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Title: Radiolytic formation of the carbon dioxide radical anion in acetonitrile revealed by transient IR spectroscopy

In this study, the solvated electron in CH 3CN is scavenged by CO 2 with a rate constant of 3.2 × 10 10 M –1 s –1 to produce the carbon dioxide radical anion (CO 2 •–), a strong and versatile reductant. Using pulse radiolysis with time-resolved IR detection, this radical is unambiguously identified by its absorption band at 1650 cm –1 corresponding to the antisymmetric CO 2 •– stretch. This assignment is confirmed by 13C isotopic labelling experiments and DFT calculations. In neat CH 3CN, CO 2 •– decays on a ~10 μs time scale via recombination with solvent-derived radicals (R•) and solvated protons. Upon addition of formate (HCO 2 ), the radiation yield of CO 2 •– is substantially increased due to H-atom abstraction by R• from HCO 2 (R• + HCO 2 → RH + CO 2 •–), which occurs in two kinetically separated steps. The rapid step involves the stronger H-abstracting CN•, CH 3•, and possibly, H• primary radicals, while the slower step is due to the less reactive, but more abundant radical, CH 2CN•. The removal of solvent radicals by HCO 2 also results in over a hundredfold increase in the COmore » 2 •– lifetime. CO 2 •– scavenging experiments suggest that at 50 mM HCO 2 , about 60% of the solvent-derived radicals are engaged in CO 2 •– generation. Finally, even under CO 2 saturation, no formation of the radical adduct, (CO 2) 2 •–, could be detected on the microsecond time scale.« less
Authors:
ORCiD logo [1] ;  [1]
  1. Brookhaven National Lab. (BNL), Upton, NY (United States). Chemistry Division
Publication Date:
Report Number(s):
BNL-203439-2018-JAAM
Journal ID: ISSN 1463-9076; PPCPFQ
Grant/Contract Number:
SC0012704
Type:
Accepted Manuscript
Journal Name:
Physical Chemistry Chemical Physics. PCCP (Print)
Additional Journal Information:
Journal Name: Physical Chemistry Chemical Physics. PCCP (Print); Journal ID: ISSN 1463-9076
Publisher:
Royal Society of Chemistry
Research Org:
Brookhaven National Laboratory (BNL), Upton, NY (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22). Chemical Sciences, Geosciences & Biosciences Division; USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY
OSTI Identifier:
1430880
Alternate Identifier(s):
OSTI ID: 1434142