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

David Grills, Sergei V. Lymar

Research output: Contribution to journalArticle

2 Citations (Scopus)

Abstract

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.

Original languageEnglish
Pages (from-to)10011-10017
Number of pages7
JournalPhysical Chemistry Chemical Physics
Volume20
Issue number15
DOIs
Publication statusPublished - Jan 1 2018

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Carbon Dioxide
acetonitrile
Anions
carbon dioxide
Infrared spectroscopy
formic acid
anions
spectroscopy
Radiolysis
Reducing Agents
Scavenging
Discrete Fourier transforms
Labeling
Protons
Absorption spectra
