaluate neutron production near threshold. Sensitivity of the results to data uncertainty and the possibility of incorporating new measurements are also discussed.

  20. Resonances in near-threshold x-ray photoabsorption of inner shells

    SciTech Connect

    Del Grande, N.K.; Tirsell, K.G.; Schneider, M.B.; Garrett, R.F.; Kneedler, E.M.; Manson, S.T.

    1987-08-24

    Synchrotron radiation measurements of near-threshold and broad-range (20 eV - 3 keV) absolute photoabsorption cross sections were made at the Brookhaven National Laboratory (NSLS) and at Stanford (SSRL). Transmission data for well-characterized multilayer foils provided absolute cross sections with 10% overall uncertainties and better than 0.2% energy resolution. Several examples of our results are presented.

  1. Near-threshold boson pair production in the model of smeared-mass unstable particles

    SciTech Connect

    Kuksa, V. I.; Pasechnik, R. S.

    2010-09-15

    Near-threshold production of boson pairs is considered within the framework of the model of unstable particles with smeared mass. We describe the principal aspects of the model and consider the strategy of calculations including the radiative corrections. The results of calculations are in good agreement with LEP II data and Monte-Carlo simulations. Suggested approach significantly simplifies calculations with respect to the standard perturbative one.

  2. Near-threshold photoelectron spectrum in resonant two-photon ionization of atoms

    SciTech Connect

    Raczyn-acute-accentski, A.; Zaremba, J.

    1987-11-15

    The near-threshold photoelectron spectrum in a resonant two-photon ionization process is investigated using a nonperturbative method. The hydrogen atom is represented by a realistic model including an infinite number of Rydberg states converging at the threshold. When the threshold is crossed a typical two-peak structure of the spectrum is modified by cutting off part of the spectrum which may include one or even two peaks.

  3. Analyses of Fatigue Crack Growth and Closure Near Threshold Conditions for Large-Crack Behavior

    NASA Technical Reports Server (NTRS)

    Newman, J. C., Jr.

    1999-01-01

    A plasticity-induced crack-closure model was used to study fatigue crack growth and closure in thin 2024-T3 aluminum alloy under constant-R and constant-K(sub max) threshold testing procedures. Two methods of calculating crack-opening stresses were compared. One method was based on a contact-K analyses and the other on crack-opening-displacement (COD) analyses. These methods gave nearly identical results under constant-amplitude loading, but under threshold simulations the contact-K analyses gave lower opening stresses than the contact COD method. Crack-growth predictions tend to support the use of contact-K analyses. Crack-growth simulations showed that remote closure can cause a rapid rise in opening stresses in the near threshold regime for low-constraint and high applied stress levels. Under low applied stress levels and high constraint, a rise in opening stresses was not observed near threshold conditions. But crack-tip-opening displacement (CTOD) were of the order of measured oxide thicknesses in the 2024 alloy under constant-R simulations. In contrast, under constant-K(sub max) testing the CTOD near threshold conditions were an order-of-magnitude larger than measured oxide thicknesses. Residual-plastic deformations under both constant-R and constant-K(sub max) threshold simulations were several times larger than the expected oxide thicknesses. Thus, residual-plastic deformations, in addition to oxide and roughness, play an integral part in threshold development.

  4. Analytical and Experimental Study of Near-Threshold Interactions Between Crack Closure Mechanisms

    NASA Technical Reports Server (NTRS)

    Newman, John A.; Riddell, William T.; Piascik, Robert S.

    2003-01-01

    The results of an analytical closure model that considers contributions and interactions between plasticity-, roughness-, and oxide-induced crack closure mechanisms are presented and compared with experimental data. The analytical model is shown to provide a good description of the combined influences of crack roughness, oxide debris, and plasticity in the near-threshold regime. Furthermore, analytical results indicate that closure mechanisms interact in a non-linear manner such that the total amount of closure is not the sum of closure contributions for each mechanism.

  5. Morphological study of near threshold fatigue crack growth in a coarse grain aluminum alloy

    NASA Technical Reports Server (NTRS)

    Maurer, Gerhard; Liu, H. W.

    1984-01-01

    Fatigue crack propagation in the near-threshold region has been studied in coarse grain Al 7029 alloy. Over eighty percent of the crack surfaces are planar areas parallel to either 100-oriented or 111-oriented planes. The 100-plane crack surfaces show 'pine tree' morphological features formed by slip on two sets of intersecting planes. The 111-plane crack surfaces were planar and shiny. They were formed primarily by slip on a single dominant 111-oriented slip plane with sparse and very light secondary slip markings. Crack growth rates were measured and correlated with Delta-K.

  6. Calculation of fully differential cross sections for the near threshold double ionization of helium atoms

    NASA Astrophysics Data System (ADS)

    Singh, Prithvi; Purohit, Ghanshyam; Dorn, Alexander; Ren, Xueguang; Patidar, Vinod

    2016-01-01

    Fully differential cross sectional (FDCS) results are reported for the electron-impact double ionization of helium atoms at 5 and 27 eV excess energy. The present attempt to calculate the FDCS in the second Born approximation and treating the postcollision interaction is helpful to analyze the measurements of Ren et al (2008 Phys. Rev. Lett. 101 093201) and Durr et al (2007 Phys. Rev. Lett. 98 193201). The second-order processes and postcollision interaction have been found to be significant in describing the trends of the FDCS. More theoretical effort is required to describe the collision dynamics of electron-impact double ionization of helium atoms at near threshold.

  7. Near-Threshold Fatigue Crack Growth Behavior of Fine-Grain Nickel-Based Alloys

    NASA Technical Reports Server (NTRS)

    Newman, John A.; Piascik, Robert S.

    2003-01-01

    Constant-Kmax fatigue crack growth tests were performed on two finegrain nickel-base alloys Inconel 718 (DA) and Ren 95 to determine if these alloys exhibit near-threshold time-dependent crack growth behavior observed for fine-grain aluminum alloys in room-temperature laboratory air. Test results showed that increases in K(sub max) values resulted in increased crack growth rates, but no evidence of time-dependent crack growth was observed for either nickel-base alloy at room temperature.

  8. Lattice study of (D¯ 1D*)± near-threshold scattering

    NASA Astrophysics Data System (ADS)

    Chen, Ting; Chen, Ying; Gong, Ming; Lei, Yu-Hong; Li, Ning; Liu, Chuan; Liu, Yu-Bin; Liu, Zhao-Feng; Ma, Jian-Ping; Wang, Zhan-Lin; Zhang, Jian-Bo; Clqcd Collaboration

    2016-06-01

    In this exploratory lattice study, low-energy near threshold scattering of the (D¯1D*)± meson system is analyzed using lattice QCD with Nf=2 twisted mass fermion configurations. Both s-wave (JP=0-) and p-wave (JP=1+) channels are investigated. It is found that the interaction between the two charmed mesons is attractive near the threshold in both channels. This calculation provides some hints in the searching of resonances or bound states around the threshold of (D¯1D*)± system.

  9. Angular distributions in J/{psi}({rho}{sup 0},{omega}) states near threshold

    SciTech Connect

    Rosner, Jonathan L.

    2004-11-01

    A resonance X(3872), first observed in the decays B{yields}KX, has been seen to decay to J/{psi}{pi}{sup +}{pi}{sup -}. The {pi}{sup +}{pi}{sup -} mass spectrum peaks near its kinematic upper limit, prompting speculation that the dipion system may be in a {rho}{sup 0}. The decay X(3872){yields}J/{psi}{omega} also has been observed. The reaction {gamma}{gamma}{yields}J/{psi}{pi}{sup +}{pi}{sup -} has been studied. Consequently, angular distributions in decays of J/{psi}({rho}{sup 0},{omega}) states near threshold are of interest, and results are presented.

  10. Influence of gaseous environments on rates of near-threshold fatigue crack propagation in nicrmov steel

    NASA Astrophysics Data System (ADS)

    Liaw, Peter K.; Hudak, S. J.; Donald, J. Keith

    1982-09-01

    The influence of hydrogen environment (448 kPa) on near-threshold fatigue crack propagation rates was examined in a 779 MPa yield strength NiCrMoV steel at 93 °C. An automatically decreasing and increasing stress intensity technique was employed to generate crack growth rates at three load ratios (R = 0.1, 0.5, and 0.8). Results show that the crack propagation rates in hydrogen are slower than those in air for levels of stress intensity range, ΔK, below about 12 MPa√m. The crack closure concept does not explain the slower crack growth rates in hydrogen than in air. Near-threshold growth rates appear to be controlled by the levels of residual moisture in the environments. In argon and air, the fracture morphology is transgranular, while in H2 the amount of intergranularity varies with ΔK and achieves a maximum when the cyclic plastic zone is approximately equal to the prior austenite grain size.

  11. OBSERVATION OF pbar {p}, pbar {Λ }, K-bar {Λ } NEAR-THRESHOLD ENHANCEMENT AT BES

    NASA Astrophysics Data System (ADS)

    Yang, Hongxun

    We observe a narrow enhancement near 2mp in the invariant mass spectrum of pbar {p} pairs from radiative J/ψ -> γ pbar {p} decays. In the case of S-wave fit, the peak mass is below 2mp at M=1859+3-10(stat)+5-25(syst)MeV and the total width is Γ<30MeV at the 90% confidence level. And we also find near-threshold enhancement in the invariant mass spectrum of pbar {Λ }+c.c. in J/ψ -> p K- bar {Λ }+c.c. decays. The mass is m=2075±12(stat)±5(syst)MeV and width is Γ=90±35(stat)±9(syst)MeV. A K- bar {Λ } near-threshold enhancement is also studied and it has m=1.50 1.65GeV, Γ=70 110MeV with BR(J/ψ -> pNX*) × BR(NX* -> KΛ ) ˜ 2 × 10-4.

  12. A resonance interpretation for the nonmonotonic behavior of the φ photoproduction cross section near threshold

    NASA Astrophysics Data System (ADS)

    Nan Yang, Shin; Kiswandhi, Alvin; Xie, Ju-Jun

    2011-10-01

    We study whether the nonmonotonic behavior found in the differential cross section of the φ-meson photoproduction near threshold can be described by a resonance. The resonant contribution is evaluated by using an effective Lagrangian approach. We find that, with the assumption of a JP = 3/2- resonance with mass of 2.10±0.03 GeV and width of 0.465±0.141 GeV, LEPS data can indeed be well described. The ratio of the helicity amplitudes A1/2/A3/2 calculated from the re-22 sulting coupling constants differs in sign from that of the known D13(2080). We further find that the addition of this postulated resonance can substantially improve the agreement between the existing theoretical predictions and the recent ω photoproduction data if a large value of the OZI evading parameter xOZI = 12 is assumed for the resonance.

  13. Study of Near-Threshold Fatigue Crack Propagation in Pipeline Steels in High Pressure Environments

    NASA Technical Reports Server (NTRS)

    Mitchell, M.

    1981-01-01

    Near threshold fatigue crack propagation in pipeline steels in high pressure environments was studied. The objective was to determine the level of threshold stress intensity for fatigue crack growth rate behavior in a high strength low alloy X60 pipeline-type steel. Complete results have been generated for gaseous hydrogen at ambient pressure, laboratory air at ambient pressure and approximately 60% relative humidity as well as vacuum of 0.000067 Pa ( 0.0000005 torr) at R-ratios = K(min)/K(max) of 0.1, 0.5, and 0.8. Fatigue crack growth rate behavior in gaseous hydrogen, methane, and methane plus 10 percent hydrogen at 6.89 MPa (100 psi) was determined.

  14. Finite-Width Effects in the Near-Threshold Zzz and Zww Production at Ilc

    NASA Astrophysics Data System (ADS)

    Pasechnik, Roman; Kuksa, Vladimir

    We calculate the cross-section of the near-threshold off-shell ZZZ and ZW+W- production at the International Linear Collider taking into account their instability and the principal part of next-to-leading order corrections. The calculations are performed in the framework of the model of unstable particles with smeared mass-shell. We show that the contribution of the finite Z/W and H widths (their instability) is large in the Higgs resonance range (about -24% and -18% for ZZZ and ZW+W-, respectively, at √ {s} = 300 GeV) and should be taken into account in the Higgs boson studies at the future International Linear Collider.

  15. Photon scattering on /sup 238/U and the interpretation of near-threshold photofission resonances

    SciTech Connect

    Birenbaum, Y.; Alarcon, R.; Hoblit, S.D.; Laszewski, R.M.; Nathan, A.M.

    1987-10-01

    Cross sections for photon elastic scattering have been measured for /sup 238/U between 4.8 and 6.4 MeV with an energy resolution of about 50 keV. These data have been used along with existing photofission data to infer the total photoabsorption cross section sigma/sub T/ and the fission transmission coefficient T/sub f/ below neutron threshold. We find that the inferred sigma/sub T/ varies smoothly with energy and generally follows the extrapolated tail of the giant dipole resonance, and that T/sub f/ shows a broad bump between 5.6 and 5.9 MeV. These results strongly support the contention that resonances seen in near-threshold photofission cross sections are due to the fission and not the photon channel .

  16. Radiative and rovibrational collisional relaxation of sodium dimer

    NASA Astrophysics Data System (ADS)

    Bayram, Burcin; Horton, Tim; McFarland, Jacob

    2016-05-01

    Radiative and rovibrational collisional relaxation of sodium dimer of the A1Σu+ (8,30) state have been measured by direct observation of the decay fluorescence. Sodium molecular vapor is created in a heatpipe oven at 600 K and excited using a 6-ns pulsed dye laser pumped by a Nd:YAG, operating at 532 nm. The preliminary lifetime measurement was done by directly acquiring lifetime data through boxcar averager from the stored oscilloscope trace of the fluorescence. Analysis of the exponential decay of the fluorescence allows us to obtain the radiative lifetime. By introducing the argon buffer gas and varying the pressure of the heatpipe, a collisional cross section between excited sodium dimer and ground state argon atom collision can be extracted using Stern-Volmer relation.

  17. Identifying the structure of near-threshold states from the line shape

    NASA Astrophysics Data System (ADS)

    Chen, Guo-Ying; Huo, Wen-Sheng; Zhao, Qiang

    2015-09-01

    We revisit the compositeness theorem proposed by Weinberg in an effective field theory (EFT) and explore criteria which are sensitive to the structure of S-wave threshold states. On a general basis, we show that the wave function renormalization constant Z, which is the probability of finding an elementary component in the wave function of a threshold state, can be explicitly introduced in the description of the threshold state. As an application of this EFT method, we describe the near-threshold line shape of the D*0D̅0 invariant mass spectrum in B→D*0D̅0K and determine a nonvanishing value of Z. It suggests that the X(3872) as a candidate of the D*0D̅0 molecule may still contain a small cc¯ core. This elementary component, on the one hand, explains its production in the B meson decay via a short-distance mechanism, and on the other hand, is correlated with the D*0D̅0 threshold enhancement observed in the D*0D̅0 invariant mass distributions. Meanwhile, we also show that if Z is non-zero, the near-threshold enhancement of the D*0D̅0 mass spectrum in the B decay will be driven by the short-distance production mechanism. Supported by National Natural Science Foundation of China (11147022, 11035006, 11305137), Chinese Academy of Sciences (KJCX2-EW-N01), Ministry of Science and Technology of China (2009CB825200), DFG and NSFC (11261130311) through funds provided to the Sino-German CRC 110 “Symmetries and the Emergence of Structure in QCD”, and Doctor Foundation of Xinjiang University (BS110104)

  18. ROVIBRATIONAL QUENCHING RATE COEFFICIENTS OF HD IN COLLISIONS WITH He

    SciTech Connect

    Nolte, J. L.; Stancil, P. C.; Lee, T.-G.; Balakrishnan, N.; Forrey, R. C. E-mail: stancil@physast.uga.edu E-mail: naduvala@unlv.nevada.edu

    2012-01-01

    Along with H{sub 2}, HD has been found to play an important role in the cooling of the primordial gas for the formation of the first stars and galaxies. It has also been observed in a variety of cool molecular astrophysical environments. The rate of cooling by HD molecules requires knowledge of collisional rate coefficients with the primary impactors, H, He, and H{sub 2}. To improve knowledge of the collisional properties of HD, we present rate coefficients for the He-HD collision system over a range of collision energies from 10{sup -5} to 5 Multiplication-Sign 10{sup 3} cm{sup -1}. Fully quantum mechanical scattering calculations were performed for initial HD rovibrational states of j = 0 and 1 for v = 0-17 which utilized accurate diatom rovibrational wave functions. Rate coefficients of all {Delta}v = 0, -1, and -2 transitions are reported. Significant discrepancies with previous calculations, which adopted a small basis and harmonic HD wave functions for excited vibrational levels, were found for the highest previously considered vibrational state of v = 3. Applications of the He-HD rate coefficients in various astrophysical environments are briefly discussed.

  19. Variability of Rotational Temperatures from Different OH Rovibrational Levels

    NASA Astrophysics Data System (ADS)

    Vimal, D. V.; Slanger, T. G.

    2011-12-01

    TThe Meinel band emission lines from rovibrationally excited OH in its electronic ground state in the nightglow are widely used as a diagnostic tool to investigate key mesospheric variables such as temperature, tides, and gravity waves. The OH rotational temperature has been extensively studied to ascertain both long- and short-term variability in the upper atmosphere. Current controversy in the literature regarding the possible variability of temperatures deduced from different OH rovibrational levels limits our ability to compare data from different sources. Researchers tend to use a monitoring vibrational level for OH Meinel bands that is most convenient for their instrument. Background sky spectra captured by astronomical instruments provide detailed records of optical emissions in the upper atmosphere. For this study we utilized existing sky spectra from the Keck telescopes in Mauna Kea and the Very Large Telescope in Chile for the OH Meinel bands bound by the extremes (υ = 3, 8). We compared these results with the temperatures deduced from the O2 0-1 Atmospheric band at 865 nm. This latter emission, emanating from a long-lived species, should represent the true kinetic temperature at the altitude of emission and therefore puts a cap on how high the temperature difference can be between the nominal OH altitude (87 km) and the 95-km altitude of the O2 emission. We present the results of our analysis and discuss the implications for mesospheric temperature retrievals from OH emissions. This work was supported by NSF grant ATM-0924781 from NSF CEDAR.

  20. Quantum Calculation of Inelastic CO Collisions with H. III. Rate Coefficients for Ro-vibrational Transitions

    NASA Astrophysics Data System (ADS)

    Song, L.; Balakrishnan, N.; Walker, K. M.; Stancil, P. C.; Thi, W. F.; Kamp, I.; van der Avoird, A.; Groenenboom, G. C.

    2015-11-01

    We present calculated rate coefficients for ro-vibrational transitions of CO in collisions with H atoms for a gas temperature range of 10 K ≤ T ≤ 3000 K, based on the recent three-dimensional ab initio H-CO interaction potential of Song et al. Rate coefficients for ro-vibrational v=1,j=0-30\\to v\\prime =0,j\\prime transitions were obtained from scattering cross sections previously computed with the close-coupling (CC) method by Song et al. Combining these with the rate coefficients for vibrational v=1-5\\to v\\prime \\lt v quenching obtained with the infinite-order sudden approximation, we propose a new extrapolation scheme that yields the rate coefficients for ro-vibrational v=2-5,j=0-30\\to v\\prime ,j\\prime de-excitation. Cross sections and rate coefficients for ro-vibrational v=2,j=0-30\\to v\\prime =1,j\\prime transitions calculated with the CC method confirm the effectiveness of this extrapolation scheme. Our calculated and extrapolated rates are very different from those that have been adopted in the modeling of many astrophysical environments. The current work provides the most comprehensive and accurate set of ro-vibrational de-excitation rate coefficients for the astrophysical modeling of the H-CO collision system. The application of the previously available and new data sets in astrophysical slab models shows that the line fluxes typically change by 20%-70% in high temperature environments (800 K) with an H/H2 ratio of 1; larger changes occur for lower temperatures.

  1. Reaction {pi}N {yields} {pi}{pi}N near threshold

    SciTech Connect

    Frlez, E.

    1993-11-01

    The LAMPF E1179 experiment used the {pi}{sup 0} spectrometer and an array of charged particle range counters to detect and record {pi}{sup +}{pi}{sup 0}, {pi}{sup 0}p, and {pi}{sup +}{pi}{sup 0}p coincidences following the reaction {pi}{sup +}p {yields} {pi}{sup 0}{pi}{sup +}p near threshold. The total cross sections for single pion production were measured at the incident pion kinetic energies 190, 200, 220, 240, and 260 MeV. Absolute normalizations were fixed by measuring {pi}{sup +}p elastic scattering at 260 MeV. A detailed analysis of the {pi}{sup 0} detection efficiency was performed using cosmic ray calibrations and pion single charge exchange measurements with a 30 MeV {pi}{sup {minus}} beam. All published data on {pi}N {yields} {pi}{pi}N, including our results, are simultaneously fitted to yield a common chiral symmetry breaking parameter {xi} ={minus}0.25{plus_minus}0.10. The threshold matrix element {vert_bar}{alpha}{sub 0}({pi}{sup 0}{pi}{sup +}p){vert_bar} determined by linear extrapolation yields the value of the s-wave isospin-2 {pi}{pi} scattering length {alpha}{sub 0}{sup 2}({pi}{pi}) = {minus}0.041{plus_minus}0.003 m{sub {pi}}{sup {minus}1}, within the framework of soft-pion theory.

  2. Influence of the Atomic Potential on Near-Threshold RABBITT Measurements

    NASA Astrophysics Data System (ADS)

    Kiesewetter, Dietrich; Schoun, Stephen; Camper, Antoine; Agostini, Pierre; Dimauro, Louis; Jones, Robert

    2015-05-01

    We have used the RABBITT technique [P. M. Paul et al., Science 292, 1689 (2001)] to study IR-induced continuum transitions involving near-threshold, XUV photoelectrons from He, Ne, and Ar atoms. Energy exchange between ionized electrons and intense oscillating fields plays an essential role in many strong field physics phenomena. For large fields and/or electron energies, the parent ion plays a negligible role in the energy transfer process. This fact is exploited by RABBITT and attosecond streaking techniques for characterizing attosecond pulse trains and isolated pulses, respectively. However, for low energy electrons in weak to moderate dressing fields, the atomic potential influences the energy transfer process, modifying the relative phase and amplitude of photoelectron sidebands in a RABBITT measurement (or the final momentum and apparent photoionization delay in a streaking experiment). For the RABBITT experiments, intense 1.3 micron pulses are used to generate the XUV harmonics for photoionization, and provide the phase-locked dressing field. In principle, the energy-dependence of the measured side-band amplitudes and phases might be used to extract information about the atomic binding potential. Supported by the U.S. DOE, Office of Science, BES, Award # DE-FG02-04ER15614 (LFD) and DE-FG02-00ER15053 (RRJ).

  3. Quantitative prediction of perceptual decisions during near-threshold fear detection

    NASA Astrophysics Data System (ADS)

    Pessoa, Luiz; Padmala, Srikanth

    2005-04-01

    A fundamental goal of cognitive neuroscience is to explain how mental decisions originate from basic neural mechanisms. The goal of the present study was to investigate the neural correlates of perceptual decisions in the context of emotional perception. To probe this question, we investigated how fluctuations in functional MRI (fMRI) signals were correlated with behavioral choice during a near-threshold fear detection task. fMRI signals predicted behavioral choice independently of stimulus properties and task accuracy in a network of brain regions linked to emotional processing: posterior cingulate cortex, medial prefrontal cortex, right inferior frontal gyrus, and left insula. We quantified the link between fMRI signals and behavioral choice in a whole-brain analysis by determining choice probabilities by means of signal-detection theory methods. Our results demonstrate that voxel-wise fMRI signals can reliably predict behavioral choice in a quantitative fashion (choice probabilities ranged from 0.63 to 0.78) at levels comparable to neuronal data. We suggest that the conscious decision that a fearful face has been seen is represented across a network of interconnected brain regions that prepare the organism to appropriately handle emotionally challenging stimuli and that regulate the associated emotional response. decision making | emotion | functional MRI

  4. Generating Molecular Rovibrational Coherence by Two-Photon Femtosecond Photoassociation of Thermally Hot Atoms

    SciTech Connect

    Rybak, Leonid; Levin, Liat; Amitay, Zohar; Amaran, Saieswari; Kosloff, Ronnie; Tomza, Michal; Moszynski, Robert; Koch, Christiane P.

    2011-12-30

    The formation of diatomic molecules with rotational and vibrational coherence is demonstrated experimentally in free-to-bound two-photon femtosecond photoassociation of hot atoms. In a thermal gas at a temperature of 1000 K, pairs of magnesium atoms, colliding in their electronic ground state, are excited into coherent superpositions of bound rovibrational levels in an electronically excited state. The rovibrational coherence is probed by a time-delayed third photon, resulting in quantum beats in the UV fluorescence. A comprehensive theoretical model based on ab initio calculations rationalizes the generation of coherence by Franck-Condon filtering of collision energies and partial waves, quantifying it in terms of an increase in quantum purity of the thermal ensemble. Our results open the way to coherent control of a binary reaction.

  5. Precision Measurement of Electroproduction of pi0 near Threshold

    SciTech Connect

    Chirapatpimol, Khem

    2012-05-01

    Electromagnetic production of neutral pions near threshold is the most basic, lowest energy reaction in which a new hadron is created. The electromagnetic interaction is well understood so measurements of this reaction can yield direct insight into the hadronic production mechanism. During the past three decades there have been many developments in both the measurement and theory of threshold pion production, starting with measurements of photo-production at Saclay in 1986 and at Mainz in 1990. These measurements indicated a surprising discrepancy with so-called Low Energy Theorems (LETs) which are based on quite fundamental symmetries and considerations. Chiral Perturbation Theory (ChPT) is an effective field theoretic description of the nuclear force which contains the underlying symmetries of the force but deals with nucleons and pions rather than quarks and gluons. It has the advantage of being applicable at low energies but requires tuning some parameters to experimental data. Once these parameters have been determined ChPT predicts how the reaction should behave as a function of the kinematic variable. When applied to the reaction, p(γ,π0)p, near threshold it explained the discrepancy with the LETs and made predictions for electroproduction, p(e,e'p)π 0. Electroproduction measurements at Mainz in the 1990's showed a clear discrepancy with these predictions of ChPT; with parameters determined from one set of kinematics the data for a second set lay far from the predicted value. However, recently completed measurements at Mainz disagreed with their previous measurements. In the experiment presented here, measurements of neutral pion electroproduction,p(e,e'p)π0, were made in bins of momentum transfer, Q2, between Q2 = 0.05 [GeV/c]2 and Q2 = 0.15 [GeV/c]0 and of center-of-mass energy, W, between 0 ≤ W ≤ 30 MeV (above threshold). The experiment was performed in Hall A

  6. Near-threshold incoherent ϕ photoproduction on the deuteron: Searching for traces of a resonance

    NASA Astrophysics Data System (ADS)

    Kiswandhi, Alvin; Yang, Shin Nan; Dong, Yu Bing

    2016-07-01

    We study the near-threshold incoherent ϕ photoproduction on the deuteron based on a model of γ N →ϕ N , consisting of Pomeron, (π ,η ) exchanges, and a JP=3 /2- resonance, which describes the low-energy γ p →ϕ p LEPS data well, including the peak in the forward differential cross section. The calculation is done up to double rescatterings, with the spin dependence of the elementary γ N →ϕ N amplitude retained throughout the calculation. The Fermi motion and final-state interactions (FSIs) are all properly treated as prescribed by realistic nucleon-nucleon interaction. The couplings of the resonance to γ n and ϕ n channels are estimated with the help of a constituent quark model. The main features of the LEPS and CLAS data are described reasonably well except for some quantitative discrepancies at very low energies and low-momentum-transfer regions. It is found that contributions of Fermi motion, p n FSI, and resonance are all indispensable in bridging the differences between the single-scattering results and the data. The off-shell rescattering is found to be important because it cancels out a large portion of the on-shell contribution. The discrepancies at low-momentum-transfer regions might be related to the binning size of the data. No peak is found to be associated with the weak resonance because it gets smeared out by the Fermi motion and FSI with the deuterium target. The problem at very-low-energy regions hints at the possible contributions from other mechanisms and should be investigated in depth with the use of recent high-statistics γ p →ϕ p data from CLAS.

