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Title: Escape of anions from geminate recombination in THF due to charge delocalization

Abstract

Geminate recombination of 24 radical anions (M˙ ) with solvated protons (RH 2 +) was studied in tetrahydrofuran (THF) with pulse radiolysis. The recombination has two steps: (1) diffusion of M˙ and RH 2 + together to form intimate (contact and solvent separated) ion pairs, driven by Coulomb attraction; (2) annihilation of anions due to proton transfer (PT) from RH 2 + to M˙ . The non-exponential time-dependence of the geminate diffusion was determined. For all molecules protonated on O or N atoms the subsequent PT step is too fast (<0.2 ns) to measure, except for the anion of TCNE which did not undergo proton transfer. PT to C atoms was as slow as 70 ns and was always slow enough to be observable. A possible effect of charge delocalization on the PT rates could not be clearly separated from other factors. For 21 of the 24 molecules studied here, a free ion yield (71.6 ± 6.2 nmol J –1) comprising ~29% of the total, was formed. This yield of “Type I” free ions is independent of the PT rate because it arises entirely by escape from the initial distribution of ion pair distances without forming intimate ion pairs.more » Furthermore, three anions of oligo(9,9-dihexyl)fluorenes, F n˙ (n = 2–4) were able to escape from intimate ion-pairs to form additional yields of “Type II” free ions with escape rate constants near 3 × 10 6 s –1. These experiments find no evidence for an inverted region for proton transfer.« less

Authors:
 [1]; ORCiD logo [1];  [2];  [3];  [4]; ORCiD logo [1]
  1. Brookhaven National Lab. (BNL), Upton, NY (United States)
  2. Kyoto Institute of Technology, Kyoto (Japan)
  3. Department of Chemistry and Ames Laboratory (USDOE); Iowa State University; Ames; USA
  4. Iowa State Univ., Ames, IA (United States)
Publication Date:
Research Org.:
Brookhaven National Laboratory (BNL), Upton, NY (United States); Ames Laboratory (AMES), Ames, IA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1413138
Alternate Identifier(s):
OSTI ID: 1412781
Report Number(s):
BNL-114803-2017-JA; IS-J-9488
Journal ID: ISSN 1463-9076; PPCPFQ; R&D Project: CO037; KC0304030; TRN: US1800361
Grant/Contract Number:
SC0012704; AC02-98CH10886; AC02-07CH11358
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Physical Chemistry Chemical Physics. PCCP (Print)
Additional Journal Information:
Journal Name: Physical Chemistry Chemical Physics. PCCP (Print); Journal Volume: 19; Journal Issue: 48; Journal ID: ISSN 1463-9076
Publisher:
Royal Society of Chemistry
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; radiation chemistry; pulse radiolysis; oligofluorenes; Onsager escape; charge delocalization; ion recombination; ion pair

Citation Formats

Chen, Hung -Cheng, Cook, Andrew R., Asaoka, Sadayuki, Boschen, Jeffery S., Windus, Theresa L., and Miller, John R. Escape of anions from geminate recombination in THF due to charge delocalization. United States: N. p., 2017. Web. doi:10.1039/C7CP05880B.
Chen, Hung -Cheng, Cook, Andrew R., Asaoka, Sadayuki, Boschen, Jeffery S., Windus, Theresa L., & Miller, John R. Escape of anions from geminate recombination in THF due to charge delocalization. United States. doi:10.1039/C7CP05880B.
Chen, Hung -Cheng, Cook, Andrew R., Asaoka, Sadayuki, Boschen, Jeffery S., Windus, Theresa L., and Miller, John R. Fri . "Escape of anions from geminate recombination in THF due to charge delocalization". United States. doi:10.1039/C7CP05880B. https://www.osti.gov/servlets/purl/1413138.
@article{osti_1413138,
title = {Escape of anions from geminate recombination in THF due to charge delocalization},
author = {Chen, Hung -Cheng and Cook, Andrew R. and Asaoka, Sadayuki and Boschen, Jeffery S. and Windus, Theresa L. and Miller, John R.},
abstractNote = {Geminate recombination of 24 radical anions (M˙–) with solvated protons (RH2+) was studied in tetrahydrofuran (THF) with pulse radiolysis. The recombination has two steps: (1) diffusion of M˙– and RH2+ together to form intimate (contact and solvent separated) ion pairs, driven by Coulomb attraction; (2) annihilation of anions due to proton transfer (PT) from RH2+ to M˙–. The non-exponential time-dependence of the geminate diffusion was determined. For all molecules protonated on O or N atoms the subsequent PT step is too fast (<0.2 ns) to measure, except for the anion of TCNE which did not undergo proton transfer. PT to C atoms was as slow as 70 ns and was always slow enough to be observable. A possible effect of charge delocalization on the PT rates could not be clearly separated from other factors. For 21 of the 24 molecules studied here, a free ion yield (71.6 ± 6.2 nmol J–1) comprising ~29% of the total, was formed. This yield of “Type I” free ions is independent of the PT rate because it arises entirely by escape from the initial distribution of ion pair distances without forming intimate ion pairs. Furthermore, three anions of oligo(9,9-dihexyl)fluorenes, Fn˙– (n = 2–4) were able to escape from intimate ion-pairs to form additional yields of “Type II” free ions with escape rate constants near 3 × 106 s–1. These experiments find no evidence for an inverted region for proton transfer.},
doi = {10.1039/C7CP05880B},
journal = {Physical Chemistry Chemical Physics. PCCP (Print)},
number = 48,
volume = 19,
place = {United States},
year = {Fri Nov 24 00:00:00 EST 2017},
month = {Fri Nov 24 00:00:00 EST 2017}
}

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