TY - JOUR
T1 - Radiolytic formation of the carbon dioxide radical anion in acetonitrile revealed by transient IR spectroscopy
AU - Grills, David C.
AU - Lymar, Sergei V.
N1 - Funding Information:
This work, and use of the LEAF and Van de Graaff facilities of the Accelerator Center for Energy Research at BNL, was supported by the U.S. Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences & Biosciences under contract DE-SC0012704. We thank Mr Bobby Layne for technical support in the design and construction of TRIR detection systems.
PY - 2018
Y1 - 2018
N2 - The solvated electron in CH3CN is scavenged by CO2 with a rate constant of 3.2 × 1010 M-1 s-1 to produce the carbon dioxide radical anion (CO2-), 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 CO2- stretch. This assignment is confirmed by 13C isotopic labelling experiments and DFT calculations. In neat CH3CN, CO2- decays on a ∼10 μs time scale via recombination with solvent-derived radicals (R) and solvated protons. Upon addition of formate (HCO2-), the radiation yield of CO2- is substantially increased due to H-atom abstraction by R from HCO2- (R + HCO2- → RH + CO2-), which occurs in two kinetically separated steps. The rapid step involves the stronger H-abstracting CN, CH3, and possibly, H primary radicals, while the slower step is due to the less reactive, but more abundant radical, CH2CN. The removal of solvent radicals by HCO2- also results in over a hundredfold increase in the CO2- lifetime. CO2- scavenging experiments suggest that at 50 mM HCO2-, about 60% of the solvent-derived radicals are engaged in CO2- generation. Even under CO2 saturation, no formation of the radical adduct, (CO2)2-, could be detected on the microsecond time scale.
AB - The solvated electron in CH3CN is scavenged by CO2 with a rate constant of 3.2 × 1010 M-1 s-1 to produce the carbon dioxide radical anion (CO2-), 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 CO2- stretch. This assignment is confirmed by 13C isotopic labelling experiments and DFT calculations. In neat CH3CN, CO2- decays on a ∼10 μs time scale via recombination with solvent-derived radicals (R) and solvated protons. Upon addition of formate (HCO2-), the radiation yield of CO2- is substantially increased due to H-atom abstraction by R from HCO2- (R + HCO2- → RH + CO2-), which occurs in two kinetically separated steps. The rapid step involves the stronger H-abstracting CN, CH3, and possibly, H primary radicals, while the slower step is due to the less reactive, but more abundant radical, CH2CN. The removal of solvent radicals by HCO2- also results in over a hundredfold increase in the CO2- lifetime. CO2- scavenging experiments suggest that at 50 mM HCO2-, about 60% of the solvent-derived radicals are engaged in CO2- generation. Even under CO2 saturation, no formation of the radical adduct, (CO2)2-, could be detected on the microsecond time scale.
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U2 - 10.1039/c8cp00977e
DO - 10.1039/c8cp00977e
M3 - Article
C2 - 29620127
AN - SCOPUS:85045846391
VL - 20
SP - 10011
EP - 10017
JO - Physical Chemistry Chemical Physics
JF - Physical Chemistry Chemical Physics
SN - 1463-9076
IS - 15
ER -