  7. Rovibrationally Resolved Photodissociation of HeH+

    NASA Astrophysics Data System (ADS)

    Miyake, S.; Gay, C. D.; Stancil, P. C.

    2011-07-01

    Accurate photodissociation cross sections have been obtained for the A1Σ+ <-- X1Σ+ electronic transition of HeH+ using ab initio potential curves and dipole transition moments. Partial cross sections have been evaluated for all rotational transitions from the vibrational levels v'' = 0-11 and over the entire accessible wavelength range λλ100-1129. Assuming a Boltzmann distribution of the rovibrational levels of the X1Σ+ state, photodissociation cross sections are presented for temperatures between 500 and 12,000 K. A similar set of calculations was performed for the pure rovibrational photodissociation in the X1Σ+ electronic ground state, but covering photon wavelengths into the far-infrared. Applications of the cross sections to the destruction of HeH+ in the early universe and in UV-irradiated environments such as primordial halos and protoplanetary disks are briefly discussed.

  8. Interactions between auditory 'what' and 'where' pathways revealed by enhanced near-threshold discrimination of frequency and position.

    PubMed

    Tardif, Eric; Spierer, Lucas; Clarke, Stephanie; Murray, Micah M

    2008-03-01

    Partially segregated neuronal pathways ("what" and "where" pathways, respectively) are thought to mediate sound recognition and localization. Less studied are interactions between these pathways. In two experiments, we investigated whether near-threshold pitch discrimination sensitivity (d') is altered by supra-threshold task-irrelevant position differences and likewise whether near-threshold position discrimination sensitivity is altered by supra-threshold task-irrelevant pitch differences. Each experiment followed a 2 x 2 within-subjects design regarding changes/no change in the task-relevant and task-irrelevant stimulus dimensions. In Experiment 1, subjects discriminated between 750 Hz and 752 Hz pure tones, and d' for this near-threshold pitch change significantly increased by a factor of 1.09 when accompanied by a task-irrelevant position change of 65 micros interaural time difference (ITD). No response bias was induced by the task-irrelevant position change. In Experiment 2, subjects discriminated between 385 micros and 431 micros ITDs, and d' for this near-threshold position change significantly increased by a factor of 0.73 when accompanied by task-irrelevant pitch changes (6 Hz). In contrast to Experiment 1, task-irrelevant pitch changes induced a response criterion bias toward responding that the two stimuli differed. The collective results are indicative of facilitative interactions between "what" and "where" pathways. By demonstrating how these pathways may cooperate under impoverished listening conditions, our results bear implications for possible neuro-rehabilitation strategies. We discuss our results in terms of the dual-pathway model of auditory processing. PMID:18191423

  9. Experimental and Finite Element Modeling of Near-Threshold Fatigue Crack Growth for the K-Decreasing Test Method

    NASA Technical Reports Server (NTRS)

    Smith, Stephen W.; Seshadri, Banavara R.; Newman, John A.

    2015-01-01

    The experimental methods to determine near-threshold fatigue crack growth rate data are prescribed in ASTM standard E647. To produce near-threshold data at a constant stress ratio (R), the applied stress-intensity factor (K) is decreased as the crack grows based on a specified K-gradient. Consequently, as the fatigue crack growth rate threshold is approached and the crack tip opening displacement decreases, remote crack wake contact may occur due to the plastically deformed crack wake surfaces and shield the growing crack tip resulting in a reduced crack tip driving force and non-representative crack growth rate data. If such data are used to life a component, the evaluation could yield highly non-conservative predictions. Although this anomalous behavior has been shown to be affected by K-gradient, starting K level, residual stresses, environmental assisted cracking, specimen geometry, and material type, the specifications within the standard to avoid this effect are limited to a maximum fatigue crack growth rate and a suggestion for the K-gradient value. This paper provides parallel experimental and computational simulations for the K-decreasing method for two materials (an aluminum alloy, AA 2024-T3 and a titanium alloy, Ti 6-2-2-2-2) to aid in establishing clear understanding of appropriate testing requirements. These simulations investigate the effect of K-gradient, the maximum value of stress-intensity factor applied, and material type. A material independent term is developed to guide in the selection of appropriate test conditions for most engineering alloys. With the use of such a term, near-threshold fatigue crack growth rate tests can be performed at accelerated rates, near-threshold data can be acquired in days instead of weeks without having to establish testing criteria through trial and error, and these data can be acquired for most engineering materials, even those that are produced in relatively small product forms.

  10. Effect of oxidation kinetics on the near threshold fatigue crack growth behavior of a nickel base superalloy

    SciTech Connect

    Yuen, J.L.; Roy, P.; Nix, W.D.

    1984-09-01

    The influence of oxidation kinetics on the near threshold fatigue crack growth behavior of a nickel base precipitation hardened superalloy was studied in air from 427 to 649 C. The tests were conducted at 100 Hz and at load ratios of 0.1 and 0.5. The threshold values of the alternating stress intensity factor were found to increase with temperature. This behavior is attributed to oxide deposits that form on the freshly created fracture surfaces which enhance crack closure. As determined from secondary ion mass spectrometry, the oxide thickness was uniform over the crack length and was of the order of the maximum crack tip opening displacement at threshold. Oxidation kinetics were important in thickening the oxide on the fracture surfaces at elevated temperatures, whereas at room temperature, the oxide deposits at near threshold fatigue crack growth rates and at low load ratios were thickened by an oxide fretting mechanism. The effect of fracture surface roughness-induced crack closure on the near threshold fatigue crack growth behavior is also discussed. 27 references.

  11. Effect of oxidation kinetics on the near threshold fatigue crack growth behavior of a nickel base superalloy

    NASA Astrophysics Data System (ADS)

    Yuen, J. L.; Roy, P.; Nix, W. D.

    1984-09-01

    The influence of oxidation kinetics on the near threshold fatigue crack growth behavior of a nickel base precipitation hardened superalloy was studied in air from 427° to 649 °C. The tests were conducted at 100 Hz and at load ratios of 0.1 and 0.5. The threshold ΔK values were found to increase with temperature. This behavior is attributed to oxide deposits that form on the freshly created fracture surfaces which enhance crack closure. As determined from secondary ion mass spectrometry, the oxide thickness was uniform over the crack length and was of the order of the maximum crack tip opening displacement at threshold. Oxidation kinetics were important in thickening the oxide on the fracture surfaces at elevated temperatures, whereas at room temperature, the oxide deposits at near threshold fatigue crack growth rates and at low load ratios were thickened by an oxide fretting mechanism. The effect of fracture surface roughness-induced crack closure on the near threshold fatigue crack growth behavior is also discussed.

  12. Internal energy distribution of the NCO fragment from near-threshold photolysis of isocyanic acid, HNCO

    SciTech Connect

    Brown, S.S.; Berghout, H.L.; Crim, F.F.

    1996-05-09

    We report the first measurement of the vibrational- and rotational-state distributions in the NCO fragment resulting from photolysis of HNCO. Recent studies have drawn conclusions about the photochemistry of HNCO and the vibrational distribution in the NCO fragment from observations of kinetic energy distribution of the H atom produced in this photolysis; however, there has been no direct observation of the NCO fragment itself. We use laser-induced fluorescence to detect the nascent NCO photoproducts and spectral simulations to extract vibrational-state populations. The rotational distributions, where we can measure them, show little excitation, and the vibrational energy preferentially appears in the bending mode. The vibrational-state distribution results directly from the excited-state geometry of the HNCO parent, in which the NCO group is bent. The dissociation proceeds from this bent NCO group to a linear NCO fragment, strongly exciting the bending mode. We find about 65% of the total energy in relative translation of the fragments, while 30% goes into vibration and 5% into rotation of NCO. 49 refs., 7 figs., 2 tabs.

  13. The design of an intense accelerator-based epithermal neutron beam prototype for BNCT using near-threshold reactions

    NASA Astrophysics Data System (ADS)

    Lee, Charles L.

    Near-threshold boron neutron capture therapy (BNCT) uses proton energies only tens of rev above the (pan) reaction threshold in lithium in order to reduce the moderation requirements of the neutron source. The goals of this research were to prove the feasibility of this near-threshold concept for BNCT applications, using both calculation and experiment, and design a compact neutron source prototype from these results. This required a multidisciplinary development of methods for calculation of neutron yields, head phantom dosimetry, and accelerator target heat removal. First, a method was developed to accurately calculate thick target neutron yields for both near-threshold and higher energy proton beams, in lithium metal as well as lithium compounds. After these yields were experimentally verified, they were used as neutron sources for Monte Carlo (MCNP) simulations of neutron and photon transport in head phantoms. The theoretical and experimental determination of heat removal from a target backing with multiple fins, as well as numerical calculations of heat deposition profiles based on proton energy loss in target and backing materials, demonstrated that lithium integrity can be maintained for proton beam currents up to 2.5 mA. The final design uses a proton beam energy of 1.95 MeV and has a centerline epithermal neutron flux of 2.2 × 108 n/cm2- sec/mA, an advantage depth of 5.7 cm, an advantage ratio of 4.3, and an advantage depth dose rate of 6.7 RBE- cGy/min/mA, corresponding to an irradiation time of 38 minutes with a 5 mA beam. Moderator, reflector, and shielding weigh substantially less than other accelerator BNCT designs based on higher proton energies, e.g. 2.5 MeV. The near-threshold concept is useful as a portable neutron source for hospital settings, with applications ranging from glioblastomas to melanomas and synovectomy. (Copies available exclusively from MIT Libraries, Rm. 14- 0551, Cambridge, MA 02139-4307. Ph. 617-253-5668; Fax 617-253-1690.)

  14. Resonances in Near-Threshold Electron Elastic Scattering Cross Sections for Au and Pt: Identification of Electron Affinities.

    NASA Astrophysics Data System (ADS)

    Felfli, Z.; Msezane, A. Z.; Sokolovski, D.

    2008-05-01

    The near-threshold electron attachment in Au and Pt atoms is investigated as Regge resonances using our recent Regge-pole methodology [1] together with a Thomas-Fermi potential which incorporates the crucial core-polarization interaction. The resultant stable negative ion states are found to have the discernable characteristic of very small imaginary parts of the Regge poles, which translates into long-lived resonances. The near-threshold electron elastic total cross sections for both Au and Pt are characterized by multiple resonances from which we extract the electron affinity (EA) values through the scrutiny of the imaginary part of the relevant complex angular momentum. For Au^- and Pt^- the extracted binding energies of 2.262 eV and 2.163 eV, respectively, are in excellent agreement with the most recently measured EA values for Au [2] and Pt [3]. Ramsauer-Townsend minima, shape resonances and the Wigner threshold behavior are identified in both Au^- and Pt^- ions.[1] D. Sokolovski et al, Phys. Rev. A 76, 012705 (2007)[2] H. Hotop and W. C. Lineberger, J. Chem. Ref. Data 14, 731 (1985)[3] R. C. Bilodeau et al, Phys. Rev. A 61, 012505 (1999)

  15. Near-threshold resonances in electron elastic scattering cross sections for Au and Pt atoms: identification of electron affinities

    NASA Astrophysics Data System (ADS)

    Msezane, A. Z.; Felfli, Z.; Sokolovski, D.

    2008-05-01

    The recent Regge-pole methodology has been employed together with a Thomas-Fermi type potential which incorporates the vital core-polarization interaction to investigate the near-threshold electron attachment in Au and Pt as Regge resonances. The resultant stable negative ion states are found to have the discernible characteristic of very small imaginary parts of the Regge poles, which translate into long-lived resonances. The near-threshold electron elastic total cross sections are characterized by multiple resonances from which we extract the electron affinity (EA) values through the scrutiny of the imaginary part of the relevant complex angular momentum. For the Au- and Pt- negative ions the extracted binding energies of 2.262 eV and 2.163 eV, respectively are in excellent agreement with the most recently measured EA values for Au and Pt. Ramsauer-Townsend minima, shape resonances and the Wigner threshold behaviour are identified in both Au- and Pt- ions.

  16. Rovibrationally Inelastic Collisions of Ultracold Lithium Dimer

    NASA Astrophysics Data System (ADS)

    Jasmine, William; Stewart, Brian

    2016-05-01

    We have calculated cross sections for rovibrationally inelastic collisions of Li2 A(1) 1Σu+ colliding with neon and xenon on ab initio potentials. We find that the inelastic cross section can be very large and increasing at low collision velocity. This behavior is very well modeled as a Langevin process. The total inelastic cross section is a sizable fraction of the total capture cross section, typically about a third. For Li2 - Xe, the total inelastic rate constants are several thousand square angstroms, and level-to-level rate constants are several hundred square angstroms at collision speeds below 1000 cm/s, implying that such collisions might be observable in photoassociated lithium dimer.

  17. The influence of s states near threshold on the structure of light nuclei

    NASA Astrophysics Data System (ADS)

    Hoffman, Calem

    2015-10-01

    A recent work identified the role of neutron s states, and their proximity to the neutron separation threshold, on the ordering of the 1s1 / 2 and 0d5 / 2 single-particle levels in light nuclei. A simple Woods-Saxon potential was used to reproduce the systematic data available for these two levels with great success by accounting for the s state binding energy. This talk will explore other noticeable trends in light nuclei involving neutron s states and utilizing simple potential models determine the role binding energy plays. The trends and calculations will aim to provide descriptions of data and predictions of yet to be found two-particle two-hole excited states in N = 8 and 10 nuclei ranging from Z = 4-9, as well as the energies of mirror states in neutron deficient Al and Na isotopes. Results will be compared with state-of-the-art calculations. Possible future measurements capable of probing these predictions will be discussed as well. This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics, under Contract Number DE-AC02-06CH11357.

  18. Perturbative, R-matrix, and MCHF treatments for near-threshold dielectronic recombination of Si-like ions

    NASA Astrophysics Data System (ADS)

    Kaur, Jagjit; Gorczyca, Thomas; Badnell, Nigel

    2016-05-01

    We present results from a variety of dielectronic recombination (DR) calculations for Si-like ions. A perturbative, multi-configurational Breit-Pauli method is used to calculate DR rate coefficients for the entire Si-like isoelectronic sequence. In addition, we have performed R-matrix and multi-configuration Hartree-Fock (MCHF) calculations to investigate the low-lying resonances that dominate the low-energy, near-threshold region in S2+. This work is motivated by the astrophysical importance of DR of Si-like S2+ in determining the sulfur ionization balance in the Orion nebula, a photoionized plasma corresponding to low-energy electrons. The computed DR rate coefficients comprise part of the assembly of the DR data base required in the modeling of dynamic finite density plasmas.

  19. Pulse-delay effects in the angular distribution of near-threshold EUV + IR two-photon ionization of Ne

    NASA Astrophysics Data System (ADS)

    Mondal, S.; Fukuzawa, H.; Motomura, K.; Tachibana, T.; Nagaya, K.; Sakai, T.; Matsunami, K.; Yase, S.; Yao, M.; Wada, S.; Hayashita, H.; Saito, N.; Callegari, C.; Prince, K. C.; Miron, C.; Nagasono, M.; Togashi, T.; Yabashi, M.; Ishikawa, K. L.; Kazansky, A. K.; Kabachnik, N. M.; Ueda, K.

    2014-01-01

    Photoelectron angular distributions (PADs) from two-photon near-threshold ionization of Ne atoms by the combined action of femtosecond pulses from an extreme ultraviolet (EUV) free-electron laser and infrared (IR) laser have been studied experimentally and theoretically. Solutions of the time-dependent Schrödinger equation indicate that the PADs strongly depend on the time delay between EUV and IR pulses. The experimental results obtained for two extreme cases of completely overlapping and nonoverlapping pulses fully confirm the prediction, illustrating that the measurements of the time-delay dependence of the PAD provide a tool for investigating the fundamental problem of the relative importance of the resonant and nonresonant pathways in the two-color two-photon processes.

  20. Analysis of Rovibrational Resonances Observed in the Microwave Spectrum of FCCCN.

    PubMed

    Okabayashi; Tanaka; Tanaka

    1999-05-01

    Microwave spectrum of fluorocyanoacetylene (FCCCN) produced by a glow discharge in pentafluorobenzonitrile (C6F5CN) was observed using a source modulation spectrometer with a free-space absorption cell. Rotational transitions in the range from J = 9-8 to 53-52 were observed for the vibrationally excited states of nu4 (C&sbond;C stretch), nu5 (CCN bend), nu6 (FCC bend), nu7 (CCC bend), and their associated overtone and combination states up to about 1000 cm-1. Most of the vibrational states above 500 cm-1 are perturbed by rovibrational resonances. The effective vibration-rotation constant of the nu4 state has a negative value (-0.4 MHz), although a vibration-rotation constant generally has a positive value in the excited state of the stretching vibrational mode in a linear molecule. This anomalous behavior is interpreted as due to the rovibrational resonances between the nu4 and several nearby states. By the simultaneous analysis of the states concerned, the unperturbed vibrational energy and rotational constant of the nu4 state are obtained to be 686.50(76) cm-1 and 2068.2387(21) MHz, respectively, where the uncertainties correspond to one standard deviation. Copyright 1999 Academic Press. PMID:10191150

  1. Rovibrational CO analysis in PDR models

    NASA Astrophysics Data System (ADS)

    Stancil, Phillip C.; Cumbee, Renata; Zhang, Ziwei; Walker, Kyle M.; Yang, Benhui; Ferland, Gary J.

    2016-01-01

    CO is one of the most important molecules in the interstellar medium and in photodissociation regions (PDRs). Most of the extragalactic non-stellar IR to submm CO emission originates in PDRs. (Hollenbach & Tielens 1999). Pure rotational CO lines have been previously used in PDR models to provide density, temperature, and other diagnostics. However, for environments exposed to intense UV radiation, CO vibrational levels become significantly populated. Given new calculations of rovibrational collisional rate coefficients for CO-H (Walker et al. 2015, Song et al. 2015) and CO-H2 (Yang et al. 2015), we explore their effects in standard Cloudy PDR (Ferland et al. 2013) and Radex (van der Tak et al. 2007) models. In particular, CO vibrational transitions due to H2 collisions are studied for the first time using reliable full-dimensional CO-H2 collisional data.Ferland, G. J., et al. 2013, Rev. Mex. Astron. y Astrof., 49, 137Hollenbach, D. J. & Tielens, A. G. G. M. 1999, RMP, 71, 173Song, L., et al. 2015, ApJ, in pressvan der Tak, F. F. S, et al. 2007, A&A, 468, 627Walker, K. M., et al. 2015, ApJ, 811, 27Yang, B., et al. 2015, Nature Comm., 6, 6629This work was supported in part by NASA grants NNX12AF42G and NNX15AI61G.

  2. Unstable particles near threshold

    NASA Astrophysics Data System (ADS)

    Chway, Dongjin; Jung, Tae Hyun; Kim, Hyung Do

    2016-07-01

    We explore the physics of unstable particles when the mother particle's mass is approximately the sum of the masses of its daughter particles. In this case, the conventional wave function renormalization factor used for the narrow width approximation is ill-defined. We propose a simple resolution of the problem that allows the use of the narrow width approximation by defining the wave function renormalization factor and the branching ratio in terms of the spectral density. We test new definitions by calculating the cross section in the Higgs portal model and a significant improvement is obtained. Meanwhile, no single decay width can be assigned to the unstable particles and non-exponential decay occurs at all time scales.

  3. Computational study of the rovibrational spectrum of CO₂-CS₂.

    PubMed

    Brown, James; Wang, Xiao-Gang; Carrington, Tucker; Grubbs, G S; Dawes, Richard

    2014-03-21

    A new intermolecular potential energy surface, rovibrational transition frequencies, and line strengths are computed for CO2-CS2. The potential is made by fitting energies obtained from explicitly correlated coupled-cluster calculations using an interpolating moving least squares method. The rovibrational Schrödinger equation is solved with a symmetry-adapted Lanczos algorithm and an uncoupled product basis set. All four intermolecular coordinates are included in the calculation. In agreement with previous experiments, the global minimum of the potential energy surface (PES) is cross shaped. The PES also has slipped-parallel minima. Rovibrational wavefunctions are localized in the cross minima and the slipped-parallel minima. Vibrational parent analysis was used to assign vibrational labels to rovibrational states. Tunneling occurs between the two cross minima. Because more than one symmetry operation interconverts the two wells, the symmetry (-oo) of the upper component of the tunneling doublet is different from the symmetry (-ee) of the tunneling coordinate. This unusual situation is due to the multidimensional nature of the double well tunneling. For the cross ground vibrational state, calculated rotational constants differ from their experimental counterparts by less than 0.0001 cm(-1). Most rovibrational states were found to be incompatible with the standard effective rotational Hamiltonian often used to fit spectra. This appears to be due to coupling between internal and overall rotation of the dimer. A simple 2D model accounting for internal rotation was used for two cross-shaped fundamentals to obtain good fits. PMID:24655176

  4. On the P-wave contributions to the cross sections of t overlinet and t˜overlinet˜ near threshold

    NASA Astrophysics Data System (ADS)

    Mödritsch, Wolfgang

    1996-02-01

    The approach used for the determination of S-wave amplitudes containing the application of the non-relativistic approximation in the case of P-waves leads to unphysical divergencies. We show how to avoid the latter in calculations of contributions to the cross section near threshold in agreement with field theory. This enables us to give quantitatively reliable predictions for the forward-backward asymmetry and for the axial contribution to the total cross section for the top-antitop system. Also the cross section for the production of stop-antistop near threshold is determined.

  5. Crack initiation and near-threshold surface fatigue crack propagation behavior of the iron-base superalloy A-286

    NASA Astrophysics Data System (ADS)

    Daeubler, M. A.; Thompson, A. W.; Bernstein, I. M.

    1988-02-01

    The fatigue behavior of the iron-base superalloy A-286 was studied at room temperature in air for three aging conditions: underaged, peak aged, and overaged. A fatigue strength at 107 cycles of about 200 MPa, independent of aging condition, was measured for an applied load ratio of R =0.1. Surface crack initiation and propagation were measured using hourglass specimens. Surface cracks were invariably initiated in slip bands orientated between 45 and 55 deg to the load axis, and an average ratio of crack depth to crack length of about 0.45 for these semi-elliptical cracks was measured. These earliest observable short surface cracks grew at an accelerated propagation rate in the near-threshold regime but were retarded in a transition stage, resulting in a minimum in crack growth rate. This behavior was correlated to the interaction of the crack with specific microstructure features. Following this minimum, the crack growth accelerated again with increasing Δ K and appeared to converge with the crack growth behavior expected for long through cracks. The crack propagation rate at fixed Δ K was lowest in underaged, compared to peak aged and overaged microstructures. The minimum and trends in crack growth rate appeared to depend on the development of roughness-induced closure.

  6. In-medium and isospin effects on particle production near threshold energies in heavy-ion collisions

    NASA Astrophysics Data System (ADS)

    Feng, Zhao-Qing; Xie, Wen-Jie; Chen, Peng-Hui; Chen, Jie; Jin, Gen-Ming

    2015-10-01

    Dynamics of pseudoscalar mesons (π ,η ,K , and K ¯) and hyperons (Λ and Σ ) produced in heavy-ion collisions near threshold energies has been investigated within the Lanzhou quantum molecular dynamics transport model. The in-medium modifications on particle production in dense nuclear matter are implemented in the model through corrections on the elementary cross sections and by inclusion of the meson-nucleon (or hyperon-nucleon) potentials, in which the isospin effects are considered. It is found that the transportation of particles are influenced with the in-medium corrections. The total number of pions is reduced with an isospin-, density-, and momentum-dependent pion-nucleon potential. However, the ratios of charged pions is enhanced with inclusion of the potential. The production of eta in the domain of midrapidities and high momenta is sensitive to the η -nucleon potential but weakly depends on symmetry energy. The attractive antikaon-nucleon potential enhances the subthreshold K ¯ production and also influences the structure of phase-space distributions. The dynamics of etas, kaons, antikaons, and hyperons is also influenced by the pion potential because of collisions between pions and nucleons (resonances). The impacts of mean-field potentials on particle dynamics are investigated, such as the phase-space distributions from rapidity and transverse momentum spectra, inclusive invariant spectra, collective flows, etc.

  7. LETTER TO THE EDITOR: Near-threshold behaviour of electron elastic scattering cross sections for Fr: a Regge pole analysis

    NASA Astrophysics Data System (ADS)

    Felfli, Z.; Msezane, A. Z.; Sokolovski, D.

    2006-11-01

    Elastic partial and integral cross sections for e--Fr scattering are investigated at electron energies E's near the threshold to understand the mechanism of electron attachment and predict new manifestations. The calculation uses the Mulholland formula, implemented within the complex angular momentum description of scattering wherein resonances are rigorously defined as singularities of the S-matrix. We benchmark our approach by comparing the calculated results with those from the recent Dirac R-matrix method (Bahrim et al 2001 Phys. Rev. A 63 042710). We find that near threshold there is no Ramsauer-Townsend minimum and that there is a shape resonance at E = 0.034 eV, in agreement with the Bahrim et al results. However, contrary to the Dirac R-matrix data, a new sharp f-resonance appears at E = 0.354 eV and a p-wave Wigner threshold behaviour is identified. Some results for e--Cs are also presented. The general agreement with the Dirac R-matrix results gives credence to our simple and novel approach.

  8. Rovibrational energy transfer and dissociation in O2-O collisions.

    PubMed

    Andrienko, Daniil A; Boyd, Iain D

    2016-03-14

    A set of state-specific transition rates for each rovibrational level is generated for the O2(X(3)Σ(g)(-))-O(3)P system using the quasi-classical trajectory method at temperatures observed in hypersonic flows. A system of master equations describes the relaxation of the rovibrational ensemble to thermal equilibrium under ideal heat bath conditions at a constant translational temperature. Vibrational and rotational relaxation times, obtained from the average internal energies, exhibit a pattern inherent in a chemically reactive collisional pair. An intrinsic feature of the O3 molecular system with a large attractive potential is a weak temperature dependence of the rovibrational transition rates. For this reason, the quasi-steady vibrational and rotational temperatures experience a maximum at increasing translational temperature. The energy rate coefficients, that characterize the average loss of internal energy due to dissociation, quickly diminish at high temperatures, compared to other molecular systems. PMID:26979687

  9. Rovibrational energy transfer and dissociation in O2-O collisions

    NASA Astrophysics Data System (ADS)

    Andrienko, Daniil A.; Boyd, Iain D.

    2016-03-01

    A set of state-specific transition rates for each rovibrational level is generated for the O 2 ( X 3 Σg - ) - O (" separators=" 3 P ) system using the quasi-classical trajectory method at temperatures observed in hypersonic flows. A system of master equations describes the relaxation of the rovibrational ensemble to thermal equilibrium under ideal heat bath conditions at a constant translational temperature. Vibrational and rotational relaxation times, obtained from the average internal energies, exhibit a pattern inherent in a chemically reactive collisional pair. An intrinsic feature of the O3 molecular system with a large attractive potential is a weak temperature dependence of the rovibrational transition rates. For this reason, the quasi-steady vibrational and rotational temperatures experience a maximum at increasing translational temperature. The energy rate coefficients, that characterize the average loss of internal energy due to dissociation, quickly diminish at high temperatures, compared to other molecular systems.

  10. Rovibrational Collisional Rates of SiO due to Molecular Hydrogen

    NASA Astrophysics Data System (ADS)

    Yang, Benhui H.; Stancil, Phillip C.; Wang, Xiaohong; Bowman, J.; Zhang, Peng; Naduvalath, Balakrishnan; Forrey, Robert C.

