The Experts below are selected from a list of 321 Experts worldwide ranked by ideXlab platform
G Zerbi - One of the best experts on this subject based on the ideXlab platform.
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raman activation in DisorDereD graphites of the a1 symmetry forbiDDen k 0 phonon the origin of the D Line
Journal of Chemical Physics, 2001Co-Authors: Chiara Castiglioni, Fabrizia Negri, M Rigolio, G ZerbiAbstract:The analysis of the tensors of polarizability Derivatives, computeD with quantum-chemical methoDs for several large polycyclic aromatic hyDrocarbon molecules, allows to rationalize the origin of the Raman D Line observeD in DisorDereD graphites as Due to a relaxation of the phonon selection rules. It is shown that a minimal rearrangement of the atomic anD electronic structure in a lattice Different from that of a perfect graphite crystal causes a selective activation of a specific totally symmetric phonon whose frequency falls in the region of the D banD anD whose motion is DominateD by the breathing vibration of aromatic rings. We numerically proof this conjecture on the basis of polarizability Derivatives obtaineD with Density Functional Theory calculations.
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origin of the D Line in the raman spectrum of graphite a stuDy baseD on raman frequencies anD intensities of polycyclic aromatic hyDrocarbon molecules
Journal of Chemical Physics, 2001Co-Authors: Chiara Castiglioni, Fabrizia Negri, C Mapelli, G ZerbiAbstract:A common valence force fielD for polycyclic aromatic hyDrocarbons (PAHs) anD graphite has been useD in orDer to explain their Raman spectra from a unifieD viewpoint. On this basis the correlation observeD between experimental spectra has been explaineD anD rationalizeD. Quantum chemical Density functional theory calculations of Raman intensities of small PAHs have been also performeD, supporting the conclusions obtaineD from the Dynamical analysis. The results obtaineD are useful for the characterization of materials containing graphitic Domains anD proviDe some new insight on the nature of the D peak in DisorDereD graphite.
K M N De Silva - One of the best experts on this subject based on the ideXlab platform.
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kinetic measurements of fluorine bromine anD ioDine atom abstraction reactions at elevateD temperatures by grounD state atomic rubiDium rb 52s1 2 stuDieD by time resolveD laser inDuceD fluorescence
Journal of Photochemistry and Photobiology A-chemistry, 2001Co-Authors: Ernesto Martinez, Jose Albaladejo, Elena Jimenez, Alberto Notario, David Husain, K M N De SilvaAbstract:Abstract The kinetics of a range of halogen atom-abstraction reactions unDergone by atomic rubiDium in its electronic grounD state, Rb(52S1/2), have been investigateD by time-resolveD laser-inDuceD fluorescence at elevateD temperatures. Rb(52S1/2) was generateD in an excess of halogenateD reactant anD He buffer gas by pulseD photolysis of rubiDium haliDe vapours. Two separate experimental systems were employeD operating at the RyDberg transition at λ=420.2 nm {Rb[6p(2P3/2)]→Rb[5s(2S1/2)]} anD at the shorter wavelength component of the spin-orbit resolveD D-Line Doublet transition at λ=780.0 nm {Rb[5s5p(2P3/2)]→Rb[5s(2S1/2)]}. SeconD-orDer rate constants kRX for various F, Br anD I abstraction reactions have been measureD for essentially single-temperature conDitions. These rate constants, which represent a new boDy of absolute rate Data for Rb(2S1/2), are compareD with the values reporteD hitherto by time-resolveD atomic resonance absorption spectroscopy anD with those previously obtaineD for other alkali metal atoms using time-resolveD techniques.
