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  • 1
    Electronic Resource
    Electronic Resource
    Photodissociation spectroscopy and dynamics of negative ion clusters. II. CO3−⋅(H2O)1,2,3 (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 82 (1985), S. 2884-2895 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Energy resolved photodissociation studies of CO3−⋅(H2O)n, n=1,2,3 are reported for photon energies ranging from 1.95 to 2.2 eV. The only dissociation channel observed is the loss of all attached water molecules to give unclustered CO3− as the sole photofragment ion. The cross section for this mechanism is substantially higher than that for the bare ion, and the sharp structure observed in the spectrum of the bare ion is nearly lost in the clusters. Analysis of the kinetic energy distributions for the photofragment ions places an upper limit of 20 μs on the lifetime of the excited clusters, and demonstrates that approximately 95% of the excess energy in the cluster remains in the CO3− containing fragment rather than being partitioned into relative translation of the photofragments or into internal motion of the water fragments. The dissociation mechanism begins with a bound–bound 2A1←2B1 transition within the core CO3− ion. Internal conversion returns the core ion to the electronic ground state with substantial vibrational excitation; redistribution of this vibrational energy results in vibrational predissociation of the cluster. The relations of this mechanism to those that occur in the bare ion and to other vibrational predissociation experiments on clusters are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.448236
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  • 2
    Electronic Resource
    Electronic Resource
    Photodissociation dynamics of CO3− (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 82 (1985), S. 134-150 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The dynamics of CO3− photodissociation is studied with a new photodissociation spectrometer that allows kinetic energy-resolved detection of parent ions and photofragments. Kinetic energy release distributions, photodissociation spectra, and the dependence of the photofragment intensity on the laser power and background pressure are presented. Photodissociation of CO3− in the energy range 1.95–2.2 eV leads to CO2+O− fragments, and is found to occur by two distinct mechanisms. These mechanisms involve three electronic states that correlate with CO2+O−—the 2B1 ground state, a 2A1 weakly bound state, and a repulsive 2B2 state. The first mechanism begins with a low cross section 2A1 ← 2B1 transition that gives structure to the spectra. From this intermediate state, a second photon carries the ion to the 2B2 state. Dissociation to the observed photofragments occurs rapidly on the repulsive surface. In this two photon mechanism, at least 20% of the available energy is disposed of in relative translation of photofragments. The second mechanism is also initiated by the 2A1 ← 2B1 transition. Deexcitation of the 2A1 bound state by internal conversion, however, leads to high lying vibrational levels of the ground 2B1 state. These vibrational levels are found to have an enhanced collision-induced dissociation cross section.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.448786
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  • 3
    Electronic Resource
    Electronic Resource
    Central electron temperature enhancements due to sawtooth stabilization during counter electron cyclotron current drive in Tokamak à Configuration Variable (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 2909-2914 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In the Tokamak à Configuration Variable (TCV), the central electron temperature obtained in discharges with counter (CNTR) electron cyclotron current drive (ECCD) is larger than with CO-ECCD or electron cyclotron resonance heating (ECRH) alone. Comparison of experimental results with calculations by the transport code PRETOR [IAEA Technical Conference on Advances in Simulation and Models of Thermonuclear Plasmas. Montreal 142 (International Atomic Energy Agency, Vienna 1992)] indicates that sawtooth stabilization is responsible for the increased confinement time and the attendant twofold enhancement of the central temperature. Sawtooth stabilization is caused in turn by the central safety factor q0 rising above 1 for CNTR-ECCD; by contrast, the simulation results show that q0〈1 in the sawtoothing CO-ECCD and ECRH cases. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.874141
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  • 4
    Electronic Resource
    Electronic Resource
    Steady-state fully noninductive operation with electron cyclotron current drive and current profile control in the tokamak à configuration variable (TCV) : The 42nd annual meeting of the division of plasma physics of the American Physical Society and the 10th international congress on plasma physics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 2199-2207 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Fully noninductive, steady-state electron cyclotron current drive (ECCD) has been demonstrated for the first time in experiments carried out in the tokamak à configuration variable (TCV) [O. Sauter et al., Phys. Rev. Lett. 84, 3322 (2000)]. By appropriately distributing six 0.45 MW ECCD sources over the discharge cross section, fully noninductive, stable, and stationary plasmas with Ip up to 210 kA were obtained for the full discharge duration of 1.9 s, corresponding to more than 900 energy confinement times and more than 10 current redistribution times at an average current drive efficiency η20CD=0.01[1020 A W−1 m−2]. These experiments have also demonstrated for the first time the steady recharging of the ohmic transformer using ECCD only. The effect of localized off-axis electron cyclotron heating (ECH) and EC current drive (ECCD) (co- and counter-) is investigated showing that locally driven currents amounting to only 1% of Ip significantly alter sawtooth periods and crash amplitudes. An improved quasi-stationary core confinement regime, with little or no sawtooth activity, has been obtained by a combination of off-axis ECH and on-axis CNTR–ECCD. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1355317
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  • 5
    Electronic Resource
    Electronic Resource