    2016-06-01

    SiO has been detected in a variety of astronomical sources and is a potential diagnostic of dust formation and destruction in star-forming regions and evolved stars. Its rovibrational level populations are perturbed by collisions with He, H and H2 requiring a non-LTE analysis. However, the necessary collisional rate coefficients, and their temperature dependence, are largely unknown. Scattering calculations are the primary source of such rate coefficients. In this work a full-dimensional (6D) potential energy surface (PES) for the SiO-H2 complex was computed using the high-level CCSD(T)-F12B method and fitted using an invariant polynomial approach in 6D. The first full dimensional quantum close-coupling scattering calculations of SiO in collision with H2 on the 6D PES have been performed for the pure state-to-state rotational excitations from SiO(v=0, j=0-10). For rovibrational transitions, state-to-state and total quenching rate coefficients from several low-lying rotational levels of SiO(v=1) are studied for both para-H2 and ortho-H2 collisions.Work at UGA and Emory are supported by NASA grant No. NNX12AF42G, at UNLV by NSF Grant No. PHY-1505557, and at Penn State by NSF Grant No. PHY-1503615.

  11. Rovibrationally inelastic scattering of CN-H2: Full-dimensional close-coupling study

    NASA Astrophysics Data System (ADS)

    Yang, Benhui; Wang, Xiaohong; Stancil, P.; Bowman, J.; Naduvalath, Balakrishnan; Forrey, Robert C.

    2016-01-01

    Rotational and vibrational rate coefficients of CN in collisions with H2 are essential for modeling CN infrared spectra in interstellar gas. We report here full-dimensional potential energy surface (PES) and rovibrational scattering calculations for the CN-H2 collision system.A full-dimensional (6D) PES was calculated using the high-level ab initio CCSD(T)-F12B method. The invariant polynomial method was applied to fit the PES analytically in 6D. Quantum coupled-channel calculations of rotational excitation cross section of CN(j1=4) scattered by para-H2(j2=0, 2) and ortho-H2 (j2=1) were performed for collision energies ranging from 1.0 to 1500 cm-1. State-to-state rate coefficients of CN(j1=4) are computed for H2 rotational states j2=0-2. Comparison of the pure rotational cross sections and rate coefficients were made withprevious available theoretical and experimental results. For the first time we present rovibrational quenching cross sections and rate coefficients of CN in collisions with H2 on the new 6D PES.Work at UGA and Emory are supported by NASA grant NNX12AF42G, at UNLV by NSF Grant PHY-1205838, and at Penn State by NSF Grant PHY-1203228.

  12. State-selective photodissociation dynamics of formaldehyde: Near threshold studies of the H+HCO product channel

    SciTech Connect

    Scott Hopkins, W.; Loock, Hans-Peter; Cronin, Brid; Nix, Michael G. D.; Devine, Adam L.; Dixon, Richard N.; Ashfold, Michael N. R.

    2007-08-14

    The laser-induced photodissociation of formaldehyde in the wavelength range 309<{lambda}<330 nm has been investigated using H (Rydberg) atom photofragment translational spectroscopy. Photolysis wavelengths corresponding to specific rovibronic transitions in the A(tilde sign) {sup 1}A{sub 2}(leftarrow)X(tilde sign) {sup 1}A{sub 1} 2{sub 0}{sup 1}4{sub 0}{sup 3}, 2{sub 0}{sup 2}4{sub 0}{sup 1}, 2{sub 0}{sup 2}4{sub 0}{sup 3}, 2{sub 0}{sup 3}4{sub 0}{sup 1}, and 2{sub 0}{sup 1}5{sub 0}{sup 1} bands of H{sub 2}CO were studied. The total kinetic energy release spectra so derived can be used to determine partial rotational state population distributions of the HCO cofragment. HCO product state distributions have been derived following the population of various different N{sub K{sub a}} levels in the A(tilde sign) {sup 1}A{sub 2} 2{sup 2}4{sup 3} and 2{sup 3}4{sup 1} states. Two distinct spectral signatures are identified, suggesting competition between dissociation pathways involving the X(tilde sign) {sup 1}A{sub 1} and the a(tilde sign) {sup 3}A{sub 2} potential energy surfaces. Most rovibrational states of H{sub 2}CO(A(tilde sign) {sup 1}A{sub 2}) investigated in this work produceH+HCO(X(tilde sign) {sup 2}A{sup '}) photofragments with a broad kinetic energy distribution and significant population in high energy rotational states of HCO. Photodissociation via the A(tilde sign) {sup 1}A{sub 2} 2{sup 2}4{sup 3} 1{sub 1,1} (and 1{sub 1,0}) rovibronic states yields predominantly HCO fragments with low internal energy, a signature that these rovibronic levels are perturbed by the a(tilde sign) {sup 3}A{sub 2} state. The results also suggest the need for further careful measurements of the H+HCO quantum yield from H{sub 2}CO photolysis at energies approaching, and above, the barrier to C-H bond fission on the a(tilde sign) {sup 3}A{sub 2} potential energy surface.

  13. An Empirical Sequence of Disk Gap Opening Revealed by Rovibrational CO

    NASA Astrophysics Data System (ADS)

    Banzatti, A.; Pontoppidan, K. M.

    2015-08-01

    The fundamental rovibrational band of CO near 4.7 μm is a sensitive tracer of the presence and location of molecular gas in the planet-forming region of protoplanetary disks at 0.01-10 AU. We present a new analysis of a high-resolution spectral survey (R ˜ 96,000, or ˜ 3.2 km s-1) of CO rovibrational lines from protoplanetary disks spanning a wide range of stellar masses and of evolutionary properties. We find that the CO emission originates in two distinct velocity components. Line widths of both components correlate strongly with disk inclination, as expected for gas in Keplerian rotation. By measuring the line flux ratios between vibrational transitions Fv=2-1/Fv=1-0, we find that the two velocity components are clearly distinct in excitation. The broad component (FWHM=50-200 km s-1) probes the disk region near the magnetospheric accretion radius at ≈ 0.05 AU, where the gas is hot (800-1500 K). The narrow component (FWHM=10-50 km s-1) probes the disk at larger radii of 0.1-10 AU, where the gas is typically colder (200-700 K). CO excitation temperatures and orbital radii define an empirical temperature-radius relation as a power law with index -0.3 ± 0.1 between 0.05 and 3 AU. The broad CO component, co-spatial with the observed orbital distribution of hot Jupiters, is rarely detected in transitional and Herbig Ae disks, providing evidence for an early dissipation of the innermost disk. An inversion in the temperature profile beyond 3 AU is interpreted as a tracer of a regime dominated by UV pumping in largely devoid inner disks, and may be a signature of the last stage before the disk enters the gas-poor debris phase.

  14. An Empirical Sequence of Disk Gap Opening Revealed by Rovibrational CO

    NASA Astrophysics Data System (ADS)

    Banzatti, A.; Pontoppidan, K. M.

    2015-08-01

    The fundamental rovibrational band of CO near 4.7 μm is a sensitive tracer of the presence and location of molecular gas in the planet-forming region of protoplanetary disks at 0.01–10 AU. We present a new analysis of a high-resolution spectral survey (R ∼ 96,000, or ∼ 3.2 {km} {{{s}}}-1) of CO rovibrational lines from protoplanetary disks spanning a wide range of stellar masses and of evolutionary properties. We find that the CO emission originates in two distinct velocity components. Line widths of both components correlate strongly with disk inclination, as expected for gas in Keplerian rotation. By measuring the line flux ratios between vibrational transitions {F}v=2-1/{F}v=1-0, we find that the two velocity components are clearly distinct in excitation. The broad component ({FWHM}=50-200 {km} {{{s}}}-1) probes the disk region near the magnetospheric accretion radius at ≈ 0.05 AU, where the gas is hot (800-1500 K). The narrow component ({FWHM}=10-50 {km} {{{s}}}-1) probes the disk at larger radii of 0.1–10 AU, where the gas is typically colder (200–700 K). CO excitation temperatures and orbital radii define an empirical temperature–radius relation as a power law with index ‑0.3 ± 0.1 between 0.05 and 3 AU. The broad CO component, co-spatial with the observed orbital distribution of hot Jupiters, is rarely detected in transitional and Herbig Ae disks, providing evidence for an early dissipation of the innermost disk. An inversion in the temperature profile beyond 3 AU is interpreted as a tracer of a regime dominated by UV pumping in largely devoid inner disks, and may be a signature of the last stage before the disk enters the gas-poor debris phase.

  15. Full-dimensional close-coupling study of rovibrationally inelastic scattering of SiO- H2

    NASA Astrophysics Data System (ADS)

    Yang, B.; Wang, X.; Zhang, P.; Stancil, P. C.; Bowman, J. M.; Balakrishnan, N.; Forrey, R. C.

    2016-05-01

    Molecular collisional excitation rate coecients are required to interpret spectra of molecular gas not in local thermodynamic equilibrium. Silicon monoxide (SiO) has been detected in a variety of astronomical sources and is of astrophysical importance. Its rovibrational level populations are perturbed by collisions with He, H and H2. The corresponding collisional rate coefficients and their temperature dependence are largely unknown. Theoretical scattering calculations are the primary source of such rate coefficients. In this work a full-dimensional (6D) potential energy surface (PES) of SiO- H2 was calculated using the high-level CCSD(T)-F12B method and fitted using an invariant polynomial approach in 6D. We performed the first full dimensional quantum close-coupling scattering calculations for SiO in collision with H2 on the 6D PES. Pure state-to-state rotational excitation transitions from SiO(v1 = 0 , j1 = 0-10) are computed. For rovibrational transitions, state-to-state and total quenching cross sections and corresponding rate coefficients from several low-lying rotational levels in the first excited vibrational level of SiO are calculated for both para- H2 and ortho- H2 collisions. Work at UGA and Emory are supported by NASA Grant No. NNX12AF42G, at UNLV by NSF Grant No. PHY-1505557, and at Penn State by NSF Grant No. PHY-1503615.

  16. Characteristics of BDE dependent on 10B concentration for accelerator-based BNCT using near-threshold 7Li(p,n)7Be direct neutrons.

    PubMed

    Tanaka, K; Kobayashi, T; Bengua, G; Nakagawa, Y; Endo, S; Hoshi, M

    2004-11-01

    The characteristics boron-dose enhancer (BDE) was evaluated as to the dependence on the (10)B concentration for BNCT using near-threshold (7)Li(p,n)(7)Be direct neutrons. The treatable protocol depth (TPD) was utilized as an evaluation index. MCNP-4B calculations were performed for near-threshold (7)Li(p,n)(7)Be at a proton energy of 1.900MeV and for a polyethylene BDE. Consequently, the TPD was increased by increasing T/N ratio, i.e., the ratio of the (10)B concentration in the tumor ((10)B(Tumor)) to that in the normal tissue ((10)B(Normal)), and by increasing (10)B(Tumor) and (10)B(Normal) for constant T/N ratio. It has been found that the BDE becomes unnecessary from the viewpoint of increasing the TPD, when (10)B(Tumor) is over a certain level. PMID:15308161

  17. Irradiation characteristics of BNCT using near-threshold 7Li(p, n)7Be direct neutrons: application to intra-operative BNCT for malignant brain tumours.

    PubMed

    Tanaka, Kenichi; Kobayashi, Tooru; Sakurai, Yoshinori; Nakagawa, Yoshinobu; Ishikawa, Masayori; Hoshi, Masaharu

    2002-08-21

    A calculation method for the dosage of neutrons by near-threshold 7Li(p, n)7Be and gamma rays by 7Li(p, p'gamma)7Li was validated through experiments with variable distance between the Li target and the phantom, focusing on large angular dependence. The production of neutrons and gamma rays in the Li target was calculated by Lee's method and their transport in the phantom was calculated using the MCNP-4B code. The dosage in intra-operative boron neutron capture therapy (BNCT) using near-threshold 7Li(p, n)7Be direct neutrons was evaluated using the validated calculation method. The effectiveness of the usage of the direct neutrons was confirmed from the existence of the region satisfying the requirements of the protocol utilized in intra-operative BNCT for brain tumours in Japan. The boron-dose enhancer (BDE) introduced in this paper to increase the contribution of the 10B(n, alpha)7Li dose in the living body was effective. The void utilized to increase the dose in deep regions was also effective with BDE. For the investigation of 1.900 MeV proton beams, for example, it was found that intraoperative BNCT using near-threshold 7Li(p, n)7Be direct neutrons is feasible. PMID:12222863

  18. Ab initio potential energy surface and rovibrational states of HBO

    NASA Astrophysics Data System (ADS)

    Ha, Tae-Kyu; Makarewicz, Jan

    1999-01-01

    The potential energy surface describing the large-amplitude motion of H around the BO core in the HBO molecule has been determined from ab initio calculations. This surface has been sampled by a set of 170 grid points from a two-dimensional space defined by the stretching and the bending coordinates of the H nucleus. At each grid point, the BO bond length has been optimized using the second-order Møller-Plesset perturbation theory with the basis set aug-cc-pVTZ. The surface has a local minimum for the linear as well as the bent configuration of HBO. A low energy barrier to the linear configuration BOH causes a large-amplitude motion and a strong rovibrational interaction in the molecule. Its rovibrational dynamics is different from the dynamics in bent or quasilinear triatomic molecules.

  19. Cold molecules: Formation, ro-vibrational cooling and electronic conversion

    NASA Astrophysics Data System (ADS)

    Horchani, R.

    2016-05-01

    The possibility of controlling all the motion as well as the internal quantum state of a sample of molecules is a long term goal in the cold molecules field. Although many different techniques have been used to produce ultra-cold molecules, in this paper, we will concentrate on the optical pumping technique successfully used to achieve rotational and vibrational cooling of Cs2 molecules. We will review the different photo-association schemes for molecule formation, the detection schemes through photoionization, the ro-vibrational cooling into a single level and finally the electronic conversion. In addition, we will present a theoretical model for both ro-vibrational cooling and electronic conversion that can be used for the preparation of different experiments.

  20. Theoretical studies of electronically excited states

    SciTech Connect

    Besley, Nicholas A.

    2014-10-06

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

  1. Rovibrational analysis of the water bending vibration in the mid-infrared spectrum of atmospherically significant N2-H2O complex

    NASA Astrophysics Data System (ADS)

    Springer, S. D.; McElmurry, B. A.; Wang, Z.; Leonov, I. I.; Lucchese, R. R.; Bevan, J. W.; Coudert, L. H.

    2015-07-01

    Rovibrational transitions associated with tunneling states in the water bending vibration of the atmospherically significant N2-H2O complex have been recorded using a cw supersonic jet quantum cascade laser spectrometer at 6.2 μm. Analysis of the observed spectra is facilitated by incorporating fits of previously recorded microwave and submillimeter data. This accounts for Coriolis coupling to obtain the levels of the ground vibrational state and confirmation of assignment of the excited water bending vibration. The results are used to explore the nature of the associated water bending vibrationally excited states of the complex compared to those in other corresponding water complexes.

  2. Photo- and electroproduction of K{sup 0{Lambda}} near threshold and effects of the K{sup 0} electromagnetic form factor

    SciTech Connect

    Mart, T.

    2011-04-15

    By extending our previous isobar model to the K{sup 0{Lambda}} isospin channel, we investigate the properties of the K{sup 0{Lambda}} photo- and electroproduction at energies near threshold. It is found that the pseudovector coupling yields significantly larger cross sections. Variation of the K{sub 1} coupling constants has significant effect only on the pseudovector model. The electromagnetic form factor of the neutral kaon K{sup 0} is found to have a sizable effect on the longitudinal cross section of the K{sup 0{Lambda}} electroproduction near the threshold.

  3. Destabilizing Effect of Dynamical Friction on Fast-Particle-Driven Waves in a Near-Threshold Nonlinear Regime

    NASA Astrophysics Data System (ADS)

    Lilley, M. K.; Breizman, B. N.; Sharapov, S. E.

    2009-05-01

    The nonlinear evolution of waves excited by the resonant interaction with energetic particles, just above the instability threshold, is shown to depend on the type of relaxation process that restores the unstable distribution function. When dynamical friction dominates over diffusion in the phase space region surrounding the wave-particle resonance, an explosive evolution of the wave is found to be the only solution. This is in contrast with the case of dominant diffusion when the wave may exhibit steady-state, amplitude modulation, chaotic and explosive regimes near marginal stability. The experimentally observed differences between Alfvénic instabilities driven by neutral beam injection and those driven by ion-cyclotron resonance heating are interpreted.

  4. Rovibrational energy transfer in the He-C3 collision: potential energy surface and bound states.

    PubMed

    Denis-Alpizar, Otoniel; Stoecklin, Thierry; Halvick, Philippe

    2014-02-28

    We present a four-dimensional potential energy surface (PES) for the collision of C3 with He. Ab initio calculations were carried out at the coupled-cluster level with single and double excitations and a perturbative treatment of triple excitations, using a quadruple-zeta basis set and mid-bond functions. The global minimum of the potential energy is found to be -26.9 cm(-1) and corresponds to an almost T-shaped structure of the van der Waals complex along with a slightly bent configuration of C3. This PES is used to determine the rovibrational energy levels of the He-C3 complex using the rigid monomer approximation (RMA) and the recently developed atom-rigid bender approach at the Close Coupling level (RB-CC). The calculated dissociation energies are -9.56 cm(-1) and -9.73 cm(-1), respectively at the RMA and RB-CC levels. This is the first theoretical prediction of the bound levels of the He-C3 complex with the bending motion. PMID:24588178

  5. Rovibrationally Inelastic Atom-Molecule Collision Cross Sections from a Hard Sphere Model

    NASA Astrophysics Data System (ADS)

    Lashner, Jacob; Stewart, Brian

    2016-05-01

    Hard-shell models have long been used to elucidate the principal features of molecular energy transfer and exchange reaction in the A + BC system. Nevertheless, no three-dimensional hard-shell calculation of inelastic collision cross sections has been reported. This work aims to fill that void. A particular motivation comes from our experimental results, which show the importance of equatorial impacts in the vibrational excitation process. Working with the simple hard-sphere model, we incorporated secondary impacts, defined as those in which A strikes C after striking B. Such collisions are important in systems such as Li2 - X, in which vibrational energy transfer occurs principally through side impacts. We discuss the complexity this adds to the model and present fully three-dimensional cross sections for rovibrational excitation of an initially stationary molecule in the homonuclear A + B2 system, examining the cross section as a function of the masses and radii of the atoms. We show how the features in the cross section evolve as these parameters are varied and calculate the contribution of secondary (near-equatorial) impacts to the dynamics. We compare with recent measurements in our laboratory and with the results of quasiclassical trajectories.

  6. The ro-vibrational `conveyor belt' for all-optical lasing during laser filamentation in Nitrogen

    NASA Astrophysics Data System (ADS)

    Ivanov, Misha; Richter, Maria; Morales, Felipe; Smirnova, Olga

    2016-05-01

    Inducing and controlling lasing in the open air is an intriguing challenge. Recent experiments on laser filamentation in the air have demonstrated generation of population inversion and lasing on the 391 nm line in the nitrogen ion, which corresponds to the transition between its second excited B2Σu+ and the ground X2Σg+ electronic states. Importantly, lasing at this transition appears to be a very general effect, arising during filamentation of virtually any incident radiation, from visible to mid-infrared. We analyze the possible mechanisms that can be responsible for the generation of the population inversion between the B2Σu+ and X2Σg+ states of N2+,focusing on the interplay between tunnel ionization of neutral nitrogen to different electronic states, ultrafast laser driven electronic excitations in the ion, molecular vibrations, laser induced alignment and rotations. We show how the strong laser field creates a ro-vibrational `conveyor belt' carrying the population away from the ground electronic state X2Σg+ and enabling population inversion in B2Σu+ . We show that this mechanism is robust with respect to the incident laser wavelength, and analyze its optimization with respect to the fundamental wavelength and pulse duration.

  7. Rovibrational states of interstitial H2 in Si

    NASA Astrophysics Data System (ADS)

    Koch, S.; Lavrov, E. V.; Weber, J.

    2011-06-01

    Rovibrational Q(J) transitions of the interstitial H2 molecule in Si have been investigated by Raman scattering in the temperature range 90-388 K. In accordance with an earlier suggestion [M. Hiller, E. V. Lavrov, and J. Weber, Phys. Rev. BPRBMDO1098-012110.1103/PhysRevB.74.235214 74, 235214 (2006)], it is shown that the Q(2) transition of para hydrogen couples to the TAX phonon of Si and appears in the Raman spectra at temperatures above 200 K. The results presented also indicate that the rotational J=3 state of ortho hydrogen is resonantly coupled to the OΓ phonon.

  8. Spectroscopically Accurate Calculations of the Rovibrational Energies of Diatomic Hydrogen

    NASA Astrophysics Data System (ADS)

    Perry, Jason

    2005-05-01

    The Born-Oppenheimer approximation has been used to calculate the rotational and vibrational states of diatomic hydrogen. Because it is an approximation, our group now wants to use a Born-Oppenheimer potential to calculate the electronic energy that has been corrected to match closely with spectroscopic results. We are using a code that has corrections for adiabatic, relativistic, radiative, and non-adiabatic effects. The rovibrational energies have now been calculated for both bound and quasi-bound states. We also want to compute quadrupole transition probabilities for diatomic hydrogen. These calculations aspire to investigate diatomic hydrogen in astrophysical environments.

  9. Mechanistic dissimilarities between environmentally-influenced fatigue-crack propagation at near-threshold and higher growth rates in lower-strength steels

    SciTech Connect

    Suresh, S.; Ritchie, R. O.

    1981-11-01

    The role of hydrogen gas in influencing fatigue crack propagation is examined for several classes of lower strength pressure vessel and piping steels. Based on measurements over a wide range of growth rates from 10/sup -8/ to 10/sup -2/ mm/cycle, crack propagation rates are found to be significantly higher in dehumidified gaseous hydrogen compared to moist air in two distinct regimes of crack growth, namely (i) at the intermediate range of growth typically above approx. 10/sup -5/ mm/cycle, and (ii) at the near-threshold region below approx. 10/sup -6/ mm/cycle approaching lattice dimensions per cycle. Both effects are seen at maximum stress intensities (K/sub max/) far below the sustained-load threshold stress intensity for hydrogen-assisted cracking (K/sub Iscc/). Characteristics of environmentally influenced fatigue crack growth in each regime are shown to be markedly different with regard to fractography and the effect of such variables as load ratio and frequency. It is concluded that the primary mechanisms responsible for the influence of the environment in each regime are distinctly different. Whereas corrosion fatigue behavior at intermediate growth rates can be attributed to hydrogen embrittlement processes, the primary role of moist environments at near-threshold levels is shown to involve a contribution from enhanced crack closure due to the formation of crack surface corrosion deposits at low load ratios.

  10. Quantum dynamics of rovibrational transitions in H2-H2 collisions: internal energy and rotational angular momentum conservation effects.

    PubMed

    Fonseca dos Santos, S; Balakrishnan, N; Lepp, S; Quéméner, G; Forrey, R C; Hinde, R J; Stancil, P C

    2011-06-01

    We present a full dimensional quantum mechanical treatment of collisions between two H(2) molecules over a wide range of energies. Elastic and state-to-state inelastic cross sections for ortho-H(2) + para-H(2) and ortho-H(2) + ortho-H(2) collisions have been computed for different initial rovibrational levels of the molecules. For rovibrationally excited molecules, it has been found that state-to-state transitions are highly specific. Inelastic collisions that conserve the total rotational angular momentum of the diatoms and that involve small changes in the internal energy are found to be highly efficient. The effectiveness of these quasiresonant processes increases with decreasing collision energy and they become highly state-selective at ultracold temperatures. They are found to be more dominant for rotational energy exchange than for vibrational transitions. For non-reactive collisions between ortho- and para-H(2) molecules for which rotational energy exchange is forbidden, the quasiresonant mechanism involves a purely vibrational energy transfer albeit with less efficiency. When inelastic collisions are dominated by a quasiresonant transition calculations using a reduced basis set involving only the quasiresonant channels yield nearly identical results as the full basis set calculation leading to dramatic savings in computational cost. PMID:21663358

  11. ROVIBRATIONALLY RESOLVED PHOTODISSOCIATION OF HeH{sup +}

    SciTech Connect

    Miyake, S.; Gay, C. D.; Stancil, P. C. E-mail: stancil@physast.uga.edu

    2011-07-01

    Accurate photodissociation cross sections have been obtained for the A{sup 1}{Sigma}{sup +} <- X{sup 1}{Sigma}{sup +} electronic transition of HeH{sup +} using ab initio potential curves and dipole transition moments. Partial cross sections have been evaluated for all rotational transitions from the vibrational levels v'' = 0-11 and over the entire accessible wavelength range {lambda}{lambda}100-1129. Assuming a Boltzmann distribution of the rovibrational levels of the X{sup 1}{Sigma}{sup +} state, photodissociation cross sections are presented for temperatures between 500 and 12,000 K. A similar set of calculations was performed for the pure rovibrational photodissociation in the X{sup 1}{Sigma}{sup +} electronic ground state, but covering photon wavelengths into the far-infrared. Applications of the cross sections to the destruction of HeH{sup +} in the early universe and in UV-irradiated environments such as primordial halos and protoplanetary disks are briefly discussed.

  12. Molecular Ro-vibrational Collision Rates for Infrared Modeling of Warm Interstellar Gas from Full-dimensional Quantum Calculations

    NASA Astrophysics Data System (ADS)

    Stancil, Phillip

    We propose to compute accurate collisional excitation rate coefficients for rovibrational transitions of CS, SiO, SO, NO, H_2O, and HCN due to H_2, He, or H impact. This extends our previous grant which focused on 3- and 4-atom systems to 4- and 5-atom collision complexes, with dynamics to be performed on 6-9 dimensional potential energy surfaces (PESs). This work, which uses fully quantum mechanical methods for inelastic scattering and incorporates full-dimensional PESs, pushes beyond the state-of-the-art for such calculations, as recently established by our group for rovibrational transitions in CO-H_2 in 6D. Many of the required PESs will be computed as part of this project using ab initio theory and basis sets of the highest level feasible and particular attention will be given to the long range form of the PESs. The completion of the project will result in 6 new global PESs and state-to-state rate coefficients for a large range of initial rovibrational levels for temperatures between 1 and 3000 K. The chosen collision systems correspond to cases where data are limited or lacking, are important coolants or diagnostics, and result in observable emission features in the infrared (IR). The final project results will be important for the analysis of a variety of interstellar and extragalactic environments in which the local conditions of gas density, radiation field, and/or shocks drive the level populations out of equilibrium. In such cases, collisional excitation data are critical to the accurate prediction and interpretation of observed molecular IR emission lines in protoplanetary disks, star-forming regions, planetary nebulae, embedded protostars, photodissociation regions, etc. The use of the proposed collisional excitation data will lead to deeper examination and understanding of the properties of many astrophysical environments, hence elevating the scientific return from the upcoming JWST, as well as from current (SOFIA, Herschel, HST) and past IR missions

  13. Theoretical ROVibrational Energies (TROVE): A robust numerical approach to the calculation of rovibrational energies for polyatomic molecules

    NASA Astrophysics Data System (ADS)

    Yurchenko, Sergei N.; Thiel, Walter; Jensen, Per

    2007-10-01

    We present a new computational method with associated computer program TROVE (Theoretical ROVibrational Energies) to perform variational calculations of rovibrational energies for general polyatomic molecules of arbitrary structure in isolated electronic states. The (approximate) nuclear kinetic energy operator is represented as an expansion in terms of internal coordinates. The main feature of the computational scheme is a numerical construction of the kinetic energy operator, which is an integral part of the computation process. Thus the scheme is self-contained, i.e., it requires no analytical pre-derivation of the kinetic energy operator. It is also general, since it can be used in connection with any internal coordinates. The method represents an extension of our model for pyramidal XY 3 molecules reported previously [S.N. Yurchenko, M. Carvajal, P. Jensen, H. Lin, J.J. Zheng, W. Thiel, Mol. Phys. 103 (2005) 359]. Non-rigid molecules are treated in the Hougen-Bunker-Johns approach [J.T. Hougen, P.R. Bunker, J.W.C. Johns, J. Mol. Spectrosc. 34 (1970) 136]. In this case, the variational calculations employ a numerical finite basis representation for the large-amplitude motion using basis functions that are generated by Numerov-Cooley integration of the appropriate one-dimensional Schrödinger equation.

