The Experts below are selected from a list of 279 Experts worldwide ranked by ideXlab platform
Mehran Mostafavi - One of the best experts on this subject based on the ideXlab platform.
-
ultrafast decay of the Solvated Electron in a neat polar solvent the unusual case of propylene carbonate
Journal of Physical Chemistry Letters, 2016Co-Authors: Sophie Le Caer, Jeanlouis Marignier, Uli Schmidhammer, Daniel Ortiz, Jacqueline Belloni, Mehran MostafaviAbstract:The behavior of carbonates is critical for a detailed understanding of aging phenomena in Li-ion batteries. Here we study the first reaction stages of propylene carbonate (PC), a cyclical carbonate, by picosecond pulse radiolysis. An absorption band with a maximum around 1360 nm is observed at 20 ps after the Electron pulse and is shifted to 1310 nm after 50 ps. This band presents the features of a Solvated Electron absorption band, the solvation lasting up to 50 ps. Surprisingly, in this polar solvent, the Solvated Electron follows an ultrafast decay and disappears with a half time of 360 ps. This is attributed to the formation of a radical anion PC–•. The yield of the Solvated Electron is low, suggesting that the radical anions are mainly directly produced from preSolvated Electrons. These results demonstrate that the initial Electron transfers mechanisms are strongly different in linear compared with cyclical carbonates.
-
direct evidence for transient pair formation between a Solvated Electron and h3o observed by picosecond pulse radiolysis
Journal of Physical Chemistry Letters, 2014Co-Authors: Uli Schmidhammer, Mehran MostafaviAbstract:The reaction between the Solvated Electron and hydronium cation H3O+ in water constitutes a fundamental reaction in chemistry. Due to significant rearrangement of solvent molecules around both the Electron and H3O+, the reaction rate of this process is not controlled by diffusion. The presence of a reaction barrier suggests the formation of an intermediate that has so far not been observed. Here, the time-resolved visible absorption spectra in three concentrated acid solutions, perchloric, sulfuric, and phosphoric, at various concentrations are recorded by the picosecond pulse radiolysis method. In contrast to previous reports, a strong blue shift of the absorption band of the Solvated Electron in acidic solutions compared to neat water is clearly observed, consistent with formation of a pair between the Solvated Electron and hydronium cation.
-
picosecond pulse radiolysis study on the distance dependent reaction of the Solvated Electron with organic molecules in ethylene glycol
Journal of Physical Chemistry A, 2012Co-Authors: Abdel Karim El Omar, Uli Schmidhammer, Pascal Pernot, Shigeo Murata, Mehran MostafaviAbstract:The decay of Solvated Electron es– is observed by nanosecond and picosecond pulsed radiolysis, in diluted and highly concentrated solutions of dichloromethane, CH2Cl2, trichloromethane, CHCl3, tribromomethane, CHBr3, acetone, CH3COCH3, and nitromethane, CH3NO2, prepared in ethylene glycol. First, second-order rate constants for the reactions between e–s and the organic scavengers have been determined. The ratio between the highest rate constant that was found for CH3NO2 and the lowest one that was found for acetone is 3. This difference in reactivity cannot be explained by the change of viscosity or the size of the molecules. Then, from the analysis of decay kinetics obtained using ultrafast pulse–probe method, the distance dependent first-order rate constant of Electron transfer for each scavenger has been determined. The amplitude of the transient effect observed on the picosecond time scale differs strongly between these Solvated Electron scavengers. For an identical scavenger concentration, the transi...
-
pulse radiolysis studies on the temperature dependent spectrum and the time dependent yield of Solvated Electron in propane 1 2 3 triol
Journal of Physical Chemistry A, 2009Co-Authors: Haiying Fu, Vincent De Waele, Isabelle Lampre, Yusa Muroya, Shinichi Yamashita, Yosuke Katsumura, Mehran MostafaviAbstract:With a revisit of the absorption coefficient of the Solvated Electron in propane-1,2,3-triol, the temperature-dependent behavior of the absorption spectrum of Solvated Electron was studied from room temperature to 573 K by pulse radiolysis techniques. The change in the absorption spectrum of Solvated Electron in propane-1,2,3-triol observed by cooling down from a high temperature to 333 K is compared with that occurring during the Electron solvation process at 333 K. The effect of the specific molecular structure of propane-1,2,3-triol compared to other alcohols is discussed.
