Search results for "Citation"
showing 10 items of 1710 documents
Localized excitation effect on dipole moments of oligophenylenevinylenes in their excited Franck–Condon state
2010
Abstract The results from electrooptical absorption measurements (EOAM) on the ground and excited Franck–Condon state dipole moments of oligophenylenevinylenes in 1,4-dioxane and cyclohexane are presented. The dipole moments of quadrupolar dyes in the ground state are not equal zero. This means that one of the functional end groups of these molecules is not on the axis or on the plane with the central part of the molecule. Such a conclusion is confirmed by the quantum-chemical and semi-empirical recalculations. Owing to disorder in the ground-state geometry of the dyes the π–π conjugated system is located on mostly the plane part of the molecule and in the main this part absorbs the light. …
<title>Level-crossing spectroscopy of the 7, 9, and 10D states of Cs in an external electric field</title>
2007
We discuss experimental and theoretical studies of coherent excitation of magnetic sublevels in n D states of cesium that cross in an external electric field. Crossings of mF magnetic sublevels of hyperfine F levels with ΔmF = ±2 lead to resonances in the linearly polarized laser induced fluorescence, while crossings with ΔmF = ±1 lead to resonances in the circularly polarized laser induced fluorescence. These resonances can be exploited to observe alignment to orientation conversion. From the level crossing signals it is possible to measure atomic properties, such as the tensor polarizability α2 and the hyperfine constant A . Alignment to orientation conversion involves the deformation of …
Energy transfer rates and pathways of single donor chromophores in a multichromophoric dendrimer built around a central acceptor core.
2004
An artificial light-harvesting dendrimer showing highly efficient electronic excitation energy transfer from four peripheral donors to one central acceptor has been investigated by single-molecule spectroscopy at low temperatures. Confocal imaging in combination with frequency selective excitation spectroscopy gives direct access to energy transfer rates of individual donors and allows the determination of energy transfer pathways within a single multichromophoric aggregate.
Consequences of the One-Electron Reduction and Photoexcitation of Unsymmetric Bis-imidazolium Salts
2012
Coupling of uronium salts with in situ generated N-heterocyclic carbenes provides straightforward access to symmetrical [4](2+) and unsymmetrical bis-imidazolium salts [6](2+) and [9](2+) . As indicated by cyclic and square-wave voltammetry, [6](2+) and [9](2+) can be (irreversibly) reduced by one electron. The initially formed radicals [6](.+) and [9](.+) undergo further reactions, which were probed by EPR spectroscopy and density functional calculations. The final products of the two-electron reduction are the two carbenes. Upon irradiation with UV light both [6](2+) and [9](2+) emit at room temperature in solution but with dramatically different characteristics. The different fluorescenc…
Triple-resonance autoionization of uranium optimized for diode laser excitation
2007
Abstract The photoionization of uranium via three-step excitation has been optimized for isotope selective trace analysis. A search found 13 new J = 6, 7, and 8 odd-parity states in the 36,850–37,200 cm− 1 region that allow blue–red–red three-photon excitation at wavelengths favorable for commercial diode laser systems. From each of these 13 states, near-threshold autoionization spectra were recorded at a resolution of 3 × 10− 4 cm− 1. Some 30 even-parity autoionizing levels with J = 5 to 9 have also been observed and characterized. Comparison of the spectra allows J assignment for the new intermediate levels as well as selection of an optimized path for trace analysis. We show that, for a …
On the phase dependence of the interconversion of the motional modes in a Penning trap by quadrupolar excitation
2012
Abstract The interconversion of the radial motional modes in a Penning trap (magnetron and cyclotron modes) by an external quadrupolar rf-field with a frequency near the true cyclotron frequency ω c plays an important role in the measurement cycle of Penning trap mass spectrometry. Ions to be measured are prepared in a state of magnetron motion which is then resonantly converted into cyclotron motion. The data analysis is usually carried out under the assumption that the initial motional state of the ions has been a pure magnetron state. In reality, however, a small component of cyclotron motion is always present in the ion's initial motional state. This component introduces a dependence on…
Long lived photoinduced charges in donor-acceptor anthraquinone substituted thiophene copolymers
2006
The photoinduced charge-transfer properties of a series of polyalkylthiophene copolymers, carrying anthraquinone substituents covalently linked to the conjugated backbone, have been studied in the solid state by photoinduced absorption (PA) and light-induced electron spin resonance (LESR) spectroscopy. The measurements indicate the formation of metastable charges arising from the photoinduced electron transfer from the polythiophene backbone to the anthraquinone moieties. At low temperatures (below 200 K), long-lived persistent charges are formed, exhibiting lifetimes that extend for several minutes; their recombination kinetics has been studied by following the formation and decay of the P…
Dynamics of ground and excited state chlorophylla molecules in pyridine solution probed by femtosecond transient absorption spectroscopy
1999
Abstract Femtosecond pump–probe spectroscopy was used to investigate the ground and excited state dynamics of chlorophyll a (Chl a ) in pyridine following excitation by a 100 fs optical pulse. The transient absorption spectrum and kinetics reveal spectral evolution on two ultrafast time scales: ∼100 fs and ∼3 ps. We attribute these dynamics to ground-state transient hole-burning and solvation dynamics. Transient absorption anisotropy at early times (∼500 fs) was measured for Chl a in pyridine and shows a pronounced wavelength dependence, where anisotropy varies between 0 and 0.5. Strong contribution from excited state absorption is the origin of the variation.
Vibrational analysis of the electronic spectrum of ethylene based onab initio SCF-CI calculations
1972
Ab initio calculations for CH2 twisting and CC stretching vibrational wavefunctions and energy levels are reported for various electronic states of ethylene C2H4. Electronic transition moments between these states are also obtained to allow a calculation of the oscillator strengths for vibrational transitions involved in various electronic band systems; from this study it is concluded that thevertical electronic energy differenceΔE e may differ significantly from the energy of the absorption maximumΔE max with which it is often equated. In particular it is found in the case of theπ→π * singlet-singlet excitation of ethylene that theΔE e value overestimates the most probable vibrational tran…
Ultrafast Electronic and Vibrational Energy Relaxation of Fe(acetylacetonate)3 in Solution
2007
Transient mid-infrared spectroscopy is used to probe the dynamics initiated by excitation of ligand-to-metal (400 nm) and metal-to-ligand (345 nm) charge transfer states of FeIII complexed with acetylacetonate (Fe(acac)3, where acac stands for deprotonated anion of acetylacetone) in solution. Transient spectra in the 1500-1600 cm-1 range show two broad absorptions red-shifted from the bleach of the nu(CO) (approximately 1575 cm-1) and nu(C=C) (approximately 1525 cm-1) ground state absorptions. Bleach recovery kinetics has a time constant of 12-19 ps in chloroform and tetrachloroethylene and it decreases by 30-40% in a 10% mixture of methanol in tetrachloroethylene. The transient absorptions…