  14. Effect of absorbed hydrogen on the microstructure in the vicinity of near-threshold fatigue cracks in low-alloy steel

    SciTech Connect

    Heldt, J.; Kaesche, H.

    1997-12-01

    The influence of a dry hydrogen environment on near-threshold crack growth propagation rates of fatigue cracks in a low-alloy spheroidized steel was investigated. For separation of environmental and mechanically induced effects, fatigue tests in an ultra-high vacuum (UHV) environment were taken as reference. On a macroscopic scale, the authors found a significant acceleration of the propagation rates of cracks exposed to a dry hydrogen atmosphere compared to tests in an inert environment. The electron-microscopic characterization of the microstructure in the vicinity of cracks revealed that the acceleration of fatigue propagation by hydrogen can be rationalized by a hydrogen-involved fatigue damage mechanism. Furthermore, it was concluded that hydrogen enhances the dislocation mobility. This effect aids in the formation of dislocation cellular structure in the cyclic plastic zone. The mode of fracture itself is ductile transgranular and appears to be unchanged by absorption of hydrogen at the crack tip.

  15. Rovibrational bound states of neon trimer: quantum dynamical calculation of all eigenstate energy levels and wavefunctions.

    PubMed

    Yang, Benhui; Chen, Wenwu; Poirier, Bill

    2011-09-01

    Exact quantum dynamics calculations of the eigenstate energy levels and wavefunctions for all bound rovibrational states of the Ne(3) trimer (J = 0-18) have been performed using the ScalIT suite of parallel codes. These codes employ a combination of highly efficient methods, including phase-space optimized discrete variable representation, optimal separable basis, and preconditioned inexact spectral transform methods, together with an effective massive parallelization scheme. The Ne(3) energy levels and wavefunctions were computed using a pair-wise Lennard-Jones potential. Jacobi coordinates were used for the calculations, but to identify just those states belonging to the totally symmetric irreducible representation of the G(12) complete nuclear permutation-inversion group, wavefunctions were plotted in hyperspherical coordinates. "Horseshoe" states were observed above the isomerization barrier, but the horseshoe localization effect is weaker than in Ar(3). The rigid rotor model is found to be applicable for only the ground and first excited vibrational states at low J; fitted rotational constant values are presented. PMID:21913762

  16. Gas Phase Rovibrational Spectroscopy of Dmso, Part II: Towards the Terahertz Observation of 4-FOLD Clusters

    NASA Astrophysics Data System (ADS)

    Cuisset, Arnaud; Martin-Drumel, Marie-Aline; Hindle, Francis; Mouret, Gael; Sadovskii, Dmitrii A.

    2013-06-01

    Benefiting of the exceptional properties of the AILES synchrotron beamline, the gas phase Far-IR spectrum of DMSO has been recorded and resolved. The rovibrational analysis allowed to discover a new rotational behaviour for a polyatomic molecule: the gyroscopic destabilization. In order to explain this phenomenon, we looked for four-fold energy clusters in the high resolution ground state THz spectrum of DMSO recorded with a sub-THz spectrometer based on a frequency multiplication chain. Pure rotational lines in the 5 lowest vibrationnally excited levels have been recorded below 700 GHz. With near 1000 rotational transitions assigned, high quantum numbers have been reached allowing to discover sequence of four-fold clusters in the out of plane bending mode of DMSO and to study the vibrational dependence of an unusual rotational dynamics. J. B. Brubach et al., AIP Conf. Proc., 1214, (81), 2010. A. Cuisset, L. Nanobashvili, I. Smirnova, R. Bocquet, F. Hindle, G. Mouret, O. Pirali, P. Roy, D. Sadovskii,Chem. Phys. Lett., 492,(30),2010 A. Cuisset, O. Pirali, D. Sadovskii,Phys. Rev. Lett., 109,(094101), 2012. G. Mouret, M. Guinet, A. Cuisset, L. Croizet, S. Eliet, R. Bocquet, F. Hindle, IEEE Sensors Journal, 13, 1, 2013.

  17. Near-threshold equal-loudness contours for harbor seals (Phoca vitulina) derived from reaction times during underwater audiometry: a preliminary study.

    PubMed

    Kastelein, Ronald A; Wensveen, Paul J; Terhune, John M; de Jong, Christ A F

    2011-01-01

    Equal-loudness functions describe relationships between the frequencies of sounds and their perceived loudness. This pilot study investigated the possibility of deriving equal-loudness contours based on the assumption that sounds of equal perceived loudness elicit equal reaction times (RTs). During a psychoacoustic underwater hearing study, the responses of two young female harbor seals to tonal signals between 0.125 and 100 kHz were filmed. Frame-by-frame analysis was used to quantify RT (the time between the onset of the sound stimulus and the onset of movement of the seal away from the listening station). Near-threshold equal-latency contours, as surrogates for equal-loudness contours, were estimated from RT-level functions fitted to mean RT data. The closer the received sound pressure level was to the 50% detection hearing threshold, the more slowly the animals reacted to the signal (RT range: 188-982 ms). Equal-latency contours were calculated relative to the RTs shown by each seal at sound levels of 0, 10, and 20 dB above the detection threshold at 1 kHz. Fifty percent detection thresholds are obtained with well-trained subjects actively listening for faint familiar sounds. When calculating audibility ranges of sounds for harbor seals in nature, it may be appropriate to consider levels 20 dB above this threshold. PMID:21303029

  18. Space-time resolved simulation of femtosecond nonlinear light-matter interactions using a holistic quantum atomic model: application to near-threshold harmonics.

    PubMed

    Kolesik, M; Wright, E M; Andreasen, J; Brown, J M; Carlson, D R; Jones, R J

    2012-07-01

    We introduce a new computational approach for femtosecond pulse propagation in the transparency region of gases that permits full resolution in three space dimensions plus time while fully incorporating quantum coherent effects such as high-harmonic generation and strong-field ionization in a holistic fashion. This is achieved by utilizing a one-dimensional model atom with a delta-function potential which allows for a closed-form solution for the nonlinear optical response due to ground-state to continuum transitions. It side-steps evaluation of the wave function, and offers more than one hundred-fold reduction in computation time in comparison to direct solution of the atomic Schrödinger equation. To illustrate the capability of our new computational approach, we apply it to the example of near-threshold harmonic generation in Xenon, and we also present a qualitative comparison between our model and results from an in-house experiment on extreme ultraviolet generation in a femtosecond enhancement cavity. PMID:22772302

  19. Approach to chaos in ultracold atomic and molecular physics: Statistics of near-threshold bound states for Li+CaH and Li+CaF

    NASA Astrophysics Data System (ADS)

    Frye, Matthew D.; Morita, Masato; Vaillant, Christophe L.; Green, Dermot G.; Hutson, Jeremy M.

    2016-05-01

    We calculate near-threshold bound states and Feshbach resonance positions for atom-rigid-rotor models of the highly anisotropic systems Li+CaH and Li+CaF. We perform statistical analysis on the resonance positions to compare with the predictions of random matrix theory. For Li+CaH with total angular momentum J =0 we find fully chaotic behavior in both the nearest-neighbor spacing distribution and the level number variance. However, for J >0 we find different behavior due to the presence of a nearly conserved quantum number. Li+CaF (J =0 ) also shows apparently reduced levels of chaotic behavior despite its stronger effective coupling. This may indicate the development of another good quantum number relating to a bending motion of the complex. However, continuously varying the rotational constant over a wide range shows unexpected structure in the degree of chaotic behavior, including a dramatic reduction around the rotational constant of CaF. This demonstrates the complexity of the relationship between coupling and chaotic behavior.

  20. The structure of disks around Herbig Ae/Be stars as traced by CO ro-vibrational emission

    NASA Astrophysics Data System (ADS)

    van der Plas, G.; van den Ancker, M. E.; Waters, L. B. F. M.; Dominik, C.

    2015-02-01

    Aims: We study the emission and absorption of CO ro-vibrational lines in the spectra of intermediate mass pre-main-sequence stars with the aim to determine both the spatial distribution of the CO gas and its physical properties. We also aim to correlate CO emission properties with disk geometry. Methods: Using high-resolution spectra containing fundamental and first overtone CO ro-vibrational emission, observed with CRIRES on the VLT, we probe the physical properties of the circumstellar gas by studying its kinematics and excitation conditions. Results: We detect and spectrally resolve CO fundamental ro-vibrational emission in 12 of the 13 stars observed, and in two cases in absorption. Conclusions: Keeping in mind that we studied a limited sample, we find that the physical properties and spatial distribution of the CO gas correlate with disk geometry. Flaring disks show highly excited CO fundamental emission up to vu = 5, while self-shadowed disks show CO emission that is not as highly excited. Rotational temperatures range between 250-2000 K. The 13CO rotational temperatures are lower than those of 12CO. The vibrational temperatures in self-shadowed disks are similar to or slightly below the rotational temperatures, suggesting that thermal excitation or IR pumping is important in these lines. In flaring disks the vibrational temperatures reach as high as 6000 K, suggesting fluorescent pumping. Using a simple kinematic model we show that the CO inner radius of the emitting region is ≈10 au for flaring disks and ≤1 au for self-shadowed disks. Comparison with hot dust and other gas tracers shows that CO emission from the disks around Herbig Ae/Be stars, in contrast to T Tauri stars, does not necessarily trace the circumstellar disk up to, or inside the dust sublimation radius, Rsubl. Rather, the onset of the CO emission starts from ≈Rsubl for self-shadowed disks, to tens of Rsubl for flaring disks. It has recently been postulated that group I Herbig stars may

  1. Rovibrational states of Wigner molecules in spherically symmetric confining potentials.

    PubMed

    Cioslowski, Jerzy

    2016-08-01

    The strong-localization limit of three-dimensional Wigner molecules, in which repulsively interacting particles are confined by a weak spherically symmetric potential, is investigated. An explicit prescription for computation of rovibrational wavefunctions and energies that are asymptotically exact at this limit is presented. The prescription is valid for systems with arbitrary angularly-independent interparticle and confining potentials, including those involving Coulombic and screened (i.e., Yukawa/Debye) interactions. The necessary derivations are greatly simplified by explicit constructions of the Eckart frame and the parity-adapted primitive wavefunctions. The performance of the new formalism is illustrated with the three- and four-electron harmonium atoms at their strong-correlation limits. In particular, the involvement of vibrational modes with the E symmetry is readily pinpointed as the origin of the "anomalous" weak-confinement behavior of the (1)S+ state of the four-electron species that is absent in its (1)D+ companion of the strong-confinement regime. PMID:27497548

  2. Experimental rovibrational constants and equilibrium structure of phosphorus trifluoride

    NASA Astrophysics Data System (ADS)

    Najib, Hamid

    2014-11-01

    Thanks to recent high-resolution Fourier transform infrared (FTIR) and pure rotational (RF/CM/MMW) measurements, several experimental values of the rotation-vibration parameters of the oblate molecule PF3 have been extracted, contributing thus to the knowledge of the molecular potential of phosphorus trifluoride. The data used are those of the fundamental, overtone and combination bands studied in the 300-1500 cm-1 range. The new values are in good agreement with ones determined at low resolution, but significantly more accurate. The agreement is excellent with the available values determined by ab initio HF-SCF calculations employing the TZP/TZ2P triple-zeta basis. From the recent experimental rovibrational interaction constants αC and αB, new accurate equilibrium rotational constants Ce and Be have been derived for the symmetric top molecule PF3, which were used to derive the equilibrium geometry of this molecule: re(F-P) = 1.560986 (43) Å; θe(FPF) = 97.566657 (64)°.

  3. Rovibrational states of Wigner molecules in spherically symmetric confining potentials

    NASA Astrophysics Data System (ADS)

    Cioslowski, Jerzy

    2016-08-01

    The strong-localization limit of three-dimensional Wigner molecules, in which repulsively interacting particles are confined by a weak spherically symmetric potential, is investigated. An explicit prescription for computation of rovibrational wavefunctions and energies that are asymptotically exact at this limit is presented. The prescription is valid for systems with arbitrary angularly-independent interparticle and confining potentials, including those involving Coulombic and screened (i.e., Yukawa/Debye) interactions. The necessary derivations are greatly simplified by explicit constructions of the Eckart frame and the parity-adapted primitive wavefunctions. The performance of the new formalism is illustrated with the three- and four-electron harmonium atoms at their strong-correlation limits. In particular, the involvement of vibrational modes with the E symmetry is readily pinpointed as the origin of the "anomalous" weak-confinement behavior of the 1S+ state of the four-electron species that is absent in its 1D+ companion of the strong-confinement regime.

  4. Near-threshold (7)Li(p,n)(7)Be neutrons on the practical conditions using thick Li-target and Gaussian proton energies for BNCT.

    PubMed

    Kobayashi, Tooru; Hayashizaki, Noriyosu; Katabuchi, Tatsuya; Tanaka, Kenichi; Bengua, Gerard; Nakao, Noriaki; Kosako, Kazuaki

    2014-06-01

    The near threshold (7)Li(p,n)(7)Be neutrons generated by incident proton energy having Gaussian distribution with mean energies from 1.85 to 1.95MeV, were studied as a practical neutron source for BNCT wherein an RFQ accelerator and a thick Li-target are used. Gaussian energy distributions with the standard deviation of 0, 10, 20 and 40keV for mean proton energies from 1.85 to 1.95MeV were surveyed in 0.01MeV increments. A thick liquid Li-target whose dimensions were established in our previous experiments (i.e., 1mm-thick with 50mm width and 50mm length) was considered in this study. The suitable incident proton energy and physical dimensions of Pb layer which serves as a gamma absorber and a Polyethylene layer which is used as a BDE were surveyed by means of the concepts of TPD. Dose distribution were calculated by using MCNP5. A proton beam with mean energy of 1.92MeV and a Gaussian energy distribution with a standard deviation of 20keV at a current of 10mA was selected from the viewpoint of irradiation time and practically achievable proton current. The suitable thicknesses of Pb gamma absorber was estimated to be about 3cm. The estimated thickness of the polyethylene BDE was about 24mm for an ideal proton current of 13mA, and was 18mm for a practical proton current of 10mA. PMID:24491682

  5. Conflict Resolution as Near-Threshold Decision-Making: A Spiking Neural Circuit Model with Two-Stage Competition for Antisaccadic Task.

    PubMed

    Lo, Chung-Chuan; Wang, Xiao-Jing

    2016-08-01

    Automatic responses enable us to react quickly and effortlessly, but they often need to be inhibited so that an alternative, voluntary action can take place. To investigate the brain mechanism of controlled behavior, we investigated a biologically-based network model of spiking neurons for inhibitory control. In contrast to a simple race between pro- versus anti-response, our model incorporates a sensorimotor remapping module, and an action-selection module endowed with a "Stop" process through tonic inhibition. Both are under the modulation of rule-dependent control. We tested the model by applying it to the well known antisaccade task in which one must suppress the urge to look toward a visual target that suddenly appears, and shift the gaze diametrically away from the target instead. We found that the two-stage competition is crucial for reproducing the complex behavior and neuronal activity observed in the antisaccade task across multiple brain regions. Notably, our model demonstrates two types of errors: fast and slow. Fast errors result from failing to inhibit the quick automatic responses and therefore exhibit very short response times. Slow errors, in contrast, are due to incorrect decisions in the remapping process and exhibit long response times comparable to those of correct antisaccade responses. The model thus reveals a circuit mechanism for the empirically observed slow errors and broad distributions of erroneous response times in antisaccade. Our work suggests that selecting between competing automatic and voluntary actions in behavioral control can be understood in terms of near-threshold decision-making, sharing a common recurrent (attractor) neural circuit mechanism with discrimination in perception. PMID:27551824

  6. Conflict Resolution as Near-Threshold Decision-Making: A Spiking Neural Circuit Model with Two-Stage Competition for Antisaccadic Task

    PubMed Central

    Wang, Xiao-Jing

    2016-01-01

    Automatic responses enable us to react quickly and effortlessly, but they often need to be inhibited so that an alternative, voluntary action can take place. To investigate the brain mechanism of controlled behavior, we investigated a biologically-based network model of spiking neurons for inhibitory control. In contrast to a simple race between pro- versus anti-response, our model incorporates a sensorimotor remapping module, and an action-selection module endowed with a “Stop” process through tonic inhibition. Both are under the modulation of rule-dependent control. We tested the model by applying it to the well known antisaccade task in which one must suppress the urge to look toward a visual target that suddenly appears, and shift the gaze diametrically away from the target instead. We found that the two-stage competition is crucial for reproducing the complex behavior and neuronal activity observed in the antisaccade task across multiple brain regions. Notably, our model demonstrates two types of errors: fast and slow. Fast errors result from failing to inhibit the quick automatic responses and therefore exhibit very short response times. Slow errors, in contrast, are due to incorrect decisions in the remapping process and exhibit long response times comparable to those of correct antisaccade responses. The model thus reveals a circuit mechanism for the empirically observed slow errors and broad distributions of erroneous response times in antisaccade. Our work suggests that selecting between competing automatic and voluntary actions in behavioral control can be understood in terms of near-threshold decision-making, sharing a common recurrent (attractor) neural circuit mechanism with discrimination in perception. PMID:27551824

  7. Direct Electron Impact Excitation of Rydberg-Valence States of Molecular Nitrogen

    NASA Astrophysics Data System (ADS)

    Malone, C. P.; Johnson, P. V.; Liu, X.; Ajdari, B.; Muleady, S.; Kanik, I.; Khakoo, M. A.

    2012-12-01

    .82eV. This effort is to provide improved cross sections for these RV states, in particular for the b‧ 1Σu+ and c‧4 1Σu+ states, with inclusion of more upper vibrational levels. Future optical emission work should include re-measurements of excitation shape functions of the singlet ungerade states utilizing better spectral resolution than past determinations (e.g., [2,4]) to avoid uncertainties associated with unresolved and/or blended spectral features as well as J-dependent predissociation. Further development of theoretical treatments of N2 excitation is also in need. We will also present analysis of our new low-energy, near-threshold excitation cross sections for the valence states of N2, including a 1Πg (v‧) levels. Acknowledgement: This work was performed at CSUF and JPL, Caltech, under contract with NASA. We gratefully acknowledge financial support through NASA's OPR and PATM programs and NSF-PHY-RUI-0096808 & -0965793 and NSF-AGS-0938223. References: [1] Ajello, J. M., M. H. Stevens, I. Stewart, et al. (2007), GRL, 34, L24204 [2] Ajello, J. M., G. K. James, and B. O. Franklin (1989), PRA, 40, 3524-56 [3] Heays, A. N., B. R. Lewis, S. T. Gibson, et al. (2012), PRA, 85, 012705 [4] James, G. K., J. M. Ajello, B. Franklin, and D. E. Shemansky (1990), JPB, 23, 2055-81 [5] Khakoo, M. A., C. P. Malone, P. V. Johnson, et al. (2008), PRA, 77, 012704 [6] Malone, C. P., P. V. Johnson, X. Liu, et al. (2012), PRA, 85, 062704

  8. Rovibrational energy transfer in the He-C{sub 3} collision: Potential energy surface and bound states

    SciTech Connect

    Denis-Alpizar, Otoniel; Stoecklin, Thierry Halvick, Philippe

    2014-02-28

    We present a four-dimensional potential energy surface (PES) for the collision of C{sub 3} with He. Ab initio calculations were carried out at the coupled-cluster level with single and double excitations and a perturbative treatment of triple excitations, using a quadruple-zeta basis set and mid-bond functions. The global minimum of the potential energy is found to be −26.9 cm{sup −1} and corresponds to an almost T-shaped structure of the van der Waals complex along with a slightly bent configuration of C{sub 3}. This PES is used to determine the rovibrational energy levels of the He-C{sub 3} complex using the rigid monomer approximation (RMA) and the recently developed atom-rigid bender approach at the Close Coupling level (RB-CC). The calculated dissociation energies are −9.56 cm{sup −1} and −9.73 cm{sup −1}, respectively at the RMA and RB-CC levels. This is the first theoretical prediction of the bound levels of the He-C{sub 3} complex with the bending motion.

  9. Evaluation of the characteristics of boron-dose enhancer (BDE) materials for BNCT using near threshold 7Li(p,n)7Be direct neutrons

    NASA Astrophysics Data System (ADS)

    Bengua, Gerard; Kobayashi, Tooru; Tanaka, Kenichi; Nakagawa, Yoshinobu

    2004-03-01

    The characteristics of a number of candidate boron-dose enhancer (BDE) materials for boron neutron capture therapy (BNCT) using near threshold 7Li(p,n)7Be direct neutrons were evaluated based on the treatable protocol depth (TPD), defined in this paper. Simulation calculations were carried out by means of MCNP-4B transport code for candidate BDE materials, namely, (C2H4)n, (C2H3F)n, (C2H2F2)n, (C2HF3)n, (C2D4)n, (C2F4)n, beryllium metal, graphite, D2O and 7LiF. Dose protocols applied were those used for intra-operative BNCT treatment for brain tumour currently used in Japan. The maximum TPD (TPDmax) for each BDE material was found to be between 4 cm and 5 cm in the order of (C2H4)n < (C2H3F)n < (C2H2F2)n < (C2HF3)n < beryllium metal < (C2D4)n < graphite < (C2F4)n < D2O < 7LiF. Based on the small and arbitrary variations in the TPDmax for these materials, an explicit advantage of a candidate BDE material could not be established from the TPDmax alone. The dependence of TPD on BDE thickness was found to be influenced by the type of BDE material. For materials with hydrogen, sharp variations in TPD were observed, while those without hydrogen exhibited more moderate fluctuations in TPD as the BDE thickness was varied. The BDE thickness corresponding to TPDmax (BDE(TPDmax)) was also found to depend on the type of BDE material used. Thicker BDE(TPDmax), obtained mostly for BDE materials without hydrogen, significantly reduced the dose rates within the phantom. The TPDmax, the dependence of TPD on BDE thickness and the BDE (TPDmax) were ascertained as appropriate optimization criteria in choosing suitable BDE materials for BNCT. Among the candidate BDE materials considered in this study, (C2H4)n was judged as the suitable material for near-surface tumours and beryllium metal for deeper tumours based on these optimization criteria and other practical considerations.

  10. Ro-vibrational properties of FeCO in the X ˜ 3Σ- and a ˜ 5Σ- electronic states: A computational molecular spectroscopy study

    NASA Astrophysics Data System (ADS)

    Hirano, Tsuneo; Nagashima, Umpei

    2015-08-01

    The present work complements our previous study of the geometry and electronic structure in the ground and low-lying electronic states of FeCO. Here, we report three-dimensional potential energy surfaces (PESs) for the 3Σ- electronic ground state and its high-spin counterpart, the excited state a ˜ 5Σ-, calculated ab initio at the MR-SDCI+Q_DK3/[5ZP ANO-RCC (Fe, C, O)] level of theory. These PESs are employed in 2nd-order-perturbation-theory and DVR3D calculations of the rotation-vibration energies and ro-vibrationally averaged structures. The equilibrium structures determined from the 3D PESs have re (Fe-C) = 1.7247 Å, re (C-O) = 1.1587 Å, and ∠e (Fe-C-O) = 180° for the X ˜ 3Σ- state, and re (Fe-C) = 1.8429 Å, re (C-O) = 1.1522 Å, and ∠e (Fe-C-O) = 180° for the a ˜ 5Σ- state. The ro-vibrationally averaged structures, determined as expectation values over DVR3D wavefunctions, have < r (Fe-C)>0 = 1.7303 Å, < r (C-O)>0 = 1.1631 Å, and < ∠ (Fe-C-O)>0 = 172.6° for the X ˜ 3Σ- state, and < r (Fe-C)>0 = 1.8471 Å, < r (C-O)>0 = 1.1568 Å, and < ∠ (Fe-C-O)>0 = 171.4° for the a ˜ 5Σ- state. The coordinate-covalent Fe-C bond in the X ˜ 3Σ- state, which elongates significantly as the molecule bends, is shown to exhibit normal large amplitude bending motion with strong coupling (manifested by the large value of the relevant third order force constant) between bending and Fe-C stretching modes. The ionic Fe-C bond in the a ˜ 5Σ- state shows anormal bending behavior due to a severe Fermi resonance which also gives rise to a large coupling between the bending and the Fe-C stretching motions, even though the corresponding third order force constant is small. The Yamada-Winnewisser quasi-linearity parameter γ0 is calculated to be -1.00 and -0.90, values characteristic for a linear molecule, for the X ˜ 3Σ- and a ˜ 5Σ- states, respectively. The ro-vibrationally averaged structures of the X ˜ 3Σ- state are discussed in detail and it is

  11. A theoretical study of the rovibrational levels of the bosonic van der Waals neon trimer.

    PubMed

    Salci, Moses; Levin, Sergey B; Elander, Nils; Yarevsky, Evgeny

    2008-10-01

    The eigenenergies and root mean square radii of the rovibrational levels (J = 0-3) of the weakly bound bosonic van der Waals neon trimer were calculated using a full angular momentum three-dimensional finite element method. The differing results of three previous studies for zero angular momentum are discussed, explained, and compared with the results presented here. PMID:19045087

  12. Rovibrational transitions of the methane-water dimer from intermolecular quantum dynamical computations.

    PubMed

    Sarka, János; Császár, Attila G; Althorpe, Stuart C; Wales, David J; Mátyus, Edit

    2016-08-17

    Rovibrational quantum nuclear motion computations, with J = 0, 1, and 2, are reported for the intermolecular degrees of freedom of the methane-water dimer, where J is the quantum number describing the overall rotation of the complex. The computations provide the first explanation of the far-infrared spectrum of this complex published in J. Chem. Phys., 1994, 100, 863. All experimentally reported rovibrational transitions, up to J = 2, can be assigned to transitions between the theoretically computed levels. The deviation of the experimental and computed rovibrational transitions is 0.5 cm(-1) for the ortho and 2 cm(-1) for the para species with a variance of 0.005 cm(-1). In addition to a lower systematic error, the overall agreement of theory and experiment is also better for the ortho species (involving ortho-H2O). Most importantly, for this species all levels of the 24-fold tunneling splitting manifold corresponding to the zero-point vibration (ZPV) are involved in at least one experimentally reported transition. For the para species there are a few energy levels in the computed ZPV manifold that are not involved in the reported experimental transitions. Furthermore, computed energy levels are identified that correspond to the ZPV tunneling splitting manifold of the secondary minimum structure of the dimer, which presumably appear in rovibrational transitions in the same energy regime as the observed transitions, but have not been experimentally reported. PMID:27390887

  13. Theoretical rovibrational line intensities in the electronic ground state of ozone

    NASA Astrophysics Data System (ADS)

    Diehr, Matthieu; Rosmus, Pavel; Carter, Stuart; Knowles, Peter J.

    2004-01-01

    First-principles calculations of absolute line intensities and rovibrational energies of ozone (16O3) are reported using potential energy and electric dipole moment functions calculated by the internally contracted MRCI approach. The rovibrational energies and eigenfunctions (up to about 8500 cm-1 and J = 64) were obtained variationally with an exact Hamiltonian in internal valence coordinates. More than 4.8 × 106 electric dipole transition matrix elements were calculated for the absolute rovibrational line intensities. They are compared with the values of the HITRAN database. The purely rotational absolute line intensities in the (000) state and the rovibrational intensities for the (001)-(000) band agree to within about 0.3 to 1% for the (010)-(000) band to within about 3 to 4%. Excellent agreement with experiment is also achieved for low-lying overtone and combination bands. Inconsistencies are found for the (100)-(000) band overlapping with the antisymmetric stretching fundamental and also for the (002)-(000) antisymmetric stretching overtone. The generated dipole moment function can be used for predicting the absorption intensities in any of the heavier isotopomers, hot bands or the rates of spontaneous emission.

  14. Rovibrational intensities and electric dipole moment function of the X2 Pi hydroxyl radical

    NASA Technical Reports Server (NTRS)

    Chackerian, C., Jr.; Goorvitch, D.; Benidar, A.; Farrenq, R.; Guelachvili, G.; Martin, P. M.; Abrams, M. C.; Davis, S. P.