-
geminate recombination measurements of Solvated Electron in thf using laser synchronized picosecond Electron pulse
Chemical Physics Letters, 2006Co-Authors: Vincent De Waele, Pascal Pernot, Sebastien Sorgues, Jeanlouis Marignier, H Monard, Jeanphilippe Larbre, Mehran MostafaviAbstract:Abstract We report the first study of picosecond pulse radiolysis of neat tetrahydrofuran (THF) by pulse–probe method. It shows a fast decay of absorbance at 790 nm within 2.5 ns. This decay is assigned to Solvated Electron. We observe that, at 30 ps the G value of Solvated Electron in THF is much lower than that of hydrated Electron. Our data on Solvated Electron survival probability are compared with the literature data on the yield measurements with scavenging method.
Paul F Barbara - One of the best experts on this subject based on the ideXlab platform.
-
Detailed Investigations of the Pump−Probe Spectroscopy of the Equilibrated Solvated Electron in Alcohols
Journal of Physical Chemistry A, 1998Co-Authors: Carlos Silva, Peter K. Walhout, Philip J. Reid, Paul F BarbaraAbstract:Pump−probe spectroscopy of the equilibrated Solvated Electron in methanol and ethanol has been studied with ∼300 fs time resolution. At low pump power the observed dynamics are assigned to s → p excitation and subsequent relaxation of a localized Solvated Electron. In contrast, at high pump power, two-photon absorption apparently produces mobile “conduction band” Electrons, which are subsequently trapped and relax at a remote site from the initial equilibrated Electron. The two-photon excitation is also observed to induce an ultrafast proton-transfer reaction from the solvent.
-
detailed investigations of the pump probe spectroscopy of the equilibrated Solvated Electron in alcohols
Journal of Physical Chemistry A, 1998Co-Authors: Carlos Silva, Peter K. Walhout, Philip J. Reid, Paul F BarbaraAbstract:Pump−probe spectroscopy of the equilibrated Solvated Electron in methanol and ethanol has been studied with ∼300 fs time resolution. At low pump power the observed dynamics are assigned to s → p excitation and subsequent relaxation of a localized Solvated Electron. In contrast, at high pump power, two-photon absorption apparently produces mobile “conduction band” Electrons, which are subsequently trapped and relax at a remote site from the initial equilibrated Electron. The two-photon excitation is also observed to induce an ultrafast proton-transfer reaction from the solvent.
-
direct pump probe spectroscopy of the near ir band of the Solvated Electron in alcohols
Chemical Physics Letters, 1995Co-Authors: Peter K. Walhout, Carlos Silva, Philip J. Reid, Joseph C Alfano, Yoshifumi Kimura, Paul F BarbaraAbstract:Abstract We report femtosecond direct pump/probe data on the s-state to p-state transition of the Solvated Electron in alcohols. The data reveal a p-state lifetime of ≈ 0.5 ps and a large spectral component due to displacement along the ground-state solvent coordinate involving slow diffusive solvent motions and subsequent relaxation. The large displacement is surprising considering the short excited-state lifetime and the long relaxation times of these modes. This effect is apparently the result of a previously unknown p-state to s-state nonadiabatic rearrangement of the solvent coordinate of Solvated Electrons in alcohols.
-
femtosecond absorption anisotropy of the aqueous Solvated Electron
Chemical Physics Letters, 1994Co-Authors: Philip J. Reid, Peter K. Walhout, Carlos Silva, Paul F BarbaraAbstract:Abstract Femtosecond near-infrared pump/visible probe absorption dichroism studies on the aqueous Solvated Electron are reported. Experiments performed with 300 fs time resolution demonstrate that the anisotropy of the transient absorption observed at 740, 800 and 860 nm is established concomitant with excitation and decays in ≈ 3 ps. This observation is consistent with recent theoretical predictions (B.J. Schwartz and P.J. Rossky, Phys. Rev. Letters (1994), submitted) and demonstrates that anisotropic solvent fluctuations relax on the picosecond timescale. However, the magnitude and spectral manifestations of the absorption anisotropy are not consistent with theory.
