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111.
M.?Boyle T.?Laarmann K.?Hoffmann M.?Hedén E. E.B.?Campbell C. P.?SchulzEmail author I. V.?Hertel 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2005,36(3):339-351
The electron and nuclear dynamics of C60 fullerenes
irradiated with femtosecond laser pulses are investigated with
photoelectron and photoion spectroscopy. The focus of this work is
the detailed exploration of the population mechanism of Rydberg
levels within the excitation process of neutral C60. The effect
of excitation wavelength, intensity, chirp, and polarization on the
kinetic energy distribution of photoelectrons in single-pulse
experiments gives first insight into the underlying processes. In
combination with time-resolved two-color pump-probe spectroscopy
depending on either pump, or probe pulse intensity, a more complete
picture of the interaction can be drawn. The results point towards a
very interesting but nevertheless complex behavior including four
steps: (i) non-adiabatic multielectron excitation of the HOMO
(hu) → LUMO+1 (t1g) transition; (ii)
thermalization within the hot electron cloud on a time scale below
100 fs, followed by a coupling of energy to vibrational modes of
the molecule via doorway state(s); (iii) population of
electronically excited Rydberg states by multiphoton absorption, and
(iv) single photon ionization from the excited Rydberg states. This
excitation process results in a characteristic sequence of
photoelectron lines in the photoemission spectra. The comparison of
the experimental results with recent theoretical work gives
convincing evidence that non-adiabatic multielectron dynamics (NMED)
plays a key role for the understanding of the response of C60
to short-pulse laser radiation. 相似文献
112.
The dissociation of ethane on Pt{110}-(1 x 2) has been studied using supersonic molecular beam and temperature-programmed reaction techniques. The study unequivocally shows that the stable dissociation product of ethane on Pt{110}-(1 x 2) at all coverages is CCH2 at 350-400 K and CCH at 440 K. Temperature-programmed-reaction (TPR) experiments indicate that the CCH2 species decomposes to CCH with a reaction-limited peak temperature of 430 K. Above 450 K, the CCH species becomes unstable and decomposes with a peak temperature of 540 K. By 600 K, ethane dehydrogenates completely to form a surface carbon layer. The sticking probability is initially 0.02 at 370 K and 0.03 at 600 K and follows a linear (1-2theta) dependence for coverages of up to theta = 0.4 ML, where theta is defined as the number of C2Hx units per (1 x 2) unit cell. However, a much weaker coverage dependence at 800 K suggests that the carbon agglomerates into high-density islands. 相似文献
113.
We study gelation in suspensions of model colloidal particles with short-ranged attractive and long-ranged repulsive interactions by means of three-dimensional fluorescence confocal microscopy. At low packing fractions, particles form stable equilibrium clusters. Upon increasing the packing fraction the clusters grow in size and become increasingly anisotropic until finally associating into a fully connected network at gelation. We find a surprising order in the gel structure. Analysis of spatial and orientational correlations reveals that the gel is composed of dense chains of particles constructed from face-sharing tetrahedral clusters. Our findings imply that dynamical arrest occurs via cluster growth and association. 相似文献
114.
Acosta D Affolder T Albrow MG Ambrose D Amidei D Anikeev K Antos J Apollinari G Arisawa T Artikov A Ashmanskas W Azfar F Azzi-Bacchetta P Bacchetta N Bachacou H Badgett W Barbaro-Galtieri A Barnes VE Barnett BA Baroiant S Barone M Bauer G Bedeschi F Behari S Belforte S Bell WH Bellettini G Bellinger J Benjamin D Beretvas A Bhatti A Binkley M Bisello D Bishai M Blair RE Blocker C Bloom K Blumenfeld B Bocci A Bodek A Bolla G Bolshov A Bortoletto D Boudreau J Bromberg C Brubaker E Budagov J 《Physical review letters》2005,94(17):171802
We report the first largely model independent measurement of charged particle multiplicities in quark and gluon jets, Nq and Ng, produced at the Fermilab Tevatron in pp collisions with a center-of-mass energy of 1.8 TeV and recorded by the Collider Detector at Fermilab. The measurements are made for jets with average energies of 41 and 53 GeV by counting charged particle tracks in cones with opening angles of theta(c) = 0.28, 0.36, and 0.47 rad around the jet axis. The corresponding jet hardness Q = Ejet theta c varies in the range from 12 to 25 GeV. At Q = 19.2 GeV, the ratio of multiplicities r = Ng/Nq is found to be 1.64+/-0.17, where statistical and systematic uncertainties are added in quadrature. The results are in agreement with resummed perturbative QCD calculations. 相似文献
115.
Wiedeking M Tabor SL Pavan J Volya A Aguilar AL Calderin IJ Campbell DB Cluff WT Diffenderfer E Fridmann J Hoffman CR Kemper KW Lee S Riley MA Roeder BT Teal C Tripathi V Wiedenhöver I 《Physical review letters》2005,94(13):132501
Excited states in 20O were populated in the reaction 10Be(14C,alpha) at Florida State University (FSU). Charged particles were detected with a particle telescope consisting of 4 annularly segmented Si surface barrier detectors and gamma radiation was detected with the FSU gamma detector array. Five new states were observed below 6 MeV from the alpha-gamma and alpha-gamma-gamma coincidence data. Shell model calculations suggest that most of the newly observed states are core-excited 1p-1h excitations across the N=Z=8 shell gap. Comparisons between experimental data and calculations for the neutron-rich O and F isotopes imply a steady reduction of the p-sd shell gap as neutrons are added. 相似文献
116.