    1992-01-01

    Recent work aimed at determining the absolute rovibrational transition intensities for the ground electronic state of the hydroxyl radical is reviewed. Two new sets of Fourier transform emission spectra of OH are described which were recorded at the University of Paris and at the Kitt Peak National Solar Observatory.

  15. Understanding nuclear motions in molecules: Derivation of Eckart frame ro-vibrational Hamiltonian operators via a gateway Hamiltonian operator

    SciTech Connect

    Szalay, Viktor

    2015-05-07

    A new ro-vibrational Hamiltonian operator, named gateway Hamiltonian operator, with exact kinetic energy term, T-hat, is presented. It is in the Eckart frame and it is of the same form as Watson’s normal coordinate Hamiltonian. However, the vibrational coordinates employed are not normal coordinates. The new Hamiltonian is shown to provide easy access to Eckart frame ro-vibrational Hamiltonians with exact T-hat given in terms of any desired set of vibrational coordinates. A general expression of the Eckart frame ro-vibrational Hamiltonian operator is given and some of its properties are discussed.

  16. The Effect of Approximating Some Molecular Integrals in Coupled-Cluster Calculations: Fundamental Frequencies and Rovibrational Spectroscopic Constants of Cyclopropenylidene

    NASA Technical Reports Server (NTRS)

    Lee, Timothy J.; Dateo, Christopher E.

    2005-01-01

    The singles and doubles coupled-cluster method that includes a perturbational estimate of connected triple excitations, denoted CCSD(T), has been used, in conjunction with approximate integral techniques, to compute highly accurate rovibrational spectroscopic constants of cyclopropenylidene, C3H2. The approximate integral technique was proposed in 1994 by Rendell and Lee in order to avoid disk storage and input/output bottlenecks, and today it will also significantly aid in the development of algorithms for distributed memory, massively parallel computer architectures. It is shown in this study that use of approximate integrals does not impact the accuracy of CCSD(T) calculations. In addition, the most accurate spectroscopic data yet for C3H2 is presented based on a CCSD(T)/cc-pVQZ quartic force field that is modified to include the effects of core-valence electron correlation. Cyclopropenylidene is of great astronomical and astrobiological interest because it is the smallest aromatic ringed compound to be positively identified in the interstellar medium, and is thus involved in the prebiotic processing of carbon and hydrogen. The singles and doubles coupled-cluster method that includes a perturbational estimate of

  17. The power of three-dimensional imaging for an unambiguous identification of the ro-vibrational state of H2+,D2+, and HD+

    NASA Astrophysics Data System (ADS)

    Sauza, J. B.; Guillen, C. I.; Duot, A. C.; Andrianarijaona, V. M.

    2015-03-01

    We are presenting a three-dimensional imaging technique that could efficiently measure the ro-vibrational states of small diatomic molecular ions such as H2+in two steps. First, the molecular ion is sent toward a jet of alkali atoms to undergo a resonant dissociative charge exchange. Then, the positions of the fragments and their flight time difference are measured with two position sensitive detectors. From these measurements, we obtained the value of the kinetic energy release, which is directly related to the original vibrational excitation of H2+.This technique scheme was first developed by D. P. de Bruijn and J. Los (Rev. Sci. Intstrum. 53, 1020, 1982). Details and examples will be presented. Authors wish to give special thanks to Pacific Union College Student Senate in Angwin, California, for their financial support.

  18. a Rovibrational Analysis of the Water Bending Vibration in OC-H_2O and a Morphed Potential of the Complex

    NASA Astrophysics Data System (ADS)

    Rivera-Rivera, Luis A.; Springer, Sean D.; McElmurry, Blake A.; Leonov, Igor I.; Lucchese, Robert R.; Bevan, John W.; Coudert, L. H.

    2015-06-01

    Rovibrational transitions associated with tunneling states in the water bending vibration in OC-H_2O complex have been recorded using a supersonic jet quantum cascade laser spectrometer at 6.2 μm. Analysis of the resulting spectra is facilitated by incorporating fits of previously recorded microwave and submillimeter data accounting for Coriolis coupling to obtain the levels of the ground vibrational state. The results were then used to confirm assignment of the vibration and explore the nature of tunneling dynamics in associated vibrationally excited states of the complex. A seven-dimension ab initio interaction potential is constructed for the complex. The available spectroscopic data is used to generated a morphed potential. Previous prediction of the D_0 of the complex will be incorporated in the analysis.

  19. State-selected chemical reaction dynamics at the S matrix level - Final-state specificities of near-threshold processes at low and high energies

    NASA Technical Reports Server (NTRS)

    Chatfield, David C.; Truhlar, Donald G.; Schwenke, David W.

    1992-01-01

    State-to-state reaction probabilities are found to be highly final-state specific at state-selected threshold energies for the reactions O + H2 yield OH + H and H + H2 yield H2 + H. The study includes initial rotational states with quantum numbers 0-15, and the specificity is especially dramatic for the more highly rotationally excited reactants. The analysis is based on accurate quantum mechanical reactive scattering calculations. Final-state specificity is shown in general to increase with the rotational quantum number of the reactant diatom, and the trends are confirmed for both zero and nonzero values of the total angular momentum.

  20. Rovibrational States of ClHCl- Isotopomers: a Joint Theoretical and Spectroscopic Investigation

    NASA Astrophysics Data System (ADS)

    Botschwina, P.; Sebald, P.; Oswald, R.; Kawaguchi, K.

    2012-06-01

    Explicitly correlated coupled cluster theory at the CCSD(T*)-F12b level and two precise spectroscopic constants were used to construct an analytical potential energy function (PEF) for highly anharmonic ClHCl-. From variational calculations with that PEF, a large number of rovibrational energies of different isotopomers were obtained. Theory helped with assignments of lines observed by IR diode laser spectroscopy and enabled to elucidate rather complex and unusual patterns of rovibrational interactions. In addition, transition dipole moments were predicted and analyzed. T. B. Adler, G. Knizia, and H.-J. Werner, J. Chem. Phys. 127, 221106 (2007) G. Knizia, T. B. Adler, and H.-J. Werner, J. Chem. Phys. 130, 054104 (2009). K. Kawaguchi, J. Chem. Phys. 88, 4186 (1988).

  1. Quasiclassical description for rovibrational spectra of tetraatomics: the case of PH 3

    NASA Astrophysics Data System (ADS)

    Kozlovskii, Borislav M.; Petrov, Sergei V.

    2006-12-01

    Some new applications of so-called Rotational Energy Surface (RES) are discussed. As shown before, the method allows to discover some important qualitative features in rovibrational spectra of triatomics - e.g., energy level clustering. While trying to generalize the results, we developed a universal numerical procedure, allowing, particularly, to predict the formation of 6-fold energy clusters in spectra of PH 3 by quasiclassical means.

  2. Raman investigation of ro-vibrational modes of interstitial H2 in Si

    NASA Astrophysics Data System (ADS)

    Koch, S. G.; Lavrov, E. V.; Weber, J.

    2012-08-01

    A Raman scattering study of ro-vibrational transitions Q(J) of the interstitial H2 in Si is presented. It is shown that the Q(2) mode of para hydrogen is coupled to the TAX phonon of Si. The mode appears in the spectra at temperatures above 200 K. The results presented also suggest that the Q(3) transition of ortho hydrogen is resonantly coupled to the OΓ phonon.

  3. Phase Space Distribution Near the Self-Excited Oscillation Threshold

    NASA Astrophysics Data System (ADS)

    Dhayalan, Yuvaraj; Baskin, Ilya; Shlomi, Keren; Buks, Eyal

    2014-05-01

    We study the phase space distribution of an optomechanical cavity near the threshold of self-excited oscillation. A fully on-fiber optomechanical cavity is fabricated by patterning a suspended metallic mirror on the tip of the fiber. Optically induced self-excited oscillation of the suspended mirror is observed above a threshold value of the injected laser power. A theoretical analysis based on the Fokker-Planck equation evaluates the expected phase space distribution near threshold. A tomography technique is employed for extracting phase space distribution from the measured reflected optical power vs time in steady state. Comparison between theory and experimental results allows the extraction of the device parameters.

  4. Measurement of the /sup 12/C(/sup 3/He, /pi//sup +/)/sup 15/N reaction cross section near threshold

    SciTech Connect

    Homolka, J.; Schott, W.; Wagner, W.; Wilhelm, W.; Bent, R.D.; Fatyga, M.; Pollock, R.E.; Saber, M.; Segel, R.E.; Kienle, P.

    1988-12-01

    The pionic fusion reaction /sup 12/C(/sup 3/He,/pi//sup +/)/sup 15/N has been measured at 170.2 and 236.3 MeV bombarding energy using recoil detection. At T/sub <3/He$ = 170.2 MeV the angle-integrated cross section for the population of both the /sup 15/N/sub g.s./ and a broad group of unresolved /sup 15/N excited states between E/sub x/ = 6 and 10 MeV is less than 0.03 nb. At T/sub <3/He$ = 236.3 MeV the total cross section summed over both groups is (0.8 +- 0.2) nb.

  5. An exact variational method to calculate rovibrational spectra of polyatomic molecules with large amplitude motion.

    PubMed

    Yu, Hua-Gen

    2016-08-28

    We report a new full-dimensional variational algorithm to calculate rovibrational spectra of polyatomic molecules using an exact quantum mechanical Hamiltonian. The rovibrational Hamiltonian of system is derived in a set of orthogonal polyspherical coordinates in the body-fixed frame. It is expressed in an explicitly Hermitian form. The Hamiltonian has a universal formulation regardless of the choice of orthogonal polyspherical coordinates and the number of atoms in molecule, which is suitable for developing a general program to study the spectra of many polyatomic systems. An efficient coupled-state approach is also proposed to solve the eigenvalue problem of the Hamiltonian using a multi-layer Lanczos iterative diagonalization approach via a set of direct product basis set in three coordinate groups: radial coordinates, angular variables, and overall rotational angles. A simple set of symmetric top rotational functions is used for the overall rotation whereas a potential-optimized discrete variable representation method is employed in radial coordinates. A set of contracted vibrationally diabatic basis functions is adopted in internal angular variables. Those diabatic functions are first computed using a neural network iterative diagonalization method based on a reduced-dimension Hamiltonian but only once. The final rovibrational energies are computed using a modified Lanczos method for a given total angular momentum J, which is usually fast. Two numerical applications to CH4 and H2CO are given, together with a comparison with previous results. PMID:27586906

  6. Characteristics of boron-dose enhancer dependent on dose protocol and 10B concentration for BNCT using near-threshold 7Li(p,n)7Be direct neutrons

    NASA Astrophysics Data System (ADS)

    Tanaka, Kenichi; Kobayashi, Tooru; Bengua, Gerard; Nakagawa, Yoshinobu; Endo, Satoru; Hoshi, Masaharu

    2005-01-01

    The dependence of boron-dose enhancer (BDE) characteristics on dose protocol and 10B concentration was evaluated for BNCT using near-threshold 7Li(p,n)7Be direct neutrons. The treatable protocol depth (TPD) was utilized as an evaluation index. MCNP calculations were performed for near-threshold 7Li(p,n)7Be at a proton energy of 1.900 MeV and for a polyethylene BDE. The effect of dose protocol on BDE characteristics was reflected in terms of the optimum BDE thickness needed for maximum TPD which was found to be independent of the treatable dose but was observed to vary for different combinations of the tolerance doses for heavy charged particles and gamma rays. For the 10B concentration dependence, the TPD was increased by increasing the T/N ratio, i.e., the ratio of the 10B concentration in the tumour (10BTumour) to that in the normal tissue (10BNormal), and by increasing 10BTumour and 10BNormal at constant T/N ratio. It was found that the use of BDE becomes unnecessary from the viewpoint of increasing the TPD, when 10BTumour is over a certain level which is decided by the conditions of the dose protocol.

  7. Characteristics of boron-dose enhancer dependent on dose protocol and 10B concentration for BNCT using near-threshold 7Li(p,n)7Be direct neutrons.

    PubMed

    Tanaka, Kenichi; Kobayashi, Tooru; Bengua, Gerard; Nakagawa, Yoshinobu; Endo, Satoru; Hoshi, Masaharu

    2005-01-01

    The dependence of boron-dose enhancer (BDE) characteristics on dose protocol and 10B concentration was evaluated for BNCT using near-threshold 7Li(p,n)7Be direct neutrons. The treatable protocol depth (TPD) was utilized as an evaluation index. MCNP calculations were performed for near-threshold 7Li(p,n)7Be at a proton energy of 1.900 MeV and for a polyethylene BDE. The effect of dose protocol on BDE characteristics was reflected in terms of the optimum BDE thickness needed for maximum TPD which was found to be independent of the treatable dose but was observed to vary for different combinations of the tolerance doses for heavy charged particles and gamma rays. For the 10B concentration dependence, the TPD was increased by increasing the T/N ratio, i.e., the ratio of the 10B concentration in the tumour (10B(Tumour)) to that in the normal tissue (10B(Normal)), and by increasing 10B(Tumour) and 10B(Normal) at constant T/N ratio. It was found that the use of BDE becomes unnecessary from the viewpoint of increasing the TPD, when 10B(Tumour) is over a certain level which is decided by the conditions of the dose protocol. PMID:15715430

  8. Vibrationally excited molecular hydrogen near Herschel 36

    SciTech Connect

    Rachford, Brian L.; Snow, Theodore P.; Ross, Teresa L.

    2014-05-10

    We present the first high resolution UV spectra toward Herschel 36, a Trapezium-like system of high-mass stars contained within the Lagoon Nebula (M8, NGC 6523). The spectra reveal extreme rovibrational excitation of molecular hydrogen in material at a single velocity or very small range of velocities, with this component presumably lying near the star system and undergoing fluorescent excitation. The overall H{sub 2} excitation is similar to, but apparently larger than, that seen toward HD 37903 which previously showed the largest vibrationally excited H{sub 2} column densities seen in UV absorption spectra. While the velocities of the highly excited H{sub 2} lines are consistent within each observation, it appears that they underwent a ∼60 km s{sup –1} redshift during the 3.6 yr between observations. In neither case does the velocity of the highly excited material match the velocity of the bulk of the line-of-sight material which appears to mostly be in the foreground of M8. Recent work shows unusually excited CH and CH{sup +} lines and several unusually broad diffuse interstellar bands toward Herschel 36. Along with the H{sub 2} excitation, all of these findings appear to be related to the extreme environment within ∼0.1 pc of the massive young stellar system.

  9. Fourier transform infrared spectra in the regions near 1900 and 700 cm -1 and rovibrational analyses of the {ν 1}/{ν 4} and {ν 2}/{ν 5} fundamentals of unstable H 3SnCl, H 3SnBr, and H 3Snl studied as monoisotopic species

    NASA Astrophysics Data System (ADS)

    Bürger, Hans; Betzel, Martina; Schulz, Petra

    1987-01-01

    The IR fundamentals {ν 1}/{ν 4} near 1900 cm -1 and {ν 2}/{ν 5} near 700 cm -1 of the unstable stannyl halides H 3116Sn 35Cl, H 3116Sn 79Br, and H 3116SnI have been studied as monoisotopic species by FT spectroscopy. With a resolution of ˜0.04 cm -1, rotational J and K structure has been resolved at least in part, and rovibrational analyses have been performed. Typically, 500 data of each {a 1}/{e} band have been fitted with σ = 5 × 10 -3 cm -1. Excited state rovibrational parameters complete to second order have been determined. A HOFF-based harmonic force field has been computed, and ground state parameters and ground state geometries have been deduced by combining all presently available data. A strong Coriolis interaction between ν2 and ν5 is revealed, while the interaction between ν1 and ν4 was found to be weak. Perturbations by multiply excited rovibrational levels are important for ν4 of H 3116Sn 79Br, while all other bands (with the exception of a weak local perturbation of ν5 by 2 ν3 in H 3116Sn 35CL) appeared to be unperturbed.

  10. Multiphoton population transfer between rovibrational states of HF

    NASA Astrophysics Data System (ADS)

    Topcu, Turker; Robicheaux, Francis

    2011-05-01

    Efficient population transfer by adiabatically chirping through a multiphoton resonance in microwave driven and impulsively kicked Rydberg atoms has been reported both experimentally and theoretically. Previous work has demonstrated that the physical mechanism responsible for the transition can be viewed as a classical process in phase space as well as a quantum mechanical resonant transition. Here we report on our classical and quantum mechanical simulations in which we have exploited this mechanism to vibrationally excite an HF molecule up to | ν = 4 , J > from its ground state using an intense IR pulse. We compare one-dimensional quantum and classical models where there are no rotational degrees of freedom. We find that for low laser intensities, the transition is classically forbidden although it occurs quantum mechanically through tunneling. We show that for larger peak intensities, the transfer can be looked upon as a classical transition in phase space, similar to that observed in the atomic case. We extend our simulations to fully three-dimensional quantum calculations and investigate the effect of coupling between different rotational pathways. We briefly discuss the effect of thermal averaging over the final J-states. This work was supported by the Office of Basic Energy Sciences, U.S. Department of Energy.

  11. Rovibrational coupling in molecular nitrogen at high temperature: An atomic-level study

    NASA Astrophysics Data System (ADS)

    Valentini, Paolo; Norman, Paul; Zhang, Chonglin; Schwartzentruber, Thomas E.

    2014-05-01

    This article contains an atomic-level numerical investigation of rovibrational relaxation in molecular nitrogen at high temperature (>4000 K), neglecting dissociation. We conduct our study with the use of pure Molecular Dynamics (MD) and Classical Trajectory Calculations (CTC) Direct Simulation Monte Carlo (DSMC), verified to produce statistically identical results at the conditions of interest here. MD and CTC DSMC solely rely on the specification of a potential energy surface: in this work, the site-site Ling-Rigby potential. Additionally, dissociation is prevented by modeling the N-N bond either as a harmonic or an anharmonic spring. The selected molecular model was shown to (i) recover the shear viscosity (obtained from equilibrium pure MD Green-Kubo calculations) of molecular nitrogen over a wide range of temperatures, up to dissociation; (ii) predict well the near-equilibrium rotational relaxation behavior of N2; (iii) reproduce vibrational relaxation times in excellent accordance with the Millikan-White correlation and previous semi-classical trajectory calculations in the low temperature range, i.e., between 4000 K and 10 000 K. By simulating isothermal relaxations in a periodic box, we found that the traditional two-temperature model assumptions become invalid at high temperatures (>10 000 K), due to a significant coupling between rotational and vibrational modes for bound states. This led us to add a modification to both the Jeans and the Landau-Teller equations to include a coupling term, essentially described by an additional relaxation time for internal energy equilibration. The degree of anharmonicity of the N2 bond determines the strength of the rovibrational coupling. Although neglecting N2 dissociation only provides a partial description of a nitrogen system at very high temperatures, high-energy trends for bound-bound transitions are essential to understand nonequilibrium gas flows, with possible implications on rovibration/chemistry interaction

  12. Variability in the CO ro-vibrational lines from HD163296

    NASA Astrophysics Data System (ADS)

    Hein Bertelsen, Rosina P.; Kamp, I.; van der Plas, G.; van den Ancker, M. E.; Waters, L. B. F. M.; Thi, W.-F.; Woitke, P.

    2016-05-01

    We present for the first time a direct comparison of multi-epoch (2001-2002 and 2012) CO ro-vibrational emission lines from HD 163296. We find that both the line shapes and the FWHM (full width at half-maximum) differ between these two epochs. The FWHM of the median observed line profiles are 10-25 km s-1 larger in the earlier epoch, and confirmed double peaks are only present in high J lines from 2001 to 2002. The line wings of individual transitions are similar in the two epochs making an additional central component in the later epoch a likely explanation for the single peaks and the lower FWHM. Variations in near-infrared brightness have been reported and could be linked to the observed variations. Additionally, we use the thermo-chemical disc code PRODIMO to compare for the first time the line shapes, peak separations, FWHM, and line fluxes, to those observed. The PRODIMO model reproduces the peak separations, and low and mid J line fluxes well. The FWHM however, are overpredicted and high J line fluxes are underpredicted. We propose that a variable non-Keplerian component of the CO ro-vibrational emission, such as a disc wind or an episodic accretion funnel, is causing the difference between the two data sets collected at different epochs, and between model and observations. Additional CO ro-vibrational line detections (with cryogenic high-resolution infrared echelle spectrograph/Very Large Telescope (VLT) or Near InfraRed SPECtrometer/Keck) or [Ne II] line observations with VLT Imager and Spectrometer for mid Infrared/VLT could help to clarify the cause of the variability.

  13. Rovibrational coupling in molecular nitrogen at high temperature: An atomic-level study

    SciTech Connect

    Valentini, Paolo Norman, Paul Zhang, Chonglin Schwartzentruber, Thomas E.

    2014-05-15

    This article contains an atomic-level numerical investigation of rovibrational relaxation in molecular nitrogen at high temperature (>4000 K), neglecting dissociation. We conduct our study with the use of pure Molecular Dynamics (MD) and Classical Trajectory Calculations (CTC) Direct Simulation Monte Carlo (DSMC), verified to produce statistically identical results at the conditions of interest here. MD and CTC DSMC solely rely on the specification of a potential energy surface: in this work, the site-site Ling-Rigby potential. Additionally, dissociation is prevented by modeling the N–N bond either as a harmonic or an anharmonic spring. The selected molecular model was shown to (i) recover the shear viscosity (obtained from equilibrium pure MD Green-Kubo calculations) of molecular nitrogen over a wide range of temperatures, up to dissociation; (ii) predict well the near-equilibrium rotational relaxation behavior of N{sub 2}; (iii) reproduce vibrational relaxation times in excellent accordance with the Millikan-White correlation and previous semi-classical trajectory calculations in the low temperature range, i.e., between 4000 K and 10 000 K. By simulating isothermal relaxations in a periodic box, we found that the traditional two-temperature model assumptions become invalid at high temperatures (>10 000 K), due to a significant coupling between rotational and vibrational modes for bound states. This led us to add a modification to both the Jeans and the Landau-Teller equations to include a coupling term, essentially described by an additional relaxation time for internal energy equilibration. The degree of anharmonicity of the N{sub 2} bond determines the strength of the rovibrational coupling. Although neglecting N{sub 2} dissociation only provides a partial description of a nitrogen system at very high temperatures, high-energy trends for bound-bound transitions are essential to understand nonequilibrium gas flows, with possible implications on rovibration

  14. Rotational spectroscopy of isotopologues of silicon monoxide, SiO, and spectroscopic parameters from a combined fit of rotational and rovibrational data.

    PubMed

    Müller, Holger S P; Spezzano, Silvia; Bizzocchi, Luca; Gottlieb, Carl A; Degli Esposti, Claudio; McCarthy, Michael C

    2013-12-19

    Pure rotational transitions of silicon monoxide, involving the main ((28)Si(16)O) as well as several rare isotopic species, were observed in their ground vibrational states by employing long-path absorption spectroscopy between 86 and 825 GHz (1 ≤ J" ≤ 18). Fourier transform microwave spectroscopy was used to study the J" = 0 transition frequencies in the ground and several vibrationally excited states. The vibrational excitation of the newly studied isotopologues extend to between υ = 9 and 29 for (28)Si(17)O and (30)Si(16)O, respectively. Data were extended for some previously investigated species up to υ = 51 for the main isotopologue. The high spectral resolution allowed us to resolve the hyperfine structure in (28)Si(17)O caused by the nuclear electric quadrupole and magnetic dipole moments of (17)O for the first time, and to resolve the much smaller nuclear spin-rotation splitting for isotopic species containing (29)Si. These data were combined with previous rotational and rovibrational (infrared) data to determine an improved set of spectroscopic parameters of SiO in one global fit which takes the breakdown of the Born-Oppenheimer approximation into account. Highly accurate rotational transition frequencies for this important astronomical molecule can now be predicted well into the terahertz region with this parameter set. In addition, a more complete comparison among physical properties of group 14/16 diatomics is possible. PMID:24070172

  15. Molecular line lists: The ro-vibrational spectra of NaF and KF

    NASA Astrophysics Data System (ADS)

    Frohman, Daniel J.; Bernath, Peter F.; Brooke, James S. A.

    2016-01-01

    Rotation-vibration line lists for 23Na19F, 39K19F, and 41K19F in their ground electronic states are presented. Experimental data previously collected for infrared transitions up to v=8 and v=9 for KF [1] and NaF [2], respectively, and for pure rotational transitions have been used to construct potential energy curves to yield ro-vibrational energy levels. Dipole moment functions were generated from ab initio calculations using the SA-CASSCF and ACPF methods. Full line lists and partition functions are made available as supplementary data.

  16. Rovibrational hybrid fs/ps CARS using a volume Bragg grating for N₂ thermometry.

    PubMed

    Scherman, M; Nafa, M; Schmid, T; Godard, A; Bresson, A; Attal-Tretout, B; Joubert, P

    2016-02-01

    Coherent anti-Stokes Raman scattering (CARS) spectra of N2 in the hybrid femtosecond/picosecond regime have been recorded with 0.7  cm(-1) resolution. The Q-branch rovibrational structure has been resolved, making it suitable for gas-phase simultaneous rotational and vibrational thermometry applications. Resolving this spectral structure requires synchronization of a narrowband picosecond probe pulse with a broadband femtosecond pair of pump and Stokes pulses. It is achieved using a single femtosecond ytterbium-laser source and a volume Bragg grating in a compact experimental arrangement. PMID:26907404

  17. Predicting inelastic rovibrational state distributions from an energy constrained angular momentum mechanism

    NASA Astrophysics Data System (ADS)

    Marsh, R. J.; McCaffery, A. J.

    2001-06-01

    We present a quantitative version of the velocity-angular momentum plots of Besley et al. that we have used extensively to represent the key processes at work in collisional transfer mechanisms. Rotational state distributions are obtained by incorporating probability distributions of the relevant variables, and the Monte Carlo (MC) trajectory technique is used to sample these distributions. The method is illustrated with the case of weakly quasi-resonant vibration rotation transfer in A( 1Σ u+) Li2+ Ne collisions. The results show excellent agreement with published experimental data, indicating the apparent dominance of the factors governing angular momentum (AM) conversion in shaping rovibrational distributions.

  18. Full-Dimensional Potential Energy Surface and Ro-vibrational Levels of Dioxirane.

    PubMed

    Li, Jun; Guo, Hua

    2016-05-19

    A full-dimensional potential energy surface is developed for dioxirane based on a high-fidelity fit of ∼46,000 ab initio points at the CCSD(T)-F12a/AVTZ level. The ro-vibrational levels of dioxirane were computed using the MULTIMODE method on this potential energy surface, and the agreement with the available experimental microwave spectrum is quite satisfactory. In addition, dipole moment surfaces have been constructed from ab initio data, and they allow the prediction of the infrared (IR) spectrum. PMID:26422048

  19. Towards inclusion of excited vibrational states in ultracold molecule-molecule quantum scattering calculations

    NASA Astrophysics Data System (ADS)

    Ticknor, Christopher; Kendrick, Brian

    2016-05-01

    We report progress towards including excited vibrational states in quantum scattering calculations of NaK-NaK at ultracold temperatures. We systematically use all pair potentials to build a complete 4 body potential energy surface. We study this 4-body potential and the asymptotic ro-vibrational 2-body basis. This allows for a more complete interaction as two molecules approach each other. We study where and how vibrationally excited states influence the asymptotic 2-body ro-vibrational scattering potentials. This work is an intermediate step in performing the complete scattering calculations as we develop tools to bring together the long range, ultracold 2-body scattering problem and the short range 4-body quantum chemistry problem.

  20. Jost function description of near threshold resonances

    NASA Astrophysics Data System (ADS)

    Simbotin, I.; Shu, D.; Côté, R.

    2015-05-01

    The low energy behavior of cross sections for any scattering problem can be drastically affected by the presence of a resonance near the threshold. In this work, we show that any such strong dependence on energy can be accounted for in terms of the much simpler behavior of the Jost function. Although this is an old idea, see, and despite its advantages, it has not been employed widely. However, this method provides not only a theoretical tool for scattering problems in general, but also a convenient numerical approach in practice. Partially supported by AFOSR (IS), NSF (DS), and ARO (RC).