-
ultrafast transient absorption spectroscopy of the Solvated Electron in water
The Journal of Physical Chemistry, 1994Co-Authors: Yoshifumi Kimura, Peter K. Walhout, Joseph C Alfano, Paul F BarbaraAbstract:Ultrafast near-infrared (NIR)-pump/variable wavelength probe transient absorption spectroscopy has been performed on the aqueous Solvated Electron. The photodynamics of the Solvated Electron excited to its p-state are qualitatively similar to previous measurements of the dynamics of photoinjected Electrons at high energy. This result confirms the previous interpretation of photoinjected Electron dynamics as having a rate-limiting bottleneck at low energies presumably involving the p-state. The absorption transients of our NIR-pump experiments obtained probing between 540 and 1060 nm reveal complicated dynamics that cannot be strictly reproduced using a two-state kinetic model, necessitating modification of the two-state model to include ground-state transient solvation and local heating following Electronic relaxation. This modified kinetic model was found to quantitatively reproduce the observed spectral dynamics, yielding an excited-state lifetime of 310 [+-] 80 fs and a 1.1 [+-] 0.2 ps time scale for ground-state cooling and solvation. This model preserves a two-state Electronic relaxation but adds ground-state relaxation dynamics. Excited-state solvation has been neglected in the model, and it remains to be proven whether the observed relaxation processes result from solvation in the ground state, the excited state, or both. 83 refs., 8 figs., 1 tab.
David M Bartels - One of the best experts on this subject based on the ideXlab platform.
-
a simple ab initio model for the Solvated Electron in methanol
Journal of Physical Chemistry A, 2016Co-Authors: Jonathan Walker, David M BartelsAbstract:The solvation structure of a Solvated Electron in methanol is investigated with ab initio calculations of small anion methanol clusters in a polarized dielectric continuum. We find that the lowest-energy structure in best agreement with experiment, calculated with CCSD, MP2, and B3LYP methods with aug-cc-pvdz basis set, is a tetrahedral arrangement of four methanol molecules with OH bonds oriented toward the center. The optimum distance from the tetrahedron center to the hydroxyl protons is ∼1.8 A, significantly smaller than previous estimates. We are able to reproduce experimental radius of gyration Rg (deduced from optical absorption), vertical detachment energy, and resonance Raman frequencies. The Electron paramagnetic resonance g-factor shift is qualitatively reproduced using density functional theory.
-
Solvated Electron spectrum in supercooled water and ice
Chemical Physics Letters, 2007Co-Authors: Yikui Du, Erica A Price, David M BartelsAbstract:Abstract The spectrum of the Solvated Electron was recorded between 310 and 830 nm in water supercooled down to −18 °C, and in ice- I h between −5 °C and −34 °C. The absorption maximum in liquid water continues to blue shift by 0.0022 eV/degree from high temperatures down to −18 °C, regardless of water bulk density. We suggest that the increasing free volume of the water below 4 °C due to formation of tetrahedral bonding structures is unavailable to the Electron. The spectrum of Electrons trapped in a vacancy site in ice- I h is very similar to the liquid on the blue-side, but much narrower on the red side.
-
spur decay kinetics of the Solvated Electron in heavy water radiolysis
Journal of Physical Chemistry A, 2001Co-Authors: David M Bartels, And David Gosztola, Charles D JonahAbstract:Spur decay kinetics of the hydrated Electron following picosecond pulse radiolysis of heavy water have been measured using a time-correlated absorption spectroscopy (TCAS) technique. The TCAS data collected for the first 40 ns of the decay was matched up with single-shot transient digitizer data out to microsecond time scales. The decay shape in heavy water looks exactly like the decay in light water except in the first 10 ns. The “time zero” Solvated Electron yield in heavy water radiolysis must be approximately 7% larger than in light water, to match the best available scavenger product measurements. We propose an explanation in terms of the larger distances traveled by Electrons in heavy water prior to localization. The implication is that preSolvated H2O+ “holes” are very efficient scavengers for the preSolvated conduction band Electrons.