    Spectroscopic investigation of oxide states responsible for hot-carrier degradation (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 54 (1989), S. 168-169 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Hole-trap states in the gate oxide of a Si metal-oxide-semiconductor field-effect transistor (MOSFET) are investigated by inhomogeneous excimer laser irradiation. Subbandgap ultraviolet light photons with an energy exceeding a threshold lying between 5.5 and 6.4 eV were found to excite electrons from these originally neutral states into the SiO2 conduction band. A fixed positive charge is left behind. The degradation in MOSFET performance due to the irradiation is comparable to that accompanying hot-hole injection. Also, subsequent hot-electron stress changes the device characteristics in a way similar to hot-electron stress following hot-hole stress. It is concluded that the traps responsible for hot-carrier degradation cause the optically induced charge trapping.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.101218
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  • 6
    Electronic Resource
    Electronic Resource
    A comprehensive experimental study of the dynamical interaction of He atoms with Cu(001) surface phonons (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 10155-10172 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present new measurements of inelastic He atom scattering from the surface phonons of Cu(001) as a function of crystal temperature, incident energy, and parallel momentum transfer. A careful subtraction of the multiphonon intensity and other background contributions from the time-of-flight intensities reveals three distinct surface-localized vibrational modes which are ascribed to the Rayleigh phonon, the longitudinal bulk resonance, and a further acoustic bulk resonance at higher energy transfers. The longitudinal resonance couples very strongly to the scattering He atoms and, for a wide range of incident conditions, gives peaks which are more intense than those due to the Rayleigh mode. The energy and momentum dependence of these peak intensities are analyzed with the aid of a simple distorted wave Born approximation, and the different coupling parameters for the two modes are determined and compared with other available data. The incoherent diffuse elastic peak is shown to decrease as a function of parallel momentum transfer according to the theory of Fraunhofer scattering from a random array of point defects. The multiphonon background is shown to be in agreement with a quick scattering approximation. © 1994 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468005
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  • 7
    Electronic Resource
    Electronic Resource
    The transition from single phonon to multiphonon energy transfer in atom–surface collisions (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 1234-1247 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The angular distributions and time-of-flight spectra of nearly monoenergetic He atoms with incident energies of 82 meV and 112 meV have been measured after scattering from a clean Cu(001) surface over a large range of crystal temperatures from 100 K to 1000 K. With increasing temperatures the sharp diffraction and phonon peaks of the low temperature quantum regime become broad and featureless as expected for the multiphonon classical regime. The results are compared with a quantum mechanical theory which is able to explain the height, position, width, and area under the multiphonon maximum. In the classical regime, the temperature dependence of the inelastic intensity indicates that the He atoms are reflected by a smooth vibrating barrier presumably due to the surface electron density, and not by a lattice of discrete repulsive surface atomic cores. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.473220
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  • 8
    Electronic Resource
    Electronic Resource
    A helium atom scattering study of the growth and dynamics of CH4 and C2H6 on Cu(001) (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 2502-2512 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The growth, structure and dynamics of methane and ethane monolayers on Cu(001) have been studied using high resolution helium atom scattering. Specular intensity measurements of the growth behavior reveal an island growth mode for methane and ethane, indicative of an attractive interatomic interaction. Diffraction measurements show that the methane monolayer forms a hexagonal structure, incommensurate in one direction, with a lattice constant of 4.18 Å, while ethane forms a structure with an interatomic distance of 5.10 Å. The frustrated translational vibrations perpendicular to the surface (S mode) of methane and ethane have been measured with inelastic helium scattering and have frequencies of 6.5 meV and 6.8 meV, respectively. In addition, the desorption energies were determined to be 165 meV for methane and 260 meV for ethane, in both cases independent of coverage. These results are compared with recent measurements made for C2H4 and larger alkanes adsorbed on Cu(001). © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.473156
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  • 9
    Electronic Resource
    Electronic Resource
    Helium atom scattering from isolated CO molecules on copper(001) (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 2093-2098 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Angular distributions have been measured for helium atoms scattering from isolated CO molecules chemisorbed on a Cu(001) surface as a function of incident beam energy between 9.4 and 100 meV and surface coverage from 1.3% ML to 9.3% ML. Up to five oscillations are clearly observed in the angular distributions. The parallel wave vector transfers of the peaks vary only slightly with incident energy and are independent of coverage up to 20% of a c(2×2) layer. New hard wall scattering calculations show that all of the distinct peaks observed can be explained by interference structures involving both Fraunhofer diffraction and illuminated face scattering from CO molecules with an approximate hard wall radius of 2.4 A(ring) with no evidence of the classical rainbows predicted in several recent theoretical studies. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472075
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  • 10
    Electronic Resource
    Electronic Resource
    Response to "Comment on ‘Experimental determination of a longitudinal phonon dispersion curve in a quasi-two-dimensional system' " [J. Chem. Phys. 107, 4443 (1997)] (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 4445-4445 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.474806
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