  1. Kaon photoproduction and electroproduction near threshold

    SciTech Connect

    Mart, T.

    2011-10-21

    We analyze the electromagnetic production of K{sup +}{Lambda} and K{sup 0}{Lambda} near their production thresholds by using isobar models. In the K{sup +}{Lambda} channel we show that the model can nicely describe the available experimental data. In the K{sup 0}{Lambda} channel we demonstrate that the K{sup 0} charge form factor has sizable effects on the longitudinal cross section. By extending the model up to W = 1730 MeV, we are able to observe the existence of the narrow P{sub 11}(J{sup p} = 1/2{sup +}) resonance in the kaon photoproduction process. It is found that the most convincing mass (width) of this resonance is 1650 MeV(5 MeV).

  2. Near threshold studies of photoelectron satellites

    SciTech Connect

    Heimann, P.A.

    1986-11-01

    Photoelectron spectroscopy and synchrotron radiation have been used to study correlation effects in the rare gases: He, Ne, Ar, Kr, and Xe. Two kinds of time-of-flight electron analyzers were employed to examine photoionization very close to threshold and at higher kinetic energies. Partial cross sections and angular distributions have been measured for a number of photoelectron satellites. The shake-off probability has been determined at some inner-shell resonances. 121 refs., 28 figs., 13 tabs.

  3. Baryonia and near-threshold enhancements

    NASA Astrophysics Data System (ADS)

    Deng, Chengrong; Ping, Jialun; Yang, Youchang; Wang, Fan

    2013-10-01

    The baryon-antibaryon spectrum consisting of u, d, s, c, and b quarks is studied in the color flux-tube model with a multibody confinement interaction. Numerical results indicate that many low-spin (S≤1) baryon-antibaryon states can form compact bound states and are stable against decaying into a baryon and an antibaryon. They can be searched for in e+e- annihilation and charmonium or bottomonium decay if they really exist. Multibody confinement interaction as a binding mechanism plays an important role in the formation of the baryon-antibaryon bound states; chromomagnetic interaction also provides a strong attraction in many low-spin baryon-antibaryon states. The newly reported states, X(1835), X(2370), Y(2175), Y(4360), and Yb(10890), might be interpreted as NN¯, ΔΔ¯, ΛΛ¯, ΛcΛ¯c, and ΛbΛ¯b bound states, respectively.

  4. Reduced dimension rovibrational variational calculations of the S(1) state of C2H2. II. The S(1) rovibrational manifold and the effects of isomerization.

    PubMed

    Changala, P Bryan; Baraban, Joshua H; Stanton, John F; Merer, Anthony J; Field, Robert W

    2014-01-14

    Reduced dimension variational calculations have been performed for the rovibrational level structure of the S1 state of acetylene. The state exhibits an unusually complicated level structure, for various reasons. First, the potential energy surface has two accessible conformers, trans and cis. The cis conformer lies about 2700 cm(-1) above the trans, and the barrier to cis-trans isomerization lies about 5000 cm(-1) above the trans minimum. The trans vibrations ν4 (torsion) and ν6 (asym. bend) interact very strongly by Darling-Dennison and Coriolis resonances, such that their combination levels and overtones form polyads with unexpected structures. Both conformers exhibit very large x36 cross-anharmonicity since the pathway to isomerization is a combination of ν6 and ν3 (sym. bend). Near the isomerization barrier, the vibrational levels show an even-odd K-staggering of their rotational levels as a result of quantum mechanical tunneling through the barrier. The present calculations address all of these complications, and reproduce the observed K-structures of the bending and C-C stretching levels with good qualitative accuracy. It is expected that they will assist with the assignment of the irregular patterns near the isomerization barrier. PMID:24437883

  5. Formation of Alkali Hydrides via Two-photon Excitation

    NASA Astrophysics Data System (ADS)

    Juarros, Elizabeth; Kirby, Kate; Coté, Robin

    2006-05-01

    Alkali hydride molecules are very polar, exhibiting large ground-state dipole moments. Ultracold sources of alkali atoms and hydrogen have been created in the laboratory. We explore theoretically the feasibility of forming such molecules from a mixture of the ultracold atomic gases, employing a two-photon stimulated radiative association process -- Raman excitation. The triplet ground state for lithium hydride is of particular interest since it supports only one bound ro-vibrational level. Using accurate molecular potential energy curves and dipole transition moments, we have calculated the rate coefficients for populating the bound ro-vibrational level of the a^3&+circ; state of LiH via the excited b^3π state. We have found that significant molecule formation rates can be realized with laser intensities and atomic densities that are attainable experimentally. Also, we have calculated the rate coefficients for populating all the vibrational levels of the X^1&+circ; state of LiH via the excited B^1π state. In this case, we have found that significant formation rates into the upper vibrational levels can be realized. We examine the spontaneous emission cascade which takes place from these upper vibrational levels on a timescale of milliseconds, and calculate the resulting rotational populations in v=0. We show that photon emission in the cascade process does not contribute to trap loss.

  6. Cryogenic exciter

    SciTech Connect

    Bray, James William; Garces, Luis Jose

    2012-03-13

    The disclosed technology is a cryogenic static exciter. The cryogenic static exciter is connected to a synchronous electric machine that has a field winding. The synchronous electric machine is cooled via a refrigerator or cryogen like liquid nitrogen. The static exciter is in communication with the field winding and is operating at ambient temperature. The static exciter receives cooling from a refrigerator or cryogen source, which may also service the synchronous machine, to selected areas of the static exciter and the cooling selectively reduces the operating temperature of the selected areas of the static exciter.

  7. Rovibrational spectroscopy using a kinetic energy operator in Eckart frame and the multi-configuration time-dependent Hartree (MCTDH) approach

    SciTech Connect

    Sadri, Keyvan Meyer, Hans-Dieter; Lauvergnat, David; Gatti, Fabien

    2014-09-21

    For computational rovibrational spectroscopy the choice of the frame is critical for an approximate separation of overall rotation from internal motions. To minimize the coupling between internal coordinates and rotation, Eckart proposed a condition [“Some studies concerning rotating axes and polyatomic molecules,” Phys. Rev. 47, 552–558 (1935)] and a frame that fulfills this condition is hence called an Eckart frame. A method is developed to introduce in a systematic way the Eckart frame for the expression of the kinetic energy operator (KEO) in the polyspherical approach. The computed energy levels of a water molecule are compared with those obtained using a KEO in the standard definition of the Body-fixed frame of the polyspherical approach. The KEO in the Eckart frame leads to a faster convergence especially for large J states and vibrationally excited states. To provide an example with more degrees of freedom, rotational states of the vibrational ground state of the trans nitrous acid (HONO) are also investigated.

  8. Variational Calculations of Ro-Vibrational Energy Levels and Transition Intensities for Tetratomic Molecules

    NASA Technical Reports Server (NTRS)

    Schwenke, David W.; Langhoff, Stephen R. (Technical Monitor)

    1995-01-01

    A description is given of an algorithm for computing ro-vibrational energy levels for tetratomic molecules. The expressions required for evaluating transition intensities are also given. The variational principle is used to determine the energy levels and the kinetic energy operator is simple and evaluated exactly. The computational procedure is split up into the determination of one dimensional radial basis functions, the computation of a contracted rotational-bending basis, followed by a final variational step coupling all degrees of freedom. An angular basis is proposed whereby the rotational-bending contraction takes place in three steps. Angular matrix elements of the potential are evaluated by expansion in terms of a suitable basis and the angular integrals are given in a factorized form which simplifies their evaluation. The basis functions in the final variational step have the full permutation symmetries of the identical particles. Sample results are given for HCCH and BH3.

  9. Gmat. A software tool for the computation of the rovibrational G matrix

    NASA Astrophysics Data System (ADS)

    Castro, M. E.; Niño, A.; Muñoz-Caro, C.

    2009-07-01

    Gmat is a C++ program able to compute the rovibrational G matrix in molecules of arbitrary size. This allows the building of arbitrary rovibrational Hamiltonians. In particular, the program is designed to work with the structural results of potential energy hypersurface mappings computed in computer clusters or computational Grid environments. In the present version, 1.0, the program uses internal coordinates as vibrational coordinates, with the principal axes of inertia as body-fixed system. The main design implements a complete separation of the interface and functional parts of the program. The interface part permits the automatic reading of the molecular structures from the output files of different electronic structure codes. At present, Gamess and Gaussian output files are allowed. To such an end, use is made of the object orientation polymorphism characteristic. The functional part computes numerically the derivatives of the nuclear positions respect to the vibrational coordinates. Very accurate derivatives are obtained by using central differences embedded in a nine levels Richardson extrapolation procedure. Program summaryProgram title: Gmat Catalogue identifier: AECZ_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AECZ_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 17 023 No. of bytes in distributed program, including test data, etc.: 274 714 Distribution format: tar.gz Programming language: Standard C++ Computer: All running Linux/Windows Operating system: Linux, Windows Classification: 16.2 Nature of problem: Computation of the rovibrational G matrix in molecules of any size. This allows the building of arbitrary rovibrational Hamiltonians. It must be possible to obtain the input data from the output files of standard electronic structure codes

  10. Leading order nonadiabatic corrections to rovibrational levels of H2, D2, and T2

    NASA Astrophysics Data System (ADS)

    Pachucki, Krzysztof; Komasa, Jacek

    2015-07-01

    An efficient computational approach to nonadiabatic effects in the hydrogen molecule (H2, D2, and T2) is presented. The electronic wave function is expanded in the James-Coolidge basis set, which enables obtaining a very high accuracy of nonadiabatic potentials. A single point convergence of the potentials with growing size of the basis set reveals a relative accuracy ranging from 10-8 to 10-13. An estimated accuracy of the leading nonadiabatic correction to the rovibrational energy levels is of the order of 10-7 cm-1. After a significant increase in the accuracy of the Born-Oppenheimer and adiabatic calculations, the nonadiabatic results presented in this report constitute another step towards highly accurate theoretical description of the hydrogen molecule.

  11. Ro-vibrational averaging of the isotropic hyperfine coupling constant for the methyl radical

    SciTech Connect

    Adam, Ahmad Y.; Jensen, Per; Yachmenev, Andrey; Yurchenko, Sergei N.

    2015-12-28

    We present the first variational calculation of the isotropic hyperfine coupling constant of the carbon-13 atom in the CH{sub 3} radical for temperatures T = 0, 96, and 300 K. It is based on a newly calculated high level ab initio potential energy surface and hyperfine coupling constant surface of CH{sub 3} in the ground electronic state. The ro-vibrational energy levels, expectation values for the coupling constant, and its temperature dependence were calculated variationally by using the methods implemented in the computer program TROVE. Vibrational energies and vibrational and temperature effects for coupling constant are found to be in very good agreement with the available experimental data. We found, in agreement with previous studies, that the vibrational effects constitute about 44% of the constant’s equilibrium value, originating mainly from the large amplitude out-of-plane bending motion and that the temperature effects play a minor role.

  12. Calculation of converged rovibrational energies and partition function for methane using vibrational-rotational configuration interaction.

    PubMed

    Chakraborty, Arindam; Truhlar, Donald G; Bowman, Joel M; Carter, Stuart

    2004-08-01

    The rovibration partition function of CH4 was calculated in the temperature range of 100-1000 K using well-converged energy levels that were calculated by vibrational-rotational configuration interaction using the Watson Hamiltonian for total angular momenta J = 0-50 and the MULTIMODE computer program. The configuration state functions are products of ground-state occupied and virtual modals obtained using the vibrational self-consistent field method. The Gilbert and Jordan potential energy surface was used for the calculations. The resulting partition function was used to test the harmonic oscillator approximation and the separable-rotation approximation. The harmonic oscillator, rigid-rotator approximation is in error by a factor of 2.3 at 300 K, but we also propose a separable-rotation approximation that is accurate within 2% from 100 to 1000 K. PMID:15260761

  13. Ro-vibrational averaging of the isotropic hyperfine coupling constant for the methyl radical.

    PubMed

    Adam, Ahmad Y; Yachmenev, Andrey; Yurchenko, Sergei N; Jensen, Per

    2015-12-28

    We present the first variational calculation of the isotropic hyperfine coupling constant of the carbon-13 atom in the CH3 radical for temperatures T = 0, 96, and 300 K. It is based on a newly calculated high level ab initio potential energy surface and hyperfine coupling constant surface of CH3 in the ground electronic state. The ro-vibrational energy levels, expectation values for the coupling constant, and its temperature dependence were calculated variationally by using the methods implemented in the computer program TROVE. Vibrational energies and vibrational and temperature effects for coupling constant are found to be in very good agreement with the available experimental data. We found, in agreement with previous studies, that the vibrational effects constitute about 44% of the constant's equilibrium value, originating mainly from the large amplitude out-of-plane bending motion and that the temperature effects play a minor role. PMID:26723670

  14. Ro-vibrational averaging of the isotropic hyperfine coupling constant for the methyl radical

    NASA Astrophysics Data System (ADS)

    Adam, Ahmad Y.; Yachmenev, Andrey; Yurchenko, Sergei N.; Jensen, Per

    2015-12-01

    We present the first variational calculation of the isotropic hyperfine coupling constant of the carbon-13 atom in the CH3 radical for temperatures T = 0, 96, and 300 K. It is based on a newly calculated high level ab initio potential energy surface and hyperfine coupling constant surface of CH3 in the ground electronic state. The ro-vibrational energy levels, expectation values for the coupling constant, and its temperature dependence were calculated variationally by using the methods implemented in the computer program TROVE. Vibrational energies and vibrational and temperature effects for coupling constant are found to be in very good agreement with the available experimental data. We found, in agreement with previous studies, that the vibrational effects constitute about 44% of the constant's equilibrium value, originating mainly from the large amplitude out-of-plane bending motion and that the temperature effects play a minor role.

  15. Rovibrational energy levels of hydrogen peroxide, studied by MULTIMODE with a reaction path Hamiltonian.

    PubMed

    Carter, S; Handy, N C

    2004-07-01

    Recently, Carter and Handy [J. Chem. Phys. 113 (2000) 987] have introduced the theory of the reaction path Hamiltonian (RPH) [J. Chem. Phys. 72 (1980) 99] into the variational scheme MULTIMODE, for the calculation of the J=0 vibrational levels of polyatomic molecules, which have a single large-amplitude motion. In this theory the reaction path coordinate s becomes the fourth dimension of the moment-of-inertia tensor, and must be treated separately from the remaining 3N-7 normal coordinates in the MULTIMODE program. In the modified program, complete integration is performed over s, and the M-mode MULTIMODE coupling approximation for the evaluation of the matrix elements applies only to the 3N-7 normal coordinates. In this paper the new algorithm is extended to the calculation of rotational-vibration energy levels (i.e. J>0) with the RPH, following from our analogous implementation for rigid molecules [Theoret. Chem. Acc. 100 (1998) 191]. The full theory is given, and all extra terms have been included to give the exact kinetic energy operator. In order to validate the new code, we report studies on hydrogen peroxide (H2O2), where the reaction path is equivalent to torsional motion. H2O2 has previously been studied variationally using a valence coordinate Hamiltonian; complete agreement for calculated rovibrational levels is obtained between the previous results and those from the new code, using the identical potential surface. MULTIMODE is now able to calculate rovibrational levels for polyatomic molecules which have one large-amplitude motion. PMID:15248993

  16. Rovibrational spectra of ammonia. I. Unprecedented accuracy of a potential energy surface used with nonadiabatic corrections.

    PubMed

    Huang, Xinchuan; Schwenke, David W; Lee, Timothy J

    2011-01-28

    In this work, we build upon our previous work on the theoretical spectroscopy of ammonia, NH(3). Compared to our 2008 study, we include more physics in our rovibrational calculations and more experimental data in the refinement procedure, and these enable us to produce a potential energy surface (PES) of unprecedented accuracy. We call this the HSL-2 PES. The additional physics we include is a second-order correction for the breakdown of the Born-Oppenheimer approximation, and we find it to be critical for improved results. By including experimental data for higher rotational levels in the refinement procedure, we were able to greatly reduce our systematic errors for the rotational dependence of our predictions. These additions together lead to a significantly improved total angular momentum (J) dependence in our computed rovibrational energies. The root-mean-square error between our predictions using the HSL-2 PES and the reliable energy levels from the HITRAN database for J = 0-6 and J = 7∕8 for (14)NH(3) is only 0.015 cm(-1) and 0.020∕0.023 cm(-1), respectively. The root-mean-square errors for the characteristic inversion splittings are approximately 1∕3 smaller than those for energy levels. The root-mean-square error for the 6002 J = 0-8 transition energies is 0.020 cm(-1). Overall, for J = 0-8, the spectroscopic data computed with HSL-2 is roughly an order of magnitude more accurate relative to our previous best ammonia PES (denoted HSL-1). These impressive numbers are eclipsed only by the root-mean-square error between our predictions for purely rotational transition energies of (15)NH(3) and the highly accurate Cologne database (CDMS): 0.00034 cm(-1) (10 MHz), in other words, 2 orders of magnitude smaller. In addition, we identify a deficiency in the (15)NH(3) energy levels determined from a model of the experimental data. PMID:21280738

  17. High-power electron beam tests of a liquid-lithium target and characterization study of (7)Li(p,n) near-threshold neutrons for accelerator-based boron neutron capture therapy.

    PubMed

    Halfon, S; Paul, M; Arenshtam, A; Berkovits, D; Cohen, D; Eliyahu, I; Kijel, D; Mardor, I; Silverman, I

    2014-06-01

    A compact Liquid-Lithium Target (LiLiT) was built and tested with a high-power electron gun at Soreq Nuclear Research Center (SNRC). The target is intended to demonstrate liquid-lithium target capabilities to constitute an accelerator-based intense neutron source for Boron Neutron Capture Therapy (BNCT) in hospitals. The lithium target will produce neutrons through the (7)Li(p,n)(7)Be reaction and it will overcome the major problem of removing the thermal power >5kW generated by high-intensity proton beams, necessary for sufficient therapeutic neutron flux. In preliminary experiments liquid lithium was flown through the target loop and generated a stable jet on the concave supporting wall. Electron beam irradiation demonstrated that the liquid-lithium target can dissipate electron power densities of more than 4kW/cm(2) and volumetric power density around 2MW/cm(3) at a lithium flow of ~4m/s, while maintaining stable temperature and vacuum conditions. These power densities correspond to a narrow (σ=~2mm) 1.91MeV, 3mA proton beam. A high-intensity proton beam irradiation (1.91-2.5MeV, 2mA) is being commissioned at the SARAF (Soreq Applied Research Accelerator Facility) superconducting linear accelerator. In order to determine the conditions of LiLiT proton irradiation for BNCT and to tailor the neutron energy spectrum, a characterization of near threshold (~1.91MeV) (7)Li(p,n) neutrons is in progress based on Monte-Carlo (MCNP and Geant4) simulation and on low-intensity experiments with solid LiF targets. In-phantom dosimetry measurements are performed using special designed dosimeters based on CR-39 track detectors. PMID:24387907

  18. Resolving shocked and UV excited components of H2 emission in planetary nebulae with high-resolution near-infrared spectroscopy

    NASA Astrophysics Data System (ADS)

    Kaplan, Kyle; Dinerstein, Harriet L.; Jaffe, Daniel Thomas

    2016-06-01

    Planetary nebulae (PNe) form when low and intermediate-mass stars eject their outer layers into the ISM at the end of the AGB phase. Many PNe exhibit near-infrared (NIR) emission from molecular hydrogen (H2). This NIR emission arises from radiative decay out of excited rotation-vibration (rovibrational) states. The rovibrational states can be populated by excitation to higher electronic states through absorption of a far-UV photon followed by a radiative cascade to the electronic ground state, or by collisions (e.g., in a hot gas). The two processes populate the rovibrational levels of H2 differently, so the observed emergent emission spectrum provides an effective probe of the mechanisms that excite the H2. Many PNe display line intensity ratios that are intermediate between these two processes (Otsuka et al. 2013). With the advantages of the high spectral resolution (R~40000), broad wavelength coverage (1.45-2.45 μm), and high spatial resolution of the Immersion GRating Infrared Spectrometer (IGRINS, Park et al. 2014), we are able to differentiate components in position-velocity space: we see a slowly expanding UV-excited H2 shell in the PN M 1-11 and two faster moving “bullets” of thermalized H2 that we interpret as shocked gas from a bipolar outflow. We also present observations of several other PNe that exhibit similar morphologies of thermalized and UV-excited H2 components.

  19. Rovibrational states of ClHCl- isotopologues up to high J: a joint theoretical and spectroscopic investigation.

    PubMed

    Sebald, Peter; Oswald, Rainer; Botschwina, Peter; Kawaguchi, Kentarou

    2013-05-14

    Explicitly correlated coupled cluster theory at the CCSD(T*)-F12b level (T. B. Adler, G. Knizia, and H.-J. Werner, J. Chem. Phys., 2007, 127, 221106) and two precise spectroscopic parameters (K. Kawaguchi, J. Chem. Phys., 1988, 88, 4186) were used to construct an accurate near-equilibrium analytical potential energy function (PEF) for the highly anharmonic centrosymmetric hydrogen-bonded complex ClHCl(-) (Re = 3.1153 Å). From variational calculations with that PEF, a large number of rovibrational energies of different isotopologues up to high values of the rotational quantum number J was obtained. Theory helped with the assignment of lines observed by IR diode laser spectroscopy in the ν1 + ν3 combination band of (35)ClH(35)Cl(-) and (37)ClH(35)Cl(-) and enabled us to elucidate rather subtle patterns of rovibrational interactions. Furthermore, transition dipole moments were predicted and analysed as well as unusual isotopic effects. PMID:23549111

  20. A proposed new diagnostic for Herbig disc geometry. FWHM versus J of CO ro-vibrational lines

    NASA Astrophysics Data System (ADS)

    Hein Bertelsen, R. P.; Kamp, I.; van der Plas, G.; van den Ancker, M. E.; Waters, L. B. F. M.; Thi, W.-F.; Woitke, P.

    2016-05-01

    Aims: The CO ro-vibrational lines observed from Herbig group II discs are often seen to be broad, while the same lines observed from group I discs are often narrow. This difference is not well understood. In this paper we explore the underlying cause for this difference and provide a pathway for a better understanding of the geometry and structure of the inner discs around Herbig Ae/Be stars. Methods: High spectral resolution infrared spectra of CO ro-vibrational emission from six Herbig Ae/Be candidate stars were taken with the CRyogenic high-resolution InfraRed Echelle Spectrograph (CRIRES) at the Very Large Telescope (VLT). From these spectra, we produce individual and co-added CO ro-vibrational line profiles. We investigate line profile shape differences, and we explore the full width at half maximum (FWHM) variations with J quantum number in the context of disc geometry. Furthermore, we put our new sources into the context of earlier observed sources to study a large sample. For comparison, we also investigate the FWHM variations with J of modelled CO ro-vibrational lines from two typical disc geometries produced with the thermochemical disc modelling code ProDiMo. Results: For our new observations of CO ro-vibrational lines, we find that the FWHM of individual lines are in the range of 10-60 km s-1. We find both narrow and broad single-peaked emission lines, but only Hen 2-80 displays double-peaked emission lines. For HD 250550, the FWHM of the CO lines increases with J value, indicating a radially extended emitting region, while Hen 2-80 shows a constant FWHM versus J behaviour, indicating a narrow emitting region. This qualitatively agrees with the two different modelled disc geometries. Comparing dust and gas inner disc geometries (inferred by the spectral energy distribution (SED) and CO ro-vibrational emission) for the expanded sample of observed Herbig discs, we find no clear correspondence between the SED (spectral energy distribution) groups of the

  1. Quantum chemical rovibrational data for the interstellar detection of c-C{sub 3}H{sup -}

    SciTech Connect

    Fortenberry, Ryan C.; Huang, Xinchuan; Crawford, T. Daniel; Lee, Timothy J. E-mail: Timothy.J.Lee@nasa.gov

    2014-12-01

    The anion chemistry of the interstellar medium (ISM) has almost exclusively been limited to linear hydrocarbons and cyanocarbons. Of the hydrocarbons, only the even n C {sub n}H{sup –} chains have been detected in the ISM, and lines hypothesized to originate with b-C{sub 3}H{sup –} have been conclusively linked to the corresponding cation, as originally claimed. However, no reason has yet been provided as to why other anions cannot form, and the cyclic form of C{sub 3}H{sup –} is actually the lowest-energy isomer on the anion's potential energy surface. As such, this work provides the necessary rovibrational reference data for the potential detection of this anion in the ISM or related laboratory experiments. Improvements over previously calculated rovibrational spectroscopic constants are contained herein along with graphical depictions of the pure rotational spectra at 100 K, 40 K, 20 K, and 2.7 K.

  2. Note: Improved line strengths of rovibrational and rotational transitions within the X3Σ- ground state of NH

    NASA Astrophysics Data System (ADS)

    Brooke, James S. A.; Bernath, Peter F.; Western, Colin M.

    2015-07-01

    Recently, a line list including positions and transition strengths was published for the NH X3Σ- rovibrational and rotational transitions. The calculation of the transition strengths requires a conversion of transition matrix elements from Hund's case (b) to (a). The method of this conversion has recently been improved during other work on the OH X2Π rovibrational transitions, by removing an approximation that was present previously. The adjusted method has been applied to the NH line list, resulting in more accurate transition strengths. An updated line list is presented that contains all possible transitions with v' and v″ up to 6, and J up to between 25 and 44, depending on the band.

  3. Modelling rotations, vibrations, and rovibrational couplings in astructural molecules - a case study based on the H+5 molecular ion

    NASA Astrophysics Data System (ADS)

    Sarka, János; Fábri, Csaba; Szidarovszky, Tamás; Császár, Attila G.; Lin, Zhou; McCoy, Anne B.

    2015-07-01

    One-dimensional (1D) and two-dimensional (2D) models are investigated, which help to understand the unusual rovibrational energy-level structure of the astronomically relevant and chemically interesting astructural molecular ion H+5. Due to the very low hindering barrier characterising the 1D torsion-only vibrational model of H+5, this model yields strongly divergent energy levels. The results obtained using a realistic model for the torsion potential, including the computed (near) degeneracies, can be rationalised in terms of the model with no barrier. Coupling of the torsional motion with a single rotational degree of freedom is also investigated in detail. It is shown how the embedding-dependent rovibrational models yield energy levels that can be rationalised via the 2D vibrational model containing two independent torsions. Insight into the complex rovibrational energy level structure of the models and of H+5 is gained via variational nuclear motion and diffusion Monte Carlo computations and by the analysis of the wavefunctions they provide. The modelling results describing the transition from the zero barrier limit to the large barrier limit should prove to be useful for the important class of molecules and molecular ions that contain two weakly coupled internal rotors.

  4. The Cologne Carbon Cluster Experiment: ro-vibrational spectroscopy on C 8 and other small carbon clusters

    NASA Astrophysics Data System (ADS)

    Neubauer-Guenther, P.; Giesen, T. F.; Berndt, U.; Fuchs, G.; Winnewisser, G.

    2003-02-01

    We report on our ongoing efforts in obtaining the IR-spectra of the linear carbon cluster molecules C n with n=8-13. So far C 8, C 9, C 10, and C 13 have been recorded at Cologne. With the exception of C 8 all assignments have been secured. For C 8 a tentative assignment could be derived with the bandcenter of the σu antisymmetric stretching mode located at ν0=2067.9779 cm -1 and a preliminary rotational constant in the vibrational ground state of B″=0.02068 cm -1. The measured signal to noise ratio of the ro-vibrational band is fairly weak and thus the lower J ro-vibrational transitions can not be assigned with certainty. As a consequence the band center remains uncertain by 4 J or 0.17 cm -1. For a more reliable assignment the sensitivity of the system has to be increased by at least one order of magnitude. The envisaged sensitivity increase of our experiment will be discussed along with the intention to perform terahertz observations of the low energetic bending ro-vibrational spectra. These sub-mm wave measurements will be carried out simultaneously with the IR measurements.