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bromine atom abstraction reactions at elevateD temperatures by grounD state atomic rubiDium investigateD by time resolveD laser inDuceD fluorescence
Journal of Photochemistry and Photobiology A-chemistry, 1997Co-Authors: K M N De Silva, David HusainAbstract:Abstract The collisional behaviour of atomic rubiDium in its 5 s ( 2 S 1 2 ) electronic grounD state with a series of alkyl bromiDes has been investigateD at elevateD temperatures by time-resolveD laser-inDuceD fluorescence (LIF). Rb (5 2 S 1 2 ) was generateD by the pulseD irraDiation of rubiDium haliDe vapours anD monitoreD by time-resolveD laser inDuceD fluorescence (LIF) using the D-Line transition at λ = 780 nm ( Rb (5 2 P 3 2 −5 2 S 1 2 ) exciteD with a pulseD ND-YAG pumpeD Dye-laser coupleD with boxcar integration of the fluorescence signal. LIF Decay profiles for Rb (5 2 S 1 2 ) were recorDeD at Different total pressures with mixtures of an aDDeD alkyl bromiDe (RBr) of fixeD relative composition ƒ = [ RBr ]/ ([ RBr ] + [ He ]) with excess He bath gas, from which absolute rate Data were founD, essentially for single temperatures. The following absolute seconD-orDer rate constants kR (cm3 molecule−1 s−1) are reporteD for the removal of Rb (5 2 S 1 2 ) by the seris of alkyl bromiDes: CH3Br, (2.0±0.1) × 10−11 (875 K); C2H5Br, (1.4±0.1) × 10−11 (875 K); C3H7Br, (1.2±0.1) × 10−11 (876 K); C4H9Br, (1.0±0.1) × 10−11 (875 K); C5H11Br, (1.0±0.1) × 10−11 (876 K); C6H13Br, (1.4±0.1) × 10−11 (876 K). the best of our knowleDge, with the exception of CH3Br anD C2H5Br, no previous stuDies of these reactions with Rb (5 2 S 1 2 ) have been reporteD, anD we believe the present investigation to be the first stuDy of these processes by LIF. These rate constants are compareD, whee possible, with analogous Data for K (4 2 S 1 2 ) , Na (3 2 S 1 2 ) anD Cs (6 2 S 1 2 ) , principally measureD by atomic resonance absorption spectroscopy anD also by LIF.
David Husain - One of the best experts on this subject based on the ideXlab platform.
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kinetic measurements of fluorine bromine anD ioDine atom abstraction reactions at elevateD temperatures by grounD state atomic rubiDium rb 52s1 2 stuDieD by time resolveD laser inDuceD fluorescence
Journal of Photochemistry and Photobiology A-chemistry, 2001Co-Authors: Ernesto Martinez, Jose Albaladejo, Elena Jimenez, Alberto Notario, David Husain, K M N De SilvaAbstract:Abstract The kinetics of a range of halogen atom-abstraction reactions unDergone by atomic rubiDium in its electronic grounD state, Rb(52S1/2), have been investigateD by time-resolveD laser-inDuceD fluorescence at elevateD temperatures. Rb(52S1/2) was generateD in an excess of halogenateD reactant anD He buffer gas by pulseD photolysis of rubiDium haliDe vapours. Two separate experimental systems were employeD operating at the RyDberg transition at λ=420.2 nm {Rb[6p(2P3/2)]→Rb[5s(2S1/2)]} anD at the shorter wavelength component of the spin-orbit resolveD D-Line Doublet transition at λ=780.0 nm {Rb[5s5p(2P3/2)]→Rb[5s(2S1/2)]}. SeconD-orDer rate constants kRX for various F, Br anD I abstraction reactions have been measureD for essentially single-temperature conDitions. These rate constants, which represent a new boDy of absolute rate Data for Rb(2S1/2), are compareD with the values reporteD hitherto by time-resolveD atomic resonance absorption spectroscopy anD with those previously obtaineD for other alkali metal atoms using time-resolveD techniques.
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bromine atom abstraction reactions at elevateD temperatures by grounD state atomic rubiDium investigateD by time resolveD laser inDuceD fluorescence
Journal of Photochemistry and Photobiology A-chemistry, 1997Co-Authors: K M N De Silva, David HusainAbstract:Abstract The collisional behaviour of atomic rubiDium in its 5 s ( 2 S 1 2 ) electronic grounD state with a series of alkyl bromiDes has been investigateD at elevateD temperatures by time-resolveD laser-inDuceD fluorescence (LIF). Rb (5 2 S 1 2 ) was generateD by the pulseD irraDiation of rubiDium haliDe vapours anD monitoreD by time-resolveD laser inDuceD fluorescence (LIF) using the D-Line transition at λ = 780 nm ( Rb (5 2 P 3 2 −5 2 S 1 2 ) exciteD with a pulseD ND-YAG pumpeD Dye-laser coupleD with boxcar integration of the fluorescence signal. LIF Decay profiles for Rb (5 2 S 1 2 ) were recorDeD at Different total pressures with mixtures of an aDDeD alkyl bromiDe (RBr) of fixeD relative composition ƒ = [ RBr ]/ ([ RBr ] + [ He ]) with excess He bath gas, from which absolute rate Data were founD, essentially for single temperatures. The following absolute seconD-orDer rate constants kR (cm3 molecule−1 s−1) are reporteD for the removal of Rb (5 2 S 1 2 ) by the seris of alkyl bromiDes: CH3Br, (2.0±0.1) × 10−11 (875 K); C2H5Br, (1.4±0.1) × 10−11 (875 K); C3H7Br, (1.2±0.1) × 10−11 (876 K); C4H9Br, (1.0±0.1) × 10−11 (875 K); C5H11Br, (1.0±0.1) × 10−11 (876 K); C6H13Br, (1.4±0.1) × 10−11 (876 K). the best of our knowleDge, with the exception of CH3Br anD C2H5Br, no previous stuDies of these reactions with Rb (5 2 S 1 2 ) have been reporteD, anD we believe the present investigation to be the first stuDy of these processes by LIF. These rate constants are compareD, whee possible, with analogous Data for K (4 2 S 1 2 ) , Na (3 2 S 1 2 ) anD Cs (6 2 S 1 2 ) , principally measureD by atomic resonance absorption spectroscopy anD also by LIF.
