ChemInform Abstract: STABILITAETSGRENZE SOLVATISIERTER ELEKTRONEN IN SUPERKRITISCHEM AMMONIAK IM BEREICH GERINGER DICHTE

Olinger, R.; Hahne, S.; Schindewolf, U.

doi:10.1002/chin.197227057

Cited by 4 publications

(4 citation statements)

References 1 publication

Supporting

Mentioning

Contrasting

Order By: Relevance

“…51 have not been directly observed in the gas phase, and pulse radiolysis studies of ammonia at temperatures well above the liquid-vapor coexistence curve (CEC) have revealed density thresholds below which electron trapping is not observed. 53 The trapped electron yields from these experiments have been analyzed in terms of semi-empirical calculations which lead to reasonable density thresholds at temperatures above the CEC, and which suggest that clusters of 10-12 NH3 molecules may be necessary for trapping, at least at the temperatures corresponding to the experimental work.54 Water vapor at densities as low as ~5 X 10~3 g/cc still appears to trap electrons at temperatures near the CEC,55 but there is the possibility that a threshold may appear at higher temperatures where density fluctuations are less important.…”

Section: Resultsmentioning

confidence: 99%

Role of ab initio calculations in elucidating properties of hydrated and ammoniated electrons

Newton¹

1975

J. Phys. Chem.

186

View full text Add to dashboard Cite

The properties of solvated electrons are analyzed in terms of a self-consistent modified continuum model based on the techniques of ab initio molecular quantum mechanics. The model is semiclassical in spirit, employing the quantum mechanical density for the excess charge and the first solvation shell in conjunction with classical electrostatics, and is developed in a general form which can be straightforwardly applied to special cases of interest, such as the solvated mono-and dielectron complexes. The advantages and disadvantages of the technique are discussed in relation to other, more empirical approaches. Computational results are presented for excess electrons (mono-and dielectrons) in water and ammonia, and the role of long-range polarization of the medium in localizing the excess charge is analyzed. The variationally determined ground states are characterized in terms of equilibrium solvation shell geometry (appreciable cavities are implied for both water and ammonia), solvation energy, photoionization energy, and charge distribution. The finding of negative spin densities at the first solvent shell protons underscores the importance of a many electron theoretical treatment. Preliminary results for excited states are also reported. The calculated results are compared with experimental and other theoretical data, and the sensitivity of the results to various features of the model are discussed. Particular attention is paid to the number of solvent molecules required to trap the excess electron.

show abstract

Section: Resultsmentioning

confidence: 99%

Role of ab initio calculations in elucidating properties of hydrated and ammoniated electrons

Newton¹

1975

J. Phys. Chem.

186

View full text Add to dashboard Cite

show abstract

“…33,36,37 To minimize the light loss due to the infrared absorption of water, D 2 O was used instead of H 2 O. 39 In Fig. The signals were amplified 25-100 times by a BX-31A wide band preamplifier ͑NF Electronic Instruments͒ before sending to a digital oscilloscope that was connected to a computer through a GPIB interface.…”

Section: Methodsmentioning

confidence: 99%

Effect of water density on the absorption maximum of hydrated electrons in sub- and supercritical water up to 400 °C

Jay‐Gerin

Lin

Katsumura

et al. 2008

The Journal of Chemical Physics

View full text Add to dashboard Cite

The optical absorption spectra of the hydrated electron (e(aq) (-)) in supercritical (heavy) water (SCW) are measured by electron pulse radiolysis techniques as a function of water density at three temperatures of 380, 390, and 400 degrees C, and over the density range of approximately 0.2-0.65 g/cm(3). In agreement with previous work, the position of the e(aq) (-) absorption maximum (E(A(max) )) is found to shift slightly to lower energies (spectral "redshift") with decreasing density. A comparison of the present E(A(max) )-density data with other measurements already reported in the literature in subcritical (350 degrees C) and supercritical (375 degrees C) water reveals that at a fixed pressure, E(A(max) ) decreases monotonically with increasing temperature in passing through the phase transition at t(c). By contrast, at constant density, E(A(max) ) exhibits a minimum as the water passes above the critical point into SCW. These behaviors are explained in terms of simple microscopic arguments based on the crucial role played by local density and configurational fluctuations (associated with criticality) in providing pre-existing polymeric clusters, which act as trapping sites for electrons.

show abstract

“…Therefore, prior to carrying out femtosecond experiments on the recombination dynamics, detailed information is required on the spectral position of the ammoniated electron’s absorption band as a function of temperature and density. Fortunately, throughout almost the entire temperature and density range studied here, such data are available from experiments conducted by Schindewolf and co-workers many years ago. − Interestingly, at high temperatures and pressures, the stationary absorption of ammoniated electrons is reported to be barely sensitive to the thermodynamic conditions. At T ≥ 294 K, our probe wavelength was set to 1760 nm, whereas for lower temperatures the probe pulses had to be tuned to 1450 nm.…”

Section: Resultsmentioning

confidence: 94%

Femtosecond Two-Photon Ionization and Solvated Electron Geminate Recombination in Liquid-to-Supercritical Ammonia

et al. 2012

View full text Add to dashboard Cite

The first-ever femtosecond pump-probe study is reported on solvated electrons that were generated by multiphoton ionization of neat fluid ammonia. The initial ultrafast ionization was carried out with 266 nm laser pulses and was found to require two photons. The solvated electron was detected with a femtosecond probe pulse that was resonant with its characteristic near-infrared absorption band around 1.7 μm. Furthermore, the geminate recombination dynamics of the solvated electron were studied over wide ranges of temperature (227 K ≤ T ≤ 489 K) and density (0.17 g cm(-3) ≤ ρ ≤ 0.71 g cm(-3)), thereby covering the liquid and the supercritical phase of the solvent. The electron recombines in a first step with ammonium cations originating from the initial two-photon ionization thereby forming transient ion-pairs (e(am)(-)·NH(4)(+)), which subsequently react in a second step with amidogen radicals to reform neutral ammonia. The escape probability, i.e., the fraction of solvated electrons that can avoid the geminate annihilation, was found to be in quantitative agreement with the classical Onsager theory for the initial recombination of ions. When taking the sequential nature of the ion-pair-mediated recombination mechanism explicitly into account, the Onsager model provides a mean thermalization distance of 6.6 nm for the solvated electron, which strongly suggests that the ionization mechanism involves the conduction band of the fluid.

show abstract

ChemInform Abstract: STABILITAETSGRENZE SOLVATISIERTER ELEKTRONEN IN SUPERKRITISCHEM AMMONIAK IM BEREICH GERINGER DICHTE

Abstract: Pulsradiolyse von überkritischem Ammoniak führt im Dichtebereich des Lösungsmittels bis hinab zu lO mol/l zu solvatisierten Elektronen, deren Absorptionsspektrum in Form und Lage ungefähr übereinstimmt mit dem in flüssigem Ammoniak bei tiefen Temperaturen.

Cited by 4 publications

References 1 publication

Role of ab initio calculations in elucidating properties of hydrated and ammoniated electrons

Role of ab initio calculations in elucidating properties of hydrated and ammoniated electrons

Effect of water density on the absorption maximum of hydrated electrons in sub- and supercritical water up to 400 °C

Femtosecond Two-Photon Ionization and Solvated Electron Geminate Recombination in Liquid-to-Supercritical Ammonia

Contact Info

Product

Resources

About