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

    SciTech Connect

    Zatsarinny, O.; Tayal, S. S.

    2010-04-15

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

  6. Rotational and rovibrational spectrum of C 15NC 15N in the region of the bending modes ν4, ν5, the combination band ν4 + ν5 and the Fermi interacting modes ν3, 2 ν4

    NASA Astrophysics Data System (ADS)

    Seibert, J. W. Günter; Winnewisser, Manfred; Winnewisser, Brenda P.; Bickelhaupt, Friedrich

    1996-02-01

    The high-resolution gas-phase Fourier transform infrared spectrum of the doubly 15N-substituted isocyanogen, C 15NC 15N, has been measured in the spectral regions 160-240 cm -1 and 390-1110 cm -1 with unapodized resolutions of 0.0017 and 0.0021 cm -1 respectively. In these experiments we were able to measure the band systems due to the excitation of the bending modes ν5 and ν4 at 190.9 cm -1 and 458.1 cm -1, a combination band system of the two bending modes ν4 + ν5 at 649.7 cm -1, as well as two band systems arising from a Fermi interaction between the twofold excited bending mode 2 ν4 and the stretching mode ν3 at 869.9 cm -1 and 960.2 cm -1 respectively. Furthermore, we have measured and assigned pure rotational transitions of C 15NC 15N in the vibrational ground state and in excited vibrational bending states lying in the microwave and the millimeter wave region between 19.9 and 20.2 GHz, 29.9 and 30.4 GHz and 120 and 440 GHz. Constants of a power series in J( J + 1) for numerous rovibrational subbands, as well as accurate molecular constants using the effective hamiltonian for linear polyatomic molecules, defined by Yamada et al. [J. Mol. Spectrosc., 112 (1985) 347], were determined.

  7. Model for the hyperfine structure of electronically excited KCs molecules

    NASA Astrophysics Data System (ADS)

    Orbán, A.; Vexiau, R.; Krieglsteiner, O.; Nägerl, H.-C.; Dulieu, O.; Crubellier, A.; Bouloufa-Maafa, N.

    2015-09-01

    A model for determining the hyperfine structure of the excited electronic states of diatomic bialkali heteronuclear molecules is formulated from the atomic hyperfine interactions and is applied to the case of bosonic 39KCs and fermionic 40KCs molecules. The hyperfine structure of the potential-energy curves of the states correlated to the K (4 s 2S1 /2) +Cs (6 p 2P1 /2 ,3 /2) dissociation limits is described in terms of different coupling schemes depending on the internuclear distance R . These results provide a step in the calculation of the hyperfine structure of rovibrational levels of these excited molecular states in the perspective of the identification of efficient paths for creating ultracold ground-state KCs molecules.

  8. Line strengths of rovibrational and rotational transitions within the X^3Σ {^-} ground state of NH

    NASA Astrophysics Data System (ADS)

    Brooke, James S. A.; Bernath, Peter F.; Western, Colin M.; van Hemert, Marc C.; Groenenboom, Gerrit C.

    2014-08-01

    A new line list for rovibrational and rotational transitions, including fine structure, within the NH X^3Σ {^-} ground state has been created. It contains line intensities in the form of Einstein A and f-values, for all possible bands up to v' = 6, and for J up to between 25 and 44. The intensities are based on a new dipole moment function (DMF), which has been calculated using the internally contracted multi-reference configuration interaction method with an aug-cc-pV6Z basis set. The programs RKR1, LEVEL, and PGOPHER were used to calculate line positions and intensities using the most recent spectroscopic line position observations and the new DMF, including the rotational dependence on the matrix elements. The Hund's case (b) matrix elements from the LEVEL output (available as Supplement 1 of the supplementary material) have been transformed to the case (a) form required by PGOPHER. New relative intensities for the (1,0) band have been measured, and the calculated and observed Herman-Wallis effects are compared, showing good agreement. The line list (see Supplement 5 of the supplementary material) will be useful for the study of NH in astronomy, cold and ultracold molecular systems, and in the nitrogen chemistry of combustion.

  9. Rovibrational molecular populations, atoms, and negative ions in H2 and D2 magnetic multicusp discharges

    NASA Astrophysics Data System (ADS)

    Pealat, M.; Taran, J.-P. E.; Bacal, M.; Hillion, F.

    1985-06-01

    Coherent anti-Stokes Raman scattering is applied to the study of rovibrational populations in magnetic multicusp H2 and D2 discharges. This subject is of interest to negative hydrogen-ion formation by volume plasma processes. The populations of high-lying rotational states (J greater than 5) in the vibrational levels v = 0, 1, and 2 are found to be significantly higher than expected from the Boltzmann law. In H2 the net populations of the first four vibrational levels follow approximately the Boltzmann law, with the vibrational temperature of 2390 K (in a 90 V-10 A discharge at 55 micro bar). In similar discharge conditions, the population of the state v = 3 in D2 is higher than expected from the Boltzmann law. In the presence of the discharge a deficiency in H2 and D2 molecule density was observed and was attributed to the possible presence of H and D atoms. This was verified by an independent measurement of the atomic fraction and temperature. The density of negative ions, measured by the photodetachment technique, is also reported.

  10. High-Accuracy Predictions of Rovibrational Transitions for Small Molecules in Titan's Atmosphere

    NASA Astrophysics Data System (ADS)

    Fortenberry, R. C.; Huang, X.; Lee, T. J.

    2012-12-01

    Using highly accurate quantum chemical techniques, we are predicting rotational constants, vibrational frequencies, and other spectroscopic constants of the first triplet states of hydrogen cyanide (HCN) and the isoelectronic HCO+. The ground-state singlet rovibrational data has been well-documented for these systems, but with all of the photochemistry present in Titan's atmosphere, it is necessary to examine the first triplet state of these simple systems. Furthermore, Voyager 1 detected HCN in Titan's atmosphere, and it has been hypothesized that HCO+, or related systems, may be present, as well. Our approach is based on a quartic force field defined from points computed at the coupled cluster level of quantum chemical theory extrapolated out to the complete basis set limit further corrected to include effects from core correlation and relativity. This technique is known to give accuracies to within less than 1% error in the prediction of rotational constants and often accurate to within 1 cm-1 in the prediction of vibrational frequencies for various test cases. Accurate reference data is necessary for the detection of molecules in Titan's atmosphere at mid-infrared, far-infrared, and sub-millimeter wavelengths, and we are providing new information on these "old" systems.

  11. A Study of ro-vibrational OH Emission from Herbig Ae/Be Stars

    NASA Astrophysics Data System (ADS)

    Brittain, Sean D.; Adamkovics, Mate; Carr, John S.; Najita, Joan R.

    2016-06-01

    We present a study of ro-vibrational OH and CO emission from 21 disks around Herbig Ae/Be stars. We find that the luminosity of the OH emission is proportional to the luminosity of the CO emission over five orders of magnitude in stellar ultraviolet luminosity. We also find that the profiles of the OH and CO emission lines are similar indicating that they arise from the same radial region of the disk.The CO and OH emission are both correlated with the far ultraviolet (1300-1840Å) luminosity of the stars while the luminosity of the PAH emission is correlated with the longer wavelength ultraviolet (2450-3200Å) luminosity of the stars. Our interpretation of the observations is that the OH and CO are heated by ultraviolet photons in the same region of the disk. We also find that while disk flaring affects the PAH luminosity, it is not a factor in the luminosity of the OH and CO emission. However, transition disks with large inner holes do have systematically lower OH and CO luminosities.

  12. Rovibrational analysis of the ν4 and ν5+ ν9 bands of CHCl 2F

    NASA Astrophysics Data System (ADS)

    Albert, Sieghard; Keppler Albert, Karen; Quack, Martin

    2004-06-01

    The infrared spectrum of CHCl 2F has been measured with a new, very high resolution Fourier transform infrared spectrometer, the Bruker IFS 120 HR Zürich Prototype (ZP) 2001. The spectrum was recorded with a resolution of 0.0007 cm -1 in the range 600-2300 cm -1 at room temperature. The assignment of the rovibrational transitions has been carried out with the Giessen interactive Loomis-Wood program developed by Winnewisser et al. [J. Mol. Spectrosc. 136 (1989) 12] and the least squares adjustment has been performed with the Zürich WANG program. The spectrum has been analyzed in the ν4 region of CH 35Cl 2F ( ν˜0=744.474 cm-1) and the ν5+ ν9 regions of CH 35Cl 2F ( ν˜0=829.084 cm-1) and CH 35Cl 37ClF ( ν˜0=825.027 cm-1) using an effective Hamiltonian. Both bands are important to understand the absorption behavior of the fluorochlorohydrocarbon CHCl 2F, important in the context of atmospheric pollution as well as in laser chemistry. Local perturbations have been identified in both bands. The results are discussed in relation to molecular parity violation in the case of the chiral isotopomer CH 35Cl 37ClF.

  13. Line strengths of rovibrational and rotational transitions in the X2 Π ground state of OH

    NASA Astrophysics Data System (ADS)

    Brooke, James S. A.; Bernath, Peter F.; Western, Colin M.; Sneden, Christopher; Afşar, Melike; Li, Gang; Gordon, Iouli E.

    2016-01-01

    A new line list including positions and absolute transition strengths (in the form of Einstein A values and oscillator strengths) has been produced for the OH ground X2 Π state rovibrational (Meinel system) and pure rotational transitions. All possible transitions are included with v‧ and v ″ up to 13, and J up to between 9.5 and 59.5, depending on the band. An updated fit to determine molecular constants has been performed, which includes some new rotational data and a simultaneous fitting of all molecular constants. The absolute transition strengths are based on a new dipole moment function, which is a combination of two high level ab initio calculations. The calculations show good agreement with an experimental v = 1 lifetime, experimental μv values, and Δv=2 line intensity ratios from an observed spectrum. To achieve this good agreement, an alteration in the method of converting matrix elements from Hund's case (b) to (a) was made. Partitions sums have been calculated using the new energy levels, for the temperature range 5-6000 K, which extends the previously available (in HITRAN) 70-3000 K range. The resulting absolute transition strengths have been used to calculate O abundances in the Sun, Arcturus, and two red giants in the Galactic open and globular clusters M67 and M71. Literature data based mainly on [O I] lines are available for the Sun and Arcturus, and excellent agreement is found.

  14. High-level theoretical rovibrational spectroscopy beyond fc-CCSD(T): The C3 molecule

    NASA Astrophysics Data System (ADS)

    Schröder, Benjamin; Sebald, Peter

    2016-01-01

    An accurate local (near-equilibrium) potential energy surface (PES) is reported for the C3 molecule in its electronic ground state ( X ˜ 1 Σg + ). Special care has been taken in the convergence of the potential relative to high-order correlation effects, core-valence correlation, basis set size, and scalar relativity. Based on the aforementioned PES, several rovibrational states of all 12C and 13C substituted isotopologues have been investigated, and spectroscopic parameters based on term energies up to J = 30 have been calculated. Available experimental vibrational term energies are reproduced to better than 1 cm-1 and rotational constants show relative errors of not more than 0.01%. The equilibrium bond length has been determined in a mixed experimental/theoretical approach to be 1.294 07(10) Å in excellent agreement with the ab initio composite value of 1.293 97 Å. Theoretical band intensities based on a newly developed electric dipole moment function also suggest that the infrared active (1, 11, 0)←(0, 00, 0) combination band might be observable by high-resolution spectroscopy.

  15. High-level theoretical rovibrational spectroscopy beyond fc-CCSD(T): The C3 molecule.

    PubMed

    Schröder, Benjamin; Sebald, Peter

    2016-01-28

    An accurate local (near-equilibrium) potential energy surface (PES) is reported for the C3 molecule in its electronic ground state (X̃(1)Σg (+)). Special care has been taken in the convergence of the potential relative to high-order correlation effects, core-valence correlation, basis set size, and scalar relativity. Based on the aforementioned PES, several rovibrational states of all (12)C and (13)C substituted isotopologues have been investigated, and spectroscopic parameters based on term energies up to J = 30 have been calculated. Available experimental vibrational term energies are reproduced to better than 1 cm(-1) and rotational constants show relative errors of not more than 0.01%. The equilibrium bond length has been determined in a mixed experimental/theoretical approach to be 1.294 07(10) Å in excellent agreement with the ab initio composite value of 1.293 97 Å. Theoretical band intensities based on a newly developed electric dipole moment function also suggest that the infrared active (1, 1(1), 0)←(0, 0(0), 0) combination band might be observable by high-resolution spectroscopy. PMID:26827217

  16. VIBRATIONALLY EXCITED HCN AROUND AFGL 2591: A PROBE OF PROTOSTELLAR STRUCTURE

    SciTech Connect

    Veach, Todd J.; Groppi, Christopher E.; Hedden, Abigail

    2013-03-10

    Vibrationally excited molecules with submillimeter rotational transitions are potentially excellent probes of physical conditions near protostars. This study uses observations of the v = 1 and v = 2 ro-vibrational modes of HCN (4-3) to probe this environment. The presence or absence and relative strengths of these ro-vibrational lines probe the gas excitation mechanism and physical conditions in warm, dense material associated with protostellar disks. We present pilot observations from the Heinrich Hertz Submillimeter Telescope and follow-up observations from the Submillimeter Array. All vibrationally excited HCN (4-3) v = 0, v = 1, and v = 2 lines were observed. The existence of the three v = 2 lines at approximately equal intensity imply collisional excitation with a density of greater than (10{sup 10} cm{sup -3}) and a temperature of >1000 K for the emitting gas. This warm, high-density material should directly trace structures formed in the protostellar envelope and disk environment. Further, the line shapes of the v = 2 emission may suggest a Keplerian disk. This Letter demonstrates the utility of this technique which is of particular interest due to the recent inauguration of the Atacama Large Millimeter Array.

  17. Influence of the Reactants Rotational Excitation on the H+D2(v=0, j) Reactivity

    PubMed Central

    Aldegunde, J; Jambrina, PG; González-Sanchez, L; Herrero, VJ; Aoiz, FJ

    2016-01-01

    We have analyzed the influence of the rotational excitation on the H+D2(υ=0, j) reaction through quantum mechanical (QM) and quasiclassical trajectories (QCT) calculations at a wide range of total energies. The agreement between both types of calculations is excellent. We have found that the rotational excitation largely increases the reactivity at large values of the total energy. Such increase cannot be attributed to a stereodynamical effect but to the existence of recrossing trajectories that become reactive as the target molecule gets rotationally excited. At low total energies, however, recrossing is not significant and the reactivity evolution is dominated by changes in the collision energy; the reactivity decreases with the collision energy as it shrinks the acceptance cone. When state-to-state results are considered, rotational excitation leads to cold product’s rovibrational distributions, so that most of the energy is released as recoil energy. PMID:26305719

  18. Influence of the Reactants Rotational Excitation on the H + D2(v = 0, j) Reactivity.

    PubMed

    Aldegunde, J; Jambrina, P G; González-Sanchez, L; Herrero, V J; Aoiz, F J

    2015-12-17

    We have analyzed the influence of the rotational excitation on the H + D2(v = 0, j) reaction through quantum mechanical (QM) and quasiclassical trajectories (QCT) calculations at a wide range of total energies. The agreement between both types of calculations is excellent. We have found that the rotational excitation largely increases the reactivity at large values of the total energy. Such an increase cannot be attributed to a stereodynamical effect but to the existence of recrossing trajectories that become reactive as the target molecule gets rotationally excited. At low total energies, however, recrossing is not significant and the reactivity evolution is dominated by changes in the collision energy; the reactivity decreases with the collision energy as it shrinks the acceptance cone. When state-to-state results are considered, rotational excitation leads to cold product's rovibrational distributions, so that most of the energy is released as recoil energy. PMID:26305719

  19. ATIRS package: A program suite for the rovibrational analysis of infrared spectra of asymmetric top molecules

    NASA Astrophysics Data System (ADS)

    Tasinato, N.; Pietropolli Charmet, A.; Stoppa, P.

    2007-06-01

    Nowadays high-resolution infrared spectra can be recorded quite easily and therefore it has become important to assist the rovibrational analysis, especially the assignment step, that is still fraught with many problems in the presence of perturbation effects. In this article we provide a description of ATIRS, a complete software suite developed for assisting in the rotational investigation of vibrational bands of asymmetric top molecules. This package uses the Pickett's CALPGM suite for fitting transitions and predicting line positions and is composed by three stand-alone applications: (1) Visual Loomis-Wood for the assignment of spectral lines based on Loomis-Wood type diagrams; (2) Visual CALPGM, a new graphical interface to Pickett's programs SPFIT and SPCAT; (3) Visual Spectra Simulator for the simulation of spectra. The graphical interface to the CALPGM suite is developed for asymmetric rotors. The main feature of this application is to avoid the use of the parameter codes that are here replaced employing the well known parameter names or symbols. Highlighting the regular transition sequences, Visual Loomis-Wood assists in the assignment of the spectral lines. It visualizes the description of a transition and the assignment can be simply done by mouse-clicking on the diagram; moreover its display mode feature lets to check the experimental spectrum in which all the assigned lines together with their description are reported. Visual Spectra Simulator provides a simple and functionally application that, using the calculated frequencies and intensities given by SPCAT, simulates the high-resolution infrared spectrum and compare it to the experimental one. ATIRS, freely available to the spectroscopic community, is designed to be easy to use and presents a standard graphical interface; being based on the CALPGM package it can handle forbidden transitions and perturbations among many states.

  20. ON THE ASYMMETRY OF THE OH RO-VIBRATIONAL LINES IN HD 100546

    SciTech Connect

    Fedele, D.; Bruderer, S.; Van den Ancker, M. E.; Pascucci, I. E-mail: mvandena@eso.org

    2015-02-10

    We present multi-epoch high-spectral resolution observations with VLT/CRIRES of the OH doublet {sup 2}Π{sub 3/2} P4.5 (1+, 1–) (2.934 μm) toward the protoplanetary disk around HD 100546. The OH doublet is detected at all epochs and is spectrally resolved while nearby H{sub 2}O lines remain undetected. The OH line velocity profile is different in the three data sets: in the first epoch (2012 April, P.A. = 26°) the OH lines are symmetric and line broadening is consistent with the gas being in Keplerian rotation around the star. No OH emission is detected within a radius of 8-11 AU from the star: the line emitting region is similar in size and extent to that of the CO ro-vibrational lines. In the other two epochs (2013 March and 2014 April, P.A. = 90° and 10°, respectively) the OH lines appear asymmetric and fainter compared to 2012 April. We investigate the origin of these line asymmetries which were taken by previous authors as evidence for tidal interaction between a (unseen) massive planet and the disk. We show that the observed asymmetries can be fully explained by a misalignment of the slit of the order of 0.''04-0.''20 with respect to the stellar position. The disk is spatially resolved and the slit misalignment is likely caused by the extended dust emission which is brighter than the stellar photosphere at near-infrared wavelengths which is the wavelength used for the pointing. This can cause the photo-center of HD 100546 to be misaligned with the stellar position at near-infrared wavelengths.

  1. Optical controling dynamic and fluctuation processes in ensemble of neurons at pulsed electrical excitation ex vivo

    NASA Astrophysics Data System (ADS)

    Akchurin, Garif G.; Seliverstov, George A.; Akchurin, Alexander G.; Akchurin, George G.

    2004-05-01

    Dynamic response of the somatic frog nerve on electrical pulsed excitation was investigated ex vivo. Strong fluctuation of consequence compound action potential in ensemble of neurons near-threshold was discovered. The nonlinear response of the Hodgkin-Huxley model neurons with external electrical pulsed was investigated and numeral results correlation with experiments. Complex dynamic of compound action potential was discovered when on-line time of stimulatory electrical pulses comparable with nerve refractory period. New techniques research nonlinear behavior using photodynamic reactions or UV-A radiation at somatic frog nerve was approved. This nonlinear dynamic regime was controlling laser induced inactivation of processes in membrane of nerve.

  2. Differential excitation spectroscopy for detection of common explosives: ammonium nitrate and urea nitrate

    NASA Astrophysics Data System (ADS)

    Hunter, Boyd V.; Cox, Jason M.; Miller, Michael A.; Hunter, Richard V.; Van Bastian, Levi; Harrison, Paul; Walters, William P.

    2015-05-01

    Differential Excitation Spectroscopy (DES) is a new pump-probe detection technique (patent-pending) which characterizes molecules based on a multi-dimensional parameterization of the rovibrational excited state structure, pump and probe interrogation frequencies, as well as the lifetimes of the excited states. Under appropriate conditions, significant modulation of the ground state can result. DES results provide a unique, simple mechanism to probe various molecules. In addition, the DES multi-dimensional parameterization provides an identification signature that is highly unique and has demonstrated high levels of immunity from interferents, providing significant practical value for high-specificity material identification. Ammonium nitrate (AN) and urea nitrate (UN) are both components commonly used in IEDs; the ability to reliably detect these chemicals is key to finding, identifying and defeating IEDs. AN and UN are complicated materials, having a number of different phases and because they are molecular crystals, there are a number of different types of interactions between the constituent atoms which must be characterized in order to understand their DES behavior. Ab initio calculations were performed on both AN and UN for various rovibrational states up to J' ≤ 3 and validated experimentally, demonstrating good agreement between theory and experiment and the very specific responses generated.

  3. Differential excitation spectroscopy for detection of chemical threats: DMMP and thiodiglycol

    NASA Astrophysics Data System (ADS)

    Hunter, Boyd V.; Cox, Jason M.; Miller, Michael A.; Harrison, Paul; Walters, William P.

    2015-05-01

    Differential Excitation Spectroscopy (DES) is a new pump-probe detection technique (patent-pending) which characterizes molecules based on a multi-dimensional parameterization of the rovibrational excited state structure, pump and probe interrogation frequencies, as well as the lifetimes of the excited states. Under appropriate conditions, significant modulation of the ground state can result. DES results provide a unique, simple mechanism to probe various molecules. In addition, the DES multi-dimensional parameterization provides an identification signature that is highly unique and has demonstrated high levels of immunity from interferents, providing significant practical value for highspecificity material identification. Dimethyl methylphosphonate (DMMP) is used as a simulant for G series nerve agents and thiodiglycol as a simulant for sulfur mustard (HD). Ab initio calculations were performed on DMMP for various rovibrational states up to J' ≤ 3 and validated experimentally, demonstrating good agreement between theory and experiment and the very specific responses generated. Thiodiglycol was investigated empirically. Optimal detection parameters were determined and mixtures of the two materials were used to demonstrate the immunity of the DES technique to interference from other materials, even those whose IR spectra show significant overlap.

  4. HIGH-RESOLUTION NEAR-INFRARED SPECTROSCOPY OF HD 100546. I. ANALYSIS OF ASYMMETRIC RO-VIBRATIONAL OH EMISSION LINES

    SciTech Connect

    Liskowsky, Joseph P.; Brittain, Sean D.; Najita, Joan R.; Carr, John S.; Doppmann, Greg W.; Troutman, Matthew R. E-mail: najita@noao.edu E-mail: gdoppmann@keck.hawaii.edu

    2012-12-01

    We present observations of ro-vibrational OH and CO emission from the Herbig Be star HD 100546. The emission from both molecules arises from the inner region of the disk extending from approximately 13 AU from the central star. The velocity profiles of the OH lines are narrower than the velocity profile of the [O I] {lambda}6300 line, indicating that the OH in the disk is not cospatial with the O I. This suggests that the inner optically thin region of the disk is largely devoid of molecular gas. Unlike the ro-vibrational CO emission lines, the OH lines are highly asymmetric. We show that the average CO and average OH line profiles can be fit with a model of a disk comprised of an eccentric inner wall and a circular outer disk. In this model, the vast majority of the OH flux (75%) originates from the inner wall, while the vast majority of the CO flux (65%) originates on the surface of the disk at radii greater than 13 AU. Eccentric inner disks are predicted by hydrodynamic simulations of circumstellar disks containing an embedded giant planet. We discuss the implications of such a disk geometry in light of models of planet-disk tidal interactions and propose alternative explanations for the origin of the asymmetry.

  5. Communication: The ground electronic state of Si2C: Rovibrational level structure, quantum monodromy, and astrophysical implications

    NASA Astrophysics Data System (ADS)

    Reilly, Neil J.; Changala, P. Bryan; Baraban, Joshua H.; Kokkin, Damian L.; Stanton, John F.; McCarthy, Michael C.

    2015-06-01

    We report the gas-phase optical detection of Si2C near 390 nm and the first experimental investigation of the rovibrational structure of its 1A1 ground electronic state using mass-resolved and fluorescence spectroscopy and variational calculations performed on a high-level ab initio potential. From this joint study, it is possible to assign all observed Ka = 1 vibrational levels up to 3800 cm-1 with confidence, as well as a number of levels in the Ka = 0, 2, and 3 manifolds. Dixon-dip plots for the bending coordinate (ν2) allow an experimental determination of a barrier to linearity of 783(48) cm-1 (2σ), in good agreement with theory (802(9) cm-1). The calculated (Ka, ν2) eigenvalue lattice shows an archetypal example of quantum monodromy (absence of a globally valid set of quantum numbers) that is reflected by the experimentally observed rovibrational levels. The present study provides a solid foundation for infrared and optical surveys of Si2C in astronomical objects, particularly in the photosphere of N- and J-type carbon stars where the isovalent SiC2 molecule is known to be abundant.

  6. Communication: The ground electronic state of Si2C: Rovibrational level structure, quantum monodromy, and astrophysical implications.

    PubMed

    Reilly, Neil J; Changala, P Bryan; Baraban, Joshua H; Kokkin, Damian L; Stanton, John F; McCarthy, Michael C

    2015-06-21

    We report the gas-phase optical detection of Si2C near 390 nm and the first experimental investigation of the rovibrational structure of its (1)A1 ground electronic state using mass-resolved and fluorescence spectroscopy and variational calculations performed on a high-level ab initio potential. From this joint study, it is possible to assign all observed Ka = 1 vibrational levels up to 3800 cm(-1) with confidence, as well as a number of levels in the Ka = 0, 2,  and 3 manifolds. Dixon-dip plots for the bending coordinate (ν2) allow an experimental determination of a barrier to linearity of 783(48) cm(-1) (2σ), in good agreement with theory (802(9) cm(-1)). The calculated (Ka, ν2) eigenvalue lattice shows an archetypal example of quantum monodromy (absence of a globally valid set of quantum numbers) that is reflected by the experimentally observed rovibrational levels. The present study provides a solid foundation for infrared and optical surveys of Si2C in astronomical objects, particularly in the photosphere of N- and J-type carbon stars where the isovalent SiC2 molecule is known to be abundant. PMID:26093543

  7. Communication: The ground electronic state of Si{sub 2}C: Rovibrational level structure, quantum monodromy, and astrophysical implications

    SciTech Connect

    Reilly, Neil J.; Kokkin, Damian L.; McCarthy, Michael C.; Changala, P. Bryan; Baraban, Joshua H.; Stanton, John F.

    2015-06-21

    We report the gas-phase optical detection of Si{sub 2}C near 390 nm and the first experimental investigation of the rovibrational structure of its {sup 1}A{sub 1} ground electronic state using mass-resolved and fluorescence spectroscopy and variational calculations performed on a high-level ab initio potential. From this joint study, it is possible to assign all observed K{sub a} = 1 vibrational levels up to 3800 cm{sup −1} with confidence, as well as a number of levels in the K{sub a} = 0, 2,  and 3 manifolds. Dixon-dip plots for the bending coordinate (ν{sub 2}) allow an experimental determination of a barrier to linearity of 783(48) cm{sup −1} (2σ), in good agreement with theory (802(9) cm{sup −1}). The calculated (K{sub a}, ν{sub 2}) eigenvalue lattice shows an archetypal example of quantum monodromy (absence of a globally valid set of quantum numbers) that is reflected by the experimentally observed rovibrational levels. The present study provides a solid foundation for infrared and optical surveys of Si{sub 2}C in astronomical objects, particularly in the photosphere of N- and J-type carbon stars where the isovalent SiC{sub 2} molecule is known to be abundant.

