dorsal/arxiv
View SchemaUltrafast Dynamics for Electron Photodetachment from Aqueous Hydroxide
| Authors | Robert A. Crowell, Rui Lian, Ilya A. Shkrob, David M. Bartels, Xiyi Chen, Stephen E. Bradforth |
|---|---|
| Categories | |
| ArXiv ID | physics/0401071 |
| URL | https://arxiv.org/abs/physics/0401071 |
| DOI | 10.1063/1.1739213 |
Abstract
Charge-transfer-to-solvent (CTTS) reactions of hydroxide induced by 200 nm monophotonic or 337 nm and 389 nm biphotonic excitation of this anion in aqueous solution have been studied by means of pump-probe ultrafast laser spectroscopy. Transient absorption kinetics of the hydrated electron, eaq-, have been observed, from a few hundred femtoseconds out to 600 ps, and studied as function of hydroxide concentration and temperature. The geminate decay kinetics are bimodal, with a fast exponential component (ca. 13 ps) and a slower power "tail" due to the diffusional escape of the electrons. For the biphotonic excitation, the extrapolated fraction of escaped electrons is 1.8 times higher than for the monophotonic 200 nm excitation (31% vs. 17.5% at 25 oC, respectively), due to the broadening of the electron distribution. The biphotonic electron detachment is very inefficient; the corresponding absorption coefficient at 400 nm is < 4 cm TW-1 M-1 (assuming unity quantum efficiency for the photodetachment). For [OH-] between 10 mM and 10 M, almost no concentration dependence of the time profiles of solvated electron kinetics was observed. At higher temperature, the escape fraction of the electrons increases with a slope of 3x10-3 K-1 and the recombination and diffusion-controlled dissociation of the close pairs become faster. Activation energies of 8.3 and 22.3 kJ/mol for these two processes were obtained. The semianalytical theory of Shushin for diffusion controlled reactions in the central force field was used to model the geminate dynamics. The implications of these results for photoionization of water are discussed.
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"abstract": "Charge-transfer-to-solvent (CTTS) reactions of hydroxide induced by 200 nm\nmonophotonic or 337 nm and 389 nm biphotonic excitation of this anion in\naqueous solution have been studied by means of pump-probe ultrafast laser\nspectroscopy. Transient absorption kinetics of the hydrated electron, eaq-,\nhave been observed, from a few hundred femtoseconds out to 600 ps, and studied\nas function of hydroxide concentration and temperature. The geminate decay\nkinetics are bimodal, with a fast exponential component (ca. 13 ps) and a\nslower power \"tail\" due to the diffusional escape of the electrons. For the\nbiphotonic excitation, the extrapolated fraction of escaped electrons is 1.8\ntimes higher than for the monophotonic 200 nm excitation (31% vs. 17.5% at 25\noC, respectively), due to the broadening of the electron distribution. The\nbiphotonic electron detachment is very inefficient; the corresponding\nabsorption coefficient at 400 nm is \u003c 4 cm TW-1 M-1 (assuming unity quantum\nefficiency for the photodetachment). For [OH-] between 10 mM and 10 M, almost\nno concentration dependence of the time profiles of solvated electron kinetics\nwas observed. At higher temperature, the escape fraction of the electrons\nincreases with a slope of 3x10-3 K-1 and the recombination and\ndiffusion-controlled dissociation of the close pairs become faster. Activation\nenergies of 8.3 and 22.3 kJ/mol for these two processes were obtained. The\nsemianalytical theory of Shushin for diffusion controlled reactions in the\ncentral force field was used to model the geminate dynamics. The implications\nof these results for photoionization of water are discussed.",
"arxiv_id": "physics/0401071",
"authors": [
"Robert A. Crowell",
"Rui Lian",
"Ilya A. Shkrob",
"David M. Bartels",
"Xiyi Chen",
"Stephen E. Bradforth"
],
"categories": [
"physics.chem-ph"
],
"doi": "10.1063/1.1739213",
"title": "Ultrafast Dynamics for Electron Photodetachment from Aqueous Hydroxide",
"url": "https://arxiv.org/abs/physics/0401071"
},
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