-
spur decay of the Solvated Electron in picosecond radiolysis measured with time correlated absorption spectroscopy
Journal of Physical Chemistry A, 2000Co-Authors: David M Bartels, Andrew R Cook, Mohan Mudaliar, Charles D JonahAbstract:Spur decay kinetics of the hydrated Electron following picosecond pulse radiolysis of water have been measured using a time-correlated transient absorption technique with an asynchronous mode-locked laser. The 11 ns time window afforded by this signal-averaging technique is ideal to match up with more conventional transient absorption measurements taken to microsecond time scales. The precise data recorded in this study require a revision downward of the “time zero” Solvated Electron yield to approximately 4.0 per 100 eV of energy absorbed, to match the best available scavenger product measurements.
Richard A Mathies - One of the best experts on this subject based on the ideXlab platform.
-
structure and dynamics of the Solvated Electron in alcohols from resonance raman spectroscopy
Journal of Physical Chemistry A, 2007Co-Authors: Christina M Stuart, Michael J Tauber, Richard A MathiesAbstract:Resonance Raman (RR) spectroscopy is used to probe the structure and excited-state dynamics of the Solvated Electron in the primary liquid alcohols methanol (MeOH), ethanol (EtOH), n-propanol (n-PrOH), and n-butanol (n-BuOH). The strong resonance enhancements (≥104 relative to pure solvent) of the libration, CO stretch, COH bend, CH3 bend, CH2 bend, and OH stretch reveal significant Franck−Condon coupling of the intermolecular and intramolecular vibrational modes of the solvent to the Electronic excitation of the Solvated Electron. All enhanced bands are fully accounted for by a model of the Solvated Electron that is comprised of several nearby solvent molecules that are only perturbed by the presence of the Electron; no new molecular species are required to explain our data. The 340 cm-1 downshift observed for the OH stretch frequency of e-(MeOH), relative to pure solvent, strongly suggests that the methanol molecules in the first solvent shell have the hydroxyl group directed linearly toward the excess ...
-
resonance raman spectra and vibronic analysis of the aqueous Solvated Electron
Chemical Physics Letters, 2002Co-Authors: Michael J Tauber, Richard A MathiesAbstract:Abstract Resonance Raman spectra of the aqueous Solvated Electron reveal enhancements of the water inter- and intramolecular vibrations demonstrating that Electronic excitation is significantly coupled to these modes. The Raman cross-sections and absorption spectra are quantitatively modeled, yielding an optimized Gaussian homogeneous broadening of 4660 cm −1 (FWHM), inhomogeneous broadening of 2700 cm −1 , and Franck–Condon displacements (Δ) of ∼1 for each of the three librations, 0.4 for the water bend, and 0.2 for the stretch. Frequency downshifts of the resonantly enhanced H2O bend to 1615 cm −1 , and of the stretch to 3100 cm −1 are best explained by charge donation into solvent frontier orbitals.
-
fluorescence and resonance raman spectra of the aqueous Solvated Electron
Journal of Physical Chemistry A, 2001Co-Authors: Richard A MathiesAbstract:Fluorescence and resonance Raman spectroscopy are used to probe the solvent structure and dynamics of the aqueous Solvated Electron. Electrons are generated by 218 nm photolysis of iodide or ferrocyanide, and spectra are obtained with 532 or 683 nm probe wavelengths. Strong resonance enhancement of the water Raman librational bands and intramolecular bend and stretch are observed, and the frequencies of the enhanced intramolecular modes are significantly downshifted from the corresponding bands in pure water. The resonance Raman enhancements show that the s→p transition of the aqueous Solvated Electron is coupled to both inter- and intramolecular solvent modes. A broad fluorescence emission underlying the Raman features and extending past 1600 nm into the near-IR is observed due to the Solvated Electron. The fluorescence quantum yield in H2O is ∼7 × 10-7 and it increases 1.4-fold in D2O. A Strickler−Berg analysis of the absorption and emission spectral profiles indicates a near-IR radiative lifetime of ∼4...
Peter K. Walhout - One of the best experts on this subject based on the ideXlab platform.
-
Detailed Investigations of the Pump−Probe Spectroscopy of the Equilibrated Solvated Electron in Alcohols
Journal of Physical Chemistry A, 1998Co-Authors: Carlos Silva, Peter K. Walhout, Philip J. Reid, Paul F BarbaraAbstract:Pump−probe spectroscopy of the equilibrated Solvated Electron in methanol and ethanol has been studied with ∼300 fs time resolution. At low pump power the observed dynamics are assigned to s → p excitation and subsequent relaxation of a localized Solvated Electron. In contrast, at high pump power, two-photon absorption apparently produces mobile “conduction band” Electrons, which are subsequently trapped and relax at a remote site from the initial equilibrated Electron. The two-photon excitation is also observed to induce an ultrafast proton-transfer reaction from the solvent.