  8. Photoionization of N2X ¹Σg⁺, v"=0 and 1 near threshold. Preionization of the Worley–Jenkins Rydberg series.

    SciTech Connect

    Dehmer, Patricia M.; Miller, P. J.; Chupka, W. A.

    1984-01-01

    The high resolution relative photoionization cross section for N2 is reported in the wavelength region from the ionization threshold to 650 Â, with particular attention given to the region between the N₂⁺ X ²Σg⁺, v'=0 and 1 ionization limits. Cross sections from both the X ¹Σg⁺, v''=0 and 1 vibrational levels were determined in this region, and preionized members of the n ρπu ¹Πu Worley–Jenkins Rydberg series converging to N₂⁺ X ²Σg⁺, v' = 1 are observed in both spectra. In the spectrum excited from v'' = 1, the Worley–Jenkins series appears prominently as a result of good Franck–Condon overlap between the N₂⁺ X ¹Σg, v"=1 and the N₂⁺ X ²Σg⁺, v'=1 levels; the intensities of the series members decrease approximately as 1/n³, in accord with simple theoretical predictions. However, in the spectrum excited from v''=0, the Worley–Jenkins series converging to N₂⁺ X ²Σg⁺, v'=1 is weak as a result of a poor Franck–Condon overlap with the ground vibrational level; the intensities of the series members show large deviations from the simple theory as a result of channel interactions with Rydberg states converging to N₂ ⁺A ²Πu. These perturbing Rydberg states have low photoabsorptionoscillator strengths for excitation from v"=1 (in contrast to excitation from v"=0) and hence have only a small effect on the cross section from the excited vibrational level. Just as in the case of photoionization of H₂, the results demonstrate that channel interaction can redistribute the oscillator strength of a perturbing Rydberg state of low principal quantum number over a number of members of an interacting Rydberg series and that the spectral range affected by the perturber can be much greater than the width of the perturbing level.

  9. ASPIN: An all spin scattering code for atom molecule rovibrationally inelastic cross sections

    NASA Astrophysics Data System (ADS)

    López-Durán, D.; Bodo, E.; Gianturco, F. A.

    2008-12-01

    We present in this work a new computational code for the quantum calculation of integral cross sections for atom-molecule (linear) scattering processes. The atom is taken to be structureless while the molecule can be in its singlet, doublet, or triplet spin states and can be treated as either a rigid rotor or a rovibrational target. All the relevant state-to-state integral cross sections, and their sums over final states, can be calculated with the present code, for which we also describe in detail the various component routines. Program summaryProgram title: ASPIN Catalogue identifier: AEBO_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEBO_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 99 596 No. of bytes in distributed program, including test data, etc.: 1 267 615 Distribution format: tar.gz Programming language: Fortran/MPI Computer: AMD OPTERON COMPUTING SYSTEMS, model TYAN GX28 (B2882) Operating system: SuSE LINUX Professional 9 RAM: 128 GB Classification: 2.6 External routines: LAPACK/BLAS Nature of problem: Scattering of a diatomic molecule in its Σ1, Σ2, or Σ3 spin states with an atom in its S1 state. Partial and integral cross sections. Solution method: The coupled channel equations that describe the scattering process are solved through the propagation of the reactance K matrix employing a modification of the Variable Phase Method [1-3]. Restrictions: Depending on the vib-rotational base used the problem may or may not fit into available RAM memory because all the runtime relevant quantities are stored on RAM memory instead of on disk. Additional comments: Both serial and parallel implementations of the program are provided. The CPC Librarian was not able to successfully run the parallel version. Running time: For simple and converged

  10. Calculation of antihydrogen formation via antiproton scattering with excited positronium

    NASA Astrophysics Data System (ADS)

    Rawlins, C. M.; Kadyrov, A. S.; Stelbovics, A. T.; Bray, I.; Charlton, M.

    2016-01-01

    The two-center convergent close-coupling method is used to calculate antihydrogen (H ¯) formation via positronium (Ps) scattering on antiprotons (p ¯) at near threshold energies. For excited Ps of energy ɛ , the 1 /ɛ behavior of the H ¯ formation cross sections is valid strictly only at the respective threshold, as is the 1 /√{ɛ } behavior for Ps in the ground state. Simple equations are given for the H ¯(n ≤4 ) formation cross sections from Ps(n ≤3 ) from zero to around 0.1 eV above threshold. Some of the implications of using p ¯-Ps collisions to form antihydrogen in beams, and held in traps, are discussed.

  11. Excited Delirium

    PubMed Central

    Takeuchi, Asia; Ahern, Terence L.; Henderson, Sean O.

    2011-01-01

    Excited (or agitated) delirium is characterized by agitation, aggression, acute distress and sudden death, often in the pre-hospital care setting. It is typically associated with the use of drugs that alter dopamine processing, hyperthermia, and, most notably, sometimes with death of the affected person in the custody of law enforcement. Subjects typically die from cardiopulmonary arrest, although the cause is debated. Unfortunately an adequate treatment plan has yet to be established, in part due to the fact that most patients die before hospital arrival. While there is still much to be discovered about the pathophysiology and treatment, it is hoped that this extensive review will provide both police and medical personnel with the information necessary to recognize and respond appropriately to excited delirium. PMID:21691475

  12. Excited baryons

    SciTech Connect

    Mukhopadhyay, N.C.

    1986-01-01

    The status of the theory of the low-energy approach to hadron structure is reviewed briefly by surveying a few relevant models. A few examples of tests needed to sort out the predictions of different models pertaining to the quark-gluon structure of hadrons are discussed, and given the resulting physics objectives, a few experimental options for excited baryon research at CFBAF are suggested. (LEW)

  13. Sexual excitement.

    PubMed

    Stoller, R J

    1976-08-01

    Sexual excitement depends on a scenario the person to be aroused has been writing since childhood. The story is an adventure, an autobiography disguised as fiction, in which the hero/heroine hides crucial intrapsychic conflicts, mysteries, screen memories of actual traumatic events and the resolution of these elements into a happy ending, best celebrated by orgasm. The function of the fantasy is to take these painful experiences and convert them to pleasure-triumph. In order to sharpen excitement-the vibration between the fear of original traumas repeating and the hope of a pleasurable conclusion this time-one introduces into the story elements of risk (approximations of the trauma) meant to prevent boredom and safety factors (sub-limnal signals to the storyteller that the risk are not truly dangerous). Sexual fantasy can be studied by means of a person's daydreams (including those chosen in magazines, books, plays, television, movies, and outright pornography), masturbatory behavior, object choice, foreplay, techniques of intercourse, or postcoital behavior. PMID:949223

  14. Limited rotational and rovibrational line lists computed with highly accurate quartic force fields and ab initio dipole surfaces.

    PubMed

    Fortenberry, Ryan C; Huang, Xinchuan; Schwenke, David W; Lee, Timothy J

    2014-02-01

    In this work, computational procedures are employed to compute the rotational and rovibrational spectra and line lists for H2O, CO2, and SO2. Building on the established use of quartic force fields, MP2 and CCSD(T) Dipole Moment Surfaces (DMSs) are computed for each system of study in order to produce line intensities as well as the transition energies. The computed results exhibit a clear correlation to reference data available in the HITRAN database. Additionally, even though CCSD(T) DMSs produce more accurate intensities as compared to experiment, the use of MP2 DMSs results in reliable line lists that are still comparable to experiment. The use of the less computationally costly MP2 method is beneficial in the study of larger systems where use of CCSD(T) would be more costly. PMID:23692860

  15. Automatic Generation of Analytic Equations for Vibrational and Rovibrational Constants from Fourth-Order Vibrational Perturbation Theory

    NASA Astrophysics Data System (ADS)

    Matthews, Devin A.; Gong, Justin Z.; Stanton, John F.

    2014-06-01

    The derivation of analytic expressions for vibrational and rovibrational constants, for example the anharmonicity constants χij and the vibration-rotation interaction constants α^B_r, from second-order vibrational perturbation theory (VPT2) can be accomplished with pen and paper and some practice. However, the corresponding quantities from fourth-order perturbation theory (VPT4) are considerably more complex, with the only known derivations by hand extensively using many layers of complicated intermediates and for rotational quantities requiring specialization to orthorhombic cases or the form of Watson's reduced Hamiltonian. We present an automatic computer program for generating these expressions with full generality based on the adaptation of an existing numerical program based on the sum-over-states representation of the energy to a computer algebra context. The measures taken to produce well-simplified and factored expressions in an efficient manner are discussed, as well as the framework for automatically checking the correctness of the generated equations.

  16. Molecular rovibrational dynamics investigated by two-photon wavepacket interferometry with phase-locked pulse pairs

    NASA Astrophysics Data System (ADS)

    Cao, Ying; Zhang, Liang; Yang, Yan; Sun, Zhenrong; Wang, Zugeng

    2007-07-01

    Time-resolved two-photon fluorescence spectra have been investigated based on wavepacket interferometry (WPI), and the wavepacket dynamics of the excited states for 4-dicyanomethylene-2-methyl-6- p-dimethyl-aminostryryl-4H-pyran (DCM) is determined by phase-locked femtosecond pulse pairs. A relative phase between the femtosecond pulse pairs can be maintained as the delay line scanning, and so the two-photon fluorescence signals will be observed to appear periodically recurring features. It indicates the constructive or destructive interference between two-photon wavepackets on the molecular excited states. The experimental results show that the phase-locked WPI has the potential applications in the wavepacket dynamics of the complicated molecular systems.

  17. Electronic and rovibrational quantum chemical analysis of C3P-: the next interstellar anion?

    NASA Astrophysics Data System (ADS)

    Fortenberry, Ryan C.; Lukemire, Joseph A.

    2015-11-01

    C3P- is analogous to the known interstellar anion C3N- with phosphorus replacing nitrogen in a simple step down the periodic table. In this work, it is shown that C3P- is likely to possess a dipole-bound excited state. It has been hypothesized and observationally supported that dipole-bound excited states are an avenue through which anions could be formed in the interstellar medium. Additionally, C3P- has a valence excited state that may lead to further stabilization of this molecule, and C3P- has a larger dipole moment than neutral C3P (˜6 D versus ˜4 D). As such, C3P- is probably a more detectable astromolecule than even its corresponding neutral radical. Highly accurate quantum chemical quartic force fields are also applied to C3P- and its singly 13C substituted isotopologues in order to provide structures, vibrational frequencies, and spectroscopic constants that may aid in its detection.

  18. Observation of rovibrational dephasing of molecules in parahydrogen crystals by frequency domain spectroscopy

    PubMed

    Katsuki; Momose

    2000-04-10

    Rotation-vibration transitions of methane molecules embedded in parahydrogen crystals were investigated through Fourier transform infrared spectroscopy. Each transition shows extremely sharp peaks with a Lorentzian line shape profile, which indicates the spectra are free from inhomogeneous broadening. The steep temperature dependence of the linewidths observed in the range between 3.7 and 8. 5 K is interpreted to be a result of the pure dephasing relaxation mechanism. A remarkable difference in population relaxation widths between stretching and bending vibrational excited states was also found. PMID:11019071

  19. Modelling non-adiabatic effects in H{sub 3}{sup +}: Solution of the rovibrational Schrödinger equation with motion-dependent masses and mass surfaces

    SciTech Connect

    Mátyus, Edit; Szidarovszky, Tamás

    2014-10-21

    Introducing different rotational and vibrational masses in the nuclear-motion Hamiltonian is a simple phenomenological way to model rovibrational non-adiabaticity. It is shown on the example of the molecular ion H{sub 3}{sup +}, for which a global adiabatic potential energy surface accurate to better than 0.1 cm{sup −1} exists [M. Pavanello, L. Adamowicz, A. Alijah, N. F. Zobov, I. I. Mizus, O. L. Polyansky, J. Tennyson, T. Szidarovszky, A. G. Császár, M. Berg et al., Phys. Rev. Lett. 108, 023002 (2012)], that the motion-dependent mass concept yields much more accurate rovibrational energy levels but, unusually, the results are dependent upon the choice of the embedding of the molecule-fixed frame. Correct degeneracies and an improved agreement with experimental data are obtained if an Eckart embedding corresponding to a reference structure of D{sub 3h} point-group symmetry is employed. The vibrational mass of the proton in H{sub 3}{sup +} is optimized by minimizing the root-mean-square (rms) deviation between the computed and recent high-accuracy experimental transitions. The best vibrational mass obtained is larger than the nuclear mass of the proton by approximately one third of an electron mass, m{sub opt,p}{sup (v)}=m{sub nuc,p}+0.31224 m{sub e}. This optimized vibrational mass, along with a nuclear rotational mass, reduces the rms deviation of the experimental and computed rovibrational transitions by an order of magnitude. Finally, it is shown that an extension of the algorithm allowing the use of motion-dependent masses can deal with coordinate-dependent mass surfaces in the rovibrational Hamiltonian, as well.

  20. Rovibrational energy transfer in the He-C3 collision: rigid bender treatment of the bending-rotation interaction and rate coefficients

    NASA Astrophysics Data System (ADS)

    Stoecklin, Thierry; Denis-Alpizar, Otoniel; Halvick, Philippe

    2015-06-01

    C3 is a molecular chain which has been observed in interstellar clouds and in comets. It is also a very floppy molecule for which the vibrational bending transitions are in the same energy range as the rotational transitions. In this paper, we apply our recently developed quantum scattering method for treating atom rigid bender inelastic collisions at the Close Coupling level to the collision of C3 by helium. This method allows us to compute the rovibrational transitions induced by collisions. The purely rotational transitions have been also calculated, using the rigid monomer approximation. The accuracy of this last approximation in the case of a system with a significant vibrational-rotational coupling is discussed. The first evaluation of the cross-sections associated with the rovibrational transitions between levels belonging to different vibrational bending levels is also presented. We observe that the propensity rule for the rovibrational transitions is a competition between the smallest Δj and the smallest transition energy. As a consequence, cross-sections and rate coefficients of vibrationally inelastic transitions can be several orders of magnitude larger than for purely rotational transitions.

  1. High resolution ro-vibrational analysis of interacting bands ν4, ν7, ν10, and ν12 of 13C2H4

    NASA Astrophysics Data System (ADS)

    Ulenikov, O. N.; Gromova, O. V.; Bekhtereva, E. S.; Maul, C.; Bauerecker, S.; Gabona, M. G.; Tan, T. L.

    2015-01-01

    High accurate, ~ 1 ×10-4cm-1, ro-vibrational spectra of the C132H4 molecule in the region of 600-1600 cm-1 were recorded with Bruker IFS 120/125 HR Fourier transform interferometers and analyzed in the Hamiltonian model which takes into account Coriolis resonance interactions between all four bands. More than 660, 3870, 2420, and 2550 transitions belonging to the ν4, ν7, ν10, and ν12 bands were assigned in the experimental spectrum with the maximum values of quantum numbers Jmax. /Kamax ., equal to 38/10, 43/21, 33/16 and 52/18, respectively. To make the ro-vibrational analysis physically more suitable, the initial values of the rotational and centrifugal distortion parameters of the studied bands were theoretically estimated by the use of isotopic relations. On that basis, a set of 55 vibrational, rotational, centrifugal distortion, and resonance interaction parameters was obtained from the fit. They reproduce values of 2934 initial "experimental" ro-vibrational energy levels obtained from nonsaturated unblended lines (more than 9500 assigned transitions of the ν4, ν7, ν10, and ν12 bands) with the rms error drms = 0.00014cm-1. Ground state parameters of the C132H4 molecule were improved as well.

  2. Electronic structure and rovibrational properties of ZnOH in the tilde{X} 2A^' electronic state: A computational molecular spectroscopy study

    NASA Astrophysics Data System (ADS)

    Hirano, Tsuneo; Andaloussi, Mounir Ben Dahman; Nagashima, Umpei; Jensen, Per

    2014-09-01

    The three-dimensional ground-state potential energy surface of ZnOH has been calculated ab initio at the MR-SDCI+Q_DK3/[QZP ANO-RCC (Zn, O, H)] level of theory and used as basis for a study of the rovibrational properties carried out by means of the program MORBID (Morse Oscillator Rigid Bender Internal Dynamics). The electronic ground state is 2A' (correlating with 2Σ+ at the linear configuration). The equilibrium structure has re(Zn-O) = 1.8028 Å, re(O-H) = 0.9606 Å, and ∠e(Zn-O-H) = 114.9°. The Zn-O bond is essentially ionic, with appreciable covalency. The bonding character is compared with those of FeOH (quasi-linear) and CsOH (linear). The rovibrationally averaged structural parameters, determined as expectation values over MORBID wavefunctions, are ⟨r(Zn-O)⟩0 = 1.8078 Å, ⟨r(O-H)⟩0 = 0.9778 Å, and ⟨∠(Zn-O-H)⟩0 = 117°. The Yamada-Winnewisser quasi-linearity parameter is found to be γ0 = 0.84, which is close to 1.0 as expected for a bent molecule. Since no experimental rovibrational spectrum has been reported thus far, this spectrum has been simulated from the ab initio potential energy and dipole moment surfaces. The amphoteric character of ZnOH is also discussed.

  3. Electronic structure and rovibrational properties of ZnOH in the X̃²A' electronic state: a computational molecular spectroscopy study.

    PubMed

    Hirano, Tsuneo; Andaloussi, Mounir Ben Dahman; Nagashima, Umpei; Jensen, Per

    2014-09-01

    The three-dimensional ground-state potential energy surface of ZnOH has been calculated ab initio at the MR-SDCI+Q_DK3/[QZP ANO-RCC (Zn, O, H)] level of theory and used as basis for a study of the rovibrational properties carried out by means of the program MORBID (Morse Oscillator Rigid Bender Internal Dynamics). The electronic ground state is  (2)A' (correlating with (2)Σ(+) at the linear configuration). The equilibrium structure has r(e)(Zn-O) = 1.8028 Å, r(e)(O-H) = 0.9606 Å, and ∠e(Zn-O-H) = 114.9°. The Zn-O bond is essentially ionic, with appreciable covalency. The bonding character is compared with those of FeOH (quasi-linear) and CsOH (linear). The rovibrationally averaged structural parameters, determined as expectation values over MORBID wavefunctions, are ⟨r(Zn-O)⟩0 = 1.8078 Å, ⟨r(O-H)⟩0 = 0.9778 Å, and ⟨∠(Zn-O-H)⟩0 = 117°. The Yamada-Winnewisser quasi-linearity parameter is found to be γ0 = 0.84, which is close to 1.0 as expected for a bent molecule. Since no experimental rovibrational spectrum has been reported thus far, this spectrum has been simulated from the ab initio potential energy and dipole moment surfaces. The amphoteric character of ZnOH is also discussed. PMID:25194373

  4. Ab initio calculation of the ro-vibrational spectrum of H2F+

    NASA Astrophysics Data System (ADS)

    Kyuberis, Aleksandra A.; Lodi, Lorenzo; Zobov, Nikolai F.; Polyansky, Oleg L.

    2015-10-01

    An ab initio study of the rotation-vibrational spectrum of the electronic ground state of the (gas-phase) fluoronium ion H2F+ is presented. A new potential energy surface (PES) and a new dipole moment surface (DMS) were produced and used to compute rotation-vibrational energy levels, line positions and line intensities. Our computations achieve an accuracy of 0.15 cm-1 for the fundamental vibrational frequencies, which is about 50 times more accurate than previous ab initio results. The computed room-temperature line list should facilitate the experimental observations of new H2F+ lines, in particular of yet unobserved overtone transitions. The H2F+ molecular ion, which is isoelectronic to water, has a non-linear equilibrium geometry but a low-energy barrier to linearity at about 6000 cm-1. As a result the effects of so-called quantum monodromy become apparent already at low bending excitations. An analysis of excited bends in terms of quantum monodromy is presented.

  5. Reduced dimension rovibrational variational calculations of the S{sub 1} state of C{sub 2}H{sub 2}. II. The S{sub 1} rovibrational manifold and the effects of isomerization

    SciTech Connect

    Changala, P. Bryan Baraban, Joshua H.; Field, Robert W.; Stanton, John F.; Merer, Anthony J.

    2014-01-14

    Reduced dimension variational calculations have been performed for the rovibrational level structure of the S{sub 1} state of acetylene. The state exhibits an unusually complicated level structure, for various reasons. First, the potential energy surface has two accessible conformers, trans and cis. The cis conformer lies about 2700 cm{sup −1} above the trans, and the barrier to cis-trans isomerization lies about 5000 cm{sup −1} above the trans minimum. The trans vibrations ν{sub 4} (torsion) and ν{sub 6} (asym. bend) interact very strongly by Darling-Dennison and Coriolis resonances, such that their combination levels and overtones form polyads with unexpected structures. Both conformers exhibit very large x{sub 36} cross-anharmonicity since the pathway to isomerization is a combination of ν{sub 6} and ν{sub 3} (sym. bend). Near the isomerization barrier, the vibrational levels show an even-odd K-staggering of their rotational levels as a result of quantum mechanical tunneling through the barrier. The present calculations address all of these complications, and reproduce the observed K-structures of the bending and C–C stretching levels with good qualitative accuracy. It is expected that they will assist with the assignment of the irregular patterns near the isomerization barrier.

  6. Pressure broadening, -shift, speed dependence and line mixing in the ν3 rovibrational band of N2O

    NASA Astrophysics Data System (ADS)

    Loos, Joep; Birk, Manfred; Wagner, Georg

    2015-01-01

    In this paper, we report measured air-broadening, -shift, speed dependence and Rosenkranz line mixing parameters for the ν3 fundamental rovibrational band of N2O. A Bruker IFS 125HR Fourier transform spectrometer was used with a White-type multipass absorption cell with 46.4 m absorption path length to measure four ambient temperature air-broadened absorption spectra at total pressures ranging from 100 to 1000 mbar. A multispectrum fitting technique was used to retrieve parameters up to |m|=40 (m=-J″ and m=J″+1 for the P and R branch, respectively) utilizing the partially correlated quadratic speed-dependent hard collision model including Rosenkranz line mixing. Speed dependence of the broadening parameter as well as line mixing could be observed in the spectra. The broadening parameters are compared to HITRAN2012, where deviations can be ascribed to the influence of neglecting speed dependence effects in spectra analyses when using the Voigt line profile. The line mixing coefficients show a smooth dependence on m.

  7. HIGH-RESOLUTION NEAR-INFRARED SPECTROSCOPY OF HD 100546. II. ANALYSIS OF VARIABLE ROVIBRATIONAL CO EMISSION LINES

    SciTech Connect

    Brittain, Sean D.; Liskowsky, Joseph; Najita, Joan R.; Carr, John S.; Troutman, Matthew R.; Doppmann, Greg W. E-mail: jliskow@clemson.edu E-mail: carr@nrl.navy.mil E-mail: gdoppmann@keck.hawaii.edu

    2013-04-20

    We present observations of rovibrational CO in HD 100546 from four epochs spanning 2003 January through 2010 December. We show that the equivalent widths of the CO lines vary during this time period with the v = 1-0 CO lines brightening more than the UV fluoresced lines from the higher vibrational states. While the spectroastrometric signal of the hot band lines remains constant during this period, the spectroastrometric signal of the v = 1-0 lines varies substantially. At all epochs, the spectroastrometric signals of the UV fluoresced lines are consistent with the signal one would expect from gas in an axisymmetric disk. In 2003, the spectroastrometric signal of the v = 1-0 P26 line was symmetric and consistent with emission from an axisymmetric disk. However, in 2006 there was no spatial offset of the signal detected on the red side of the profile, and in 2010 the spectroastrometric offset was yet more strongly reduced toward zero velocity. A model is presented that can explain the evolution of the equivalent width of the v = 1-0 P26 line and its spectroastrometric signal by adding to the system a compact source of CO emission that orbits the star near the inner edge of the disk. We hypothesize that such emission may arise from a circumplanetary disk orbiting a gas giant planet near the inner edge of the circumstellar disk. We discuss how this idea can be tested observationally and be distinguished from an alternative interpretation of random fluctuations in the disk emission.

  8. Gas Phase Rovibrational Spectroscopy of Dmso, PART.I: when a Synchrotron Source Reveals AN Unusual Rotational Behaviour

    NASA Astrophysics Data System (ADS)

    Cuisset, Arnaud; Sadovskii, Dmitrii A.; Pirali, Olivier

    2013-06-01

    Many of us have enjoyed the spectacle of a spinning top influenced by friction: rotating rapidly about a stable stationary axis, the top loses slowly its angular momentum j (and energy), slows down gradually, and then, suddenly, its axis becomes unstable, the top wobbles, and an abrupt change of the top's position follows. In other words, the system undergoes a bifurcation. In the case of the tippe top, rotation about its lower point is stable at low values of angular momentum J and becomes unstable at large J. Something quite similar occurs in a freely rotating dimethylsulfoxyde (DMSO, (CH_3)_2SO) molecule. For the first time in such large polyatomic molecule a quantum bifurcation induced by a gyroscopic destabilization was observed. This unusual phenomenon in rotational dynamics was discovered in the rovibrational states of the bending fundamental ν_{23} band of DMSO whose high-resolution gas phase absorption spectrum was observed along with that of ν_{11} by Cuisset et al. using the exceptional properties of the AILES beamline in the Far-Infrared domain. A. Cuisset, O. Pirali, D. Sadovskii,Phys. Rev. Lett., 109,(094101), 2012. A. Cuisset, L. Nanobashvili, I. Smirnova, R. Bocquet, F. Hindle, G. Mouret, O. Pirali, P. Roy, D. Sadovskii,Chem. Phys. Lett., 492,(30),2010 J. B. Brubach et al., AIP Conf. Proc., 1214, (81), 2010.

  9. Potential interstellar noble gas molecules: ArOH+ and NeOH+ rovibrational analysis from quantum chemical quartic force fields

    NASA Astrophysics Data System (ADS)

    Theis, Riley A.; Fortenberry, Ryan C.

    2016-03-01

    The discovery of ArH+ in the interstellar medium has shown that noble gas chemistry may be of more chemical significance than previously believed. The present work extends the known chemistry of small noble gas molecules to NeOH+ and ArOH+. Besides their respective neonium and argonium diatomic cation cousins, these hydroxyl cation molecules are the most stable small noble gas molecules analyzed of late. ArOH+ is once again more stable than the neon cation, but both are well-behaved enough for a complete quartic force field analysis of their rovibrational properties. The Ar-O bond in ArOH+ , for instance, is roughly three-quarters of the strength of the Ar-H bond in ArH+ highlighting the rigidity of this system. The rotational constants, geometries, and vibrational frequencies for both molecules and their various isotopologues are computed from ab initio quantum chemical theory at high-level, and it is shown that these cations may form in regions where peroxy or weakly-bound alcohols may be present. The resulting data should be of significant assistance for the laboratory or observational analysis of these potential interstellar molecules.

  10. Rovibrational molecular populations, atoms, and negative ions in H/sub 2/ and D/sub 2/ magnetic multicusp discharges

    SciTech Connect

    Pealat, M.; Taran, J.E.; Bacal, M.; Hillion, F.

    1985-06-01

    Coherent anti-Stokes Raman scattering is applied to the study of rovibrational populations in magnetic multicusp H/sub 2/ and D/sub 2/ discharges. This subject is of interest to negative hydrogen ion formation by volume plasma processes. The populations of high-lying rotational states (J>5) in the vibrational levels v = 0, 1, and 2 are found to be significantly higher than expected from the Boltzmann law. In H/sub 2/ the net populations of the first four vibrational levels follow approximately the Boltzmann law, with the vibrational temperature of 2390 K (in a 90 V-10 A discharge at 55 ..mu..bar). In similar discharge conditions, the population of the state v = 3 in D/sub 2/ is higher than expected from the Boltzmann law. In the presence of the discharge a deficiency in H/sub 2/ and D/sub 2/ molecule density was observed and was attributed to the possible presence of H and D atoms. This was verified by an independent measurement of the atomic fraction and temperature. The density of negative ions, measured by the photodetachment technique, is also reported.