Chiara Castiglioni - One of the best experts on this subject based on the ideXlab platform.
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raman activation in DisorDereD graphites of the a1 symmetry forbiDDen k 0 phonon the origin of the D Line
Journal of Chemical Physics, 2001Co-Authors: Chiara Castiglioni, Fabrizia Negri, M Rigolio, G ZerbiAbstract:The analysis of the tensors of polarizability Derivatives, computeD with quantum-chemical methoDs for several large polycyclic aromatic hyDrocarbon molecules, allows to rationalize the origin of the Raman D Line observeD in DisorDereD graphites as Due to a relaxation of the phonon selection rules. It is shown that a minimal rearrangement of the atomic anD electronic structure in a lattice Different from that of a perfect graphite crystal causes a selective activation of a specific totally symmetric phonon whose frequency falls in the region of the D banD anD whose motion is DominateD by the breathing vibration of aromatic rings. We numerically proof this conjecture on the basis of polarizability Derivatives obtaineD with Density Functional Theory calculations.
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origin of the D Line in the raman spectrum of graphite a stuDy baseD on raman frequencies anD intensities of polycyclic aromatic hyDrocarbon molecules
Journal of Chemical Physics, 2001Co-Authors: Chiara Castiglioni, Fabrizia Negri, C Mapelli, G ZerbiAbstract:A common valence force fielD for polycyclic aromatic hyDrocarbons (PAHs) anD graphite has been useD in orDer to explain their Raman spectra from a unifieD viewpoint. On this basis the correlation observeD between experimental spectra has been explaineD anD rationalizeD. Quantum chemical Density functional theory calculations of Raman intensities of small PAHs have been also performeD, supporting the conclusions obtaineD from the Dynamical analysis. The results obtaineD are useful for the characterization of materials containing graphitic Domains anD proviDe some new insight on the nature of the D peak in DisorDereD graphite.
Fabrizia Negri - One of the best experts on this subject based on the ideXlab platform.
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raman activation in DisorDereD graphites of the a1 symmetry forbiDDen k 0 phonon the origin of the D Line
Journal of Chemical Physics, 2001Co-Authors: Chiara Castiglioni, Fabrizia Negri, M Rigolio, G ZerbiAbstract:The analysis of the tensors of polarizability Derivatives, computeD with quantum-chemical methoDs for several large polycyclic aromatic hyDrocarbon molecules, allows to rationalize the origin of the Raman D Line observeD in DisorDereD graphites as Due to a relaxation of the phonon selection rules. It is shown that a minimal rearrangement of the atomic anD electronic structure in a lattice Different from that of a perfect graphite crystal causes a selective activation of a specific totally symmetric phonon whose frequency falls in the region of the D banD anD whose motion is DominateD by the breathing vibration of aromatic rings. We numerically proof this conjecture on the basis of polarizability Derivatives obtaineD with Density Functional Theory calculations.
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origin of the D Line in the raman spectrum of graphite a stuDy baseD on raman frequencies anD intensities of polycyclic aromatic hyDrocarbon molecules
Journal of Chemical Physics, 2001Co-Authors: Chiara Castiglioni, Fabrizia Negri, C Mapelli, G ZerbiAbstract:A common valence force fielD for polycyclic aromatic hyDrocarbons (PAHs) anD graphite has been useD in orDer to explain their Raman spectra from a unifieD viewpoint. On this basis the correlation observeD between experimental spectra has been explaineD anD rationalizeD. Quantum chemical Density functional theory calculations of Raman intensities of small PAHs have been also performeD, supporting the conclusions obtaineD from the Dynamical analysis. The results obtaineD are useful for the characterization of materials containing graphitic Domains anD proviDe some new insight on the nature of the D peak in DisorDereD graphite.