-
detailed investigations of the pump probe spectroscopy of the equilibrated Solvated Electron in alcohols
Journal of Physical Chemistry A, 1998Co-Authors: Carlos Silva, Peter K. Walhout, Philip J. Reid, Paul F BarbaraAbstract:Pump−probe spectroscopy of the equilibrated Solvated Electron in methanol and ethanol has been studied with ∼300 fs time resolution. At low pump power the observed dynamics are assigned to s → p excitation and subsequent relaxation of a localized Solvated Electron. In contrast, at high pump power, two-photon absorption apparently produces mobile “conduction band” Electrons, which are subsequently trapped and relax at a remote site from the initial equilibrated Electron. The two-photon excitation is also observed to induce an ultrafast proton-transfer reaction from the solvent.
-
direct pump probe spectroscopy of the near ir band of the Solvated Electron in alcohols
Chemical Physics Letters, 1995Co-Authors: Peter K. Walhout, Carlos Silva, Philip J. Reid, Joseph C Alfano, Yoshifumi Kimura, Paul F BarbaraAbstract:Abstract We report femtosecond direct pump/probe data on the s-state to p-state transition of the Solvated Electron in alcohols. The data reveal a p-state lifetime of ≈ 0.5 ps and a large spectral component due to displacement along the ground-state solvent coordinate involving slow diffusive solvent motions and subsequent relaxation. The large displacement is surprising considering the short excited-state lifetime and the long relaxation times of these modes. This effect is apparently the result of a previously unknown p-state to s-state nonadiabatic rearrangement of the solvent coordinate of Solvated Electrons in alcohols.
-
femtosecond absorption anisotropy of the aqueous Solvated Electron
Chemical Physics Letters, 1994Co-Authors: Philip J. Reid, Peter K. Walhout, Carlos Silva, Paul F BarbaraAbstract:Abstract Femtosecond near-infrared pump/visible probe absorption dichroism studies on the aqueous Solvated Electron are reported. Experiments performed with 300 fs time resolution demonstrate that the anisotropy of the transient absorption observed at 740, 800 and 860 nm is established concomitant with excitation and decays in ≈ 3 ps. This observation is consistent with recent theoretical predictions (B.J. Schwartz and P.J. Rossky, Phys. Rev. Letters (1994), submitted) and demonstrates that anisotropic solvent fluctuations relax on the picosecond timescale. However, the magnitude and spectral manifestations of the absorption anisotropy are not consistent with theory.
-
ultrafast transient absorption spectroscopy of the Solvated Electron in water
The Journal of Physical Chemistry, 1994Co-Authors: Yoshifumi Kimura, Peter K. Walhout, Joseph C Alfano, Paul F BarbaraAbstract:Ultrafast near-infrared (NIR)-pump/variable wavelength probe transient absorption spectroscopy has been performed on the aqueous Solvated Electron. The photodynamics of the Solvated Electron excited to its p-state are qualitatively similar to previous measurements of the dynamics of photoinjected Electrons at high energy. This result confirms the previous interpretation of photoinjected Electron dynamics as having a rate-limiting bottleneck at low energies presumably involving the p-state. The absorption transients of our NIR-pump experiments obtained probing between 540 and 1060 nm reveal complicated dynamics that cannot be strictly reproduced using a two-state kinetic model, necessitating modification of the two-state model to include ground-state transient solvation and local heating following Electronic relaxation. This modified kinetic model was found to quantitatively reproduce the observed spectral dynamics, yielding an excited-state lifetime of 310 [+-] 80 fs and a 1.1 [+-] 0.2 ps time scale for ground-state cooling and solvation. This model preserves a two-state Electronic relaxation but adds ground-state relaxation dynamics. Excited-state solvation has been neglected in the model, and it remains to be proven whether the observed relaxation processes result from solvation in the ground state, the excited state, or both. 83 refs., 8 figs., 1 tab.
