264 research outputs found
Using Wave-Packet Interferometry to Monitor the External Vibrational Control of Electronic Excitation Transfer
We investigate the control of electronic energy transfer in molecular dimers
through the preparation of specific vibrational coherences prior to electronic
excitation, and its observation by nonlinear wave-packet interferometry.
Laser-driven coherent nuclear motion can affect the instantaneous resonance
between site-excited electronic states and thereby influence short-time
electronic excitation transfer (EET). We first illustrate this control
mechanism with calculations on a dimer whose constituent monomers undergo
harmonic vibrations. We then consider the use of nonlinear wave-packet
interferometry (nl-WPI) experiments to monitor the nuclear dynamics
accompanying EET in general dimer complexes following impulsive vibrational
excitation by a sub-resonant control pulse (or control pulse sequence). In
measurements of this kind, two pairs of polarized phase-related femtosecond
pulses following the control pulse generate superpositions of coherent nuclear
wave packets in optically accessible electronic states. Interference
contributions to the time- and frequency-integrated fluorescence signal due to
overlaps among the superposed wave packets provide amplitude-level information
on the nuclear and electronic dynamics. We derive the basic expression for a
control-pulse-dependent nl-WPI signal. The electronic transition moments of the
constituent monomers are assumed to have a fixed relative orientation, while
the overall orientation of the complex is distributed isotropically. We include
the limiting case of coincident arrival by pulses within each phase-related
pair in which control-influenced nl-WPI reduces to a fluorescence-detected
pump-probe difference experiment. Numerical calculations of pump-probe signals
based on these theoretical expressions are presented in the following paper
Quasiparticle interfacial level alignment of highly hybridized frontier levels: HO on TiO(110)
Knowledge of the frontier levels' alignment prior to photo-irradiation is
necessary to achieve a complete quantitative description of HO
photocatalysis on TiO(110). Although HO on rutile TiO(110) has been
thoroughly studied both experimentally and theoretically, a quantitative value
for the energy of the highest HO occupied levels is still lacking. For
experiment, this is due to the HO levels being obscured by hybridization
with TiO(110) levels in the difference spectra obtained via ultraviolet
photoemission spectroscopy (UPS). For theory, this is due to inherent
difficulties in properly describing many-body effects at the
HO-TiO(110) interface. Using the projected density of states (DOS) from
state-of-the-art quasiparticle (QP) , we disentangle the adsorbate and
surface contributions to the complex UPS spectra of HO on TiO(110). We
perform this separation as a function of HO coverage and dissociation on
stoichiometric and reduced surfaces. Due to hybridization with the TiO(110)
surface, the HO 3a and 1b levels are broadened into several peaks
between 5 and 1 eV below the TiO(110) valence band maximum (VBM). These
peaks have both intermolecular and interfacial bonding and antibonding
character. We find the highest occupied levels of HO adsorbed intact and
dissociated on stoichiometric TiO(110) are 1.1 and 0.9 eV below the VBM. We
also find a similar energy of 1.1 eV for the highest occupied levels of HO
when adsorbed dissociatively on a bridging O vacancy of the reduced surface. In
both cases, these energies are significantly higher (by 0.6 to 2.6 eV) than
those estimated from UPS difference spectra, which are inconclusive in this
energy region. Finally, we apply self-consistent QP (scQP1) to obtain
the ionization potential of the HO-TiO(110) interface.Comment: 12 pages, 12 figures, 1 tabl
Formation of the in Two-Photon Collisions at LEP
The two-photon width of the meson has been
measured with the L3 detector at LEP. The is studied in the decay
modes , KK, KK,
KK, , , and
using an integrated luminosity of 140 pb at GeV and
of 52 pb at GeV. The result is
(BR) keV. The dependence of the cross section is studied for
GeV. It is found to be better described by a Vector Meson
Dominance model form factor with a J-pole than with a -pole. In addition,
a signal of events is observed at the mass. Upper limits
for the two-photon widths of the , , and are also
given
CASSCF calculations for photoinduced processes in large molecules: Choosing when to use the RASSCF, ONIOM and MMVB approximations
Search for Heavy Neutral and Charged Leptons in ee Annihilation at = 183 and 189 GeV
A search for unstable neutral and charged heavy leptons as well as for stable
