The roles of the solute and solvent cavities in charge-transfer-to-solvent dynamics: Ultrafast studies of potasside and sodide in diethyl ether

Journal Article · Tue Oct 07 04:00:00 EDT 2008 · Journal of Chemical Physics

DOI:https://doi.org/10.1063/1.2977995· OSTI ID:21254770

Cavanagh, Molly C; Young, Ryan M; Schwartz, Benjamin J ^[1]

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1. Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095-1569 (United States)

Although electron transfer reactions are among the most fundamental in chemistry, it is still not clear how to isolate the roles of the solute and solvent in moving charge between reactants in solution. In this paper, we address this question by comparing the ultrafast charge-transfer-to-solvent (CTTS) dynamics of potasside (K{sup -}) in diethyl ether (DEE) to those of sodide (Na{sup -}) in both DEE and tetrahydrofuran (THF). We find that for sodide in both DEE and THF, CTTS excitation leads to delayed ejection of a solvated electron that appears with its equilibrium absorption spectrum. This indicates that the ejected electrons are localized in pre-existing solvent traps, suggesting that the structure of liquid DEE is characterized by cavities that are favorably polarized to localize an excess electron, as has been previously shown is the case for liquid THF. We also find that the geminate recombination dynamics following CTTS excitation of sodide in THF and DEE are similar, suggesting that the nature of the CTTS excited states and their coupling to the electronic states supported by the naturally occurring solvent cavities are similar in the two solvents. In contrast, the geminate recombination dynamics of potasside and sodide in DEE are different, with red-edge excitation of the K{sup -} CTTS band producing a greater number of long-lived electrons than is seen following the corresponding red-edge excitation of the Na{sup -} CTTS band. This indicates that the CTTS excited states of K{sup -} are better able to couple to the electronic states supported by the naturally occurring solvent cavities, allowing us to compare the energetic positions of the potasside and sodide ground and CTTS excited states on a common absolute scale. Finally, we also observe a strong transient absorption following the CTTS excitation of potasside in DEE that correlates well with the 766 nm position of the gas-phase potassium D-line. The data indicate that CTTS excitation of alkali metal anions essentially instantaneously produces a gas-phase-like neutral alkali metal atom, which then spontaneously undergoes partial ejection of the remaining valence electron to form a neutral alkali metal cation:solvated electron tight-contact pair.

• OSTI ID: 21254770
• Journal Information: Journal of Chemical Physics, Journal Name: Journal of Chemical Physics Journal Issue: 13 Vol. 129; ISSN JCPSA6; ISSN 0021-9606
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
ABSORPTION SPECTRA
ELECTRON TRANSFER
ETHYL ETHER
EXCITATION
EXCITED STATES
POTASSIUM
POTASSIUM COMPOUNDS
POTASSIUM IONS
SODIUM COMPOUNDS
SODIUM IONS
SOLVATED ELECTRONS
SOLVENTS
TETRAHYDROFURAN