Dewald EL Suter LJ Landen OL Holder JP Schein J Lee FD Campbell KM Weber FA Pellinen DG Schneider MB Celeste JR McDonald JW Foster JM Niemann C Mackinnon AJ Glenzer SH Young BK Haynam CA Shaw MJ Turner RE Froula D Kauffman RL Thomas BR Atherton LJ Bonanno RE Dixit SN Eder DC Holtmeier G Kalantar DH Koniges AE Macgowan BJ Manes KR Munro DH Murray JR Parham TG Piston K Van Wonterghem BM Wallace RJ Wegner PJ Whitman PK Hammel BA Moses EI 《Physical review letters》2005,95(21):215004
The first hohlraum experiments on the National Ignition Facility (NIF) using the initial four laser beams tested radiation temperature limits imposed by plasma filling. For a variety of hohlraum sizes and pulse lengths, the measured x-ray flux shows signatures of filling that coincide with hard x-ray emission from plasma streaming out of the hohlraum. These observations agree with hydrodynamic simulations and with an analytical model that includes hydrodynamic and coronal radiative losses. The modeling predicts radiation temperature limits with full NIF (1.8 MJ), greater, and of longer duration than required for ignition hohlraums. 相似文献
117.
Gade A Bazin D Brown BA Campbell CM Church JA Dinca DC Enders J Glasmacher T Hansen PG Hu Z Kemper KW Mueller WF Olliver H Perry BC Riley LA Roeder BT Sherrill BM Terry JR Tostevin JA Yurkewicz KL 《Physical review letters》2004,93(4):042501
The 9Be(32Ar, 31Ar)X reaction, leading to the 5/2+ ground state of a nucleus at the proton drip line, has a cross section of 10.4(13) mb at a beam energy of 65.1 MeV/nucleon. This translates into a spectroscopic factor that is only 24(3)% of that predicted by the many-body shell-model theory. We introduce refinements to the eikonal reaction theory used to extract the spectroscopic factor to clarify that this very strong reduction represents an effect of nuclear structure. We suggest that it reflects correlation effects linked to the high neutron separation energy (22.0 MeV) for this state. 相似文献
118.
Busacca CA Grossbach D Campbell SJ Dong Y Eriksson MC Harris RE Jones PJ Kim JY Lorenz JC McKellop KB O'Brien EM Qiu F Simpson RD Smith L So RC Spinelli EM Vitous J Zavattaro C 《The Journal of organic chemistry》2004,69(16):5187-5195
The Boehringer-Ingelheim phosphinoimidazoline (BIPI) ligands were applied to the formation of chiral quaternary centers in the asymmetric Heck reaction. Several different substrates were examined in detail, using more than 70 members of this new ligand class. Hammett relationships were determined through systematic variation of the ligand electronics. All substrates showed essentially the same Hammett behavior, where enantioselectivity increased as the ligands were made more electron-deficient. Ligand optimization has led to catalysts which give the highest enantioselectivities reported to date for these difficult systems. 相似文献
119.
Buffer-gas cooling of NH via the beam loaded buffer-gas method 总被引:1,自引:0,他引:1
D.?Egorov W.?C.?Campbell B.?Friedrich S.?E.?Maxwell E.?Tsikata L.?D.?van?Buuren J.?M.?DoyleEmail author 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2004,31(2):307-311
NH radicals from a molecular beam are cooled using a novel beam-loaded buffer gas method. The radicals are produced in a glow discharge beam source and injected into cryogenic helium gas. Up to 1012 molecules in their ground electronic, vibrational, and rotational state are detected in the buffer gas and translational temperatures under 6 K are achieved. The cooling method presented is general and can be applied to any molecules in a molecular beam.Received: 20 July 2004, Published online: 26 October 2004PACS:
33.80.Ps Optical cooling of molecules; trapping - 34.50.Ez Rotational and vibrational energy transfer - 39.10. + j Atomic and molecular beam sources and techniquesB. Friedrich: Present address: Department of Molecular Physics, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Berlin, Germany. 相似文献
120.
We discuss several examples of synchronous dynamical phenomena in
coupled cell networks
that are unexpected from symmetry considerations, but are natural
using a theory developed by Stewart, Golubitsky, and Pivato. In particular
we demonstrate patterns of synchrony in networks with small numbers of cells
and in lattices (and periodic arrays) of cells that cannot readily be
explained by conventional symmetry considerations. We also show that
different types of dynamics can coexist robustly in single solutions of
systems of coupled identical cells. The examples include a
three-cell system exhibiting equilibria, periodic, and quasiperiodic states
in different cells; periodic $2n\times 2n$ arrays of cells that generate
$2^n$ different patterns of synchrony from one symmetry-generated solution;
and systems exhibiting multirhythms (periodic solutions with rationally
related periods in different cells). Our theoretical results include the
observation that reduced equations on a center manifold of a skew product
system inherit a skew product form. 相似文献