charged heavy leptons is performed at center-of-mass energies = 183
and 189 GeV with the L3 detector at LEP. No evidence for their existence is
found. We exclude neutral heavy leptons which couple to the electron, muon or
tau family, of the Dirac type for masses below 92.4, 93.3 and 83.3 GeV, and of
the Majorana type for masses below 81.8, 84.1 and 73.5 GeV, respectively. We
exclude unstable charged heavy leptons for masses below 93.9 GeV for a wide
range of the associated neutral heavy lepton mass. If the unstable charged
heavy lepton decays to a light neutrino, we exclude masses below 92.4 GeV. The
production of stable charged heavy leptons with mass less than 93.5 GeV is also
excluded
Measurement of Mass and Width of the W Boson at LEP
We report on measurements of the mass and total decay width of the W boson
with the L3 detector at LEP. W-pair events produced in
interactions between 161 GeV and 183 GeV centre-of-mass energy are selected in
a data sample corresponding to a total luminosity of 76.7 pb. Combining
all final states in W-pair production, the mass and total decay width of the W
boson are determined to be GeV and
GeV, respectively
Measurement of an Elongation of the Pion Source in Z Decays
We measure Bose-Einstein correlations between like-sign charged pion pairs in
hadronic Z decays with the L3 detector at LEP. The analysis is performed in
three dimensions in the longitudinal center-of-mass system. The pion source is
found to be elongated along the thrust axis with a ratio of transverse to
longitudinal radius of
A global picture of the S-1/S-0 conical intersection seam of benzene
A global picture of the S1/S0intersection seam of benzene is presented. Eleven new conical intersection critical points were located at the CASSCF level, the connectivity was mapped and the energies refined with CASPT 2. There are two seam branches related with pairs of degenerate A1g/B2uand Egstates at D6hsymmetry, respectively, and the two branches are connected by a seam segment of Cssymmetry. The global energy minimum of the seam is the half-boat shaped intersection that leads to a pre-fulvenic intermediate [I.J. Palmer, I.N. Ragazos, F. Bernardi, M. Olivucci, M.A. Robb, J. Am. Chem. Soc. 115 (1993) 673]. Several other intersections that can lead to the same intermediate or vibrationally hot benzene lie in a range of 3.7 eV above the global seam minimum. There is a recurrent connectivity pattern where permutationally isomeric seam segments are connected by intersections of a higher symmetry point groupThis work has been supported by Grant CTQ2008-06696 from the Spanish Ministerio de Ciencia e Innovación (MICINN
Cerium Oxide Nanoparticles Protect Cardiac Progenitor Cells from Oxidative Stress
Cardiac progenitor cells (CPCs) are a promising autologous source of cells for cardiac
regenerative medicine. However, CPC culture in vitro requires the presence of microenvironmental
conditions (a complex array of bioactive substance concentration, mechanostructural
factors, and physicochemical factors) closely mimicking the natural cell surrounding in vivo,
including the capability to uphold reactive oxygen species (ROS) within physiological levels
in vitro. Cerium oxide nanoparticles (nanoceria) are redox-active and could represent a potent
tool to control the oxidative stress in isolated CPCs. Here, we report that 24 h exposure to 5, 10,
and 50 !g/mL of nanoceria did not a!ect cell growth and function in cardiac progenitor cells,
while being able to protect CPCs from H2O2-induced cytotoxicity for at least 7 days, indicating
that nanoceria in an e!ective antioxidant. Therefore, these "ndings con"rm the great
potential of nanoceria for controlling ROS-induced cell damage
Heavy Quarkonium Production in Z Decays
We report measurements of the inclusive production of heavy quarkonium states in decays based on the analysis of 3.6 million hadronic events collected by the L3 detector at LEP. The measurement of inclusive J production and an improved confidence level upper limit on production are presented. In addition, two independent measurements of the ratio, , of prompt J mesons to those from B decay are made using two different isolation cuts to separate prompt J mesons from J mesons produced in the decays of b hadrons. The results are: % \begin{eqnarray} \mathrm{Br}(\mathrm{Z} \rightarrow \mathrm{J} + \mathrm{X}) & = & (3.21 \pm 0.21 \; \mathrm{(stat.)} \; ^{+ 0.19}_{- 0.28} \; \mathrm{(sys.)} ) \times 10^{-3} \; , \nonumber \\ \mathrm{Br}(\mathrm {Z} \rightarrow \Upsilon(\mathrm{1S} + X) & < & 4.4 \times 10^{-5} \; , \nonumber \\ %% f_{\mathrm{p}} & = & (7.1 \pm 2.1 \; \mathrm{(stat.)} \; \pm 1.2 \; \mathrm{(sys.)} \; ^{+1.5}_{-0.8} \;\mathrm{(theo.)} ) \times 10^{-2} \; . \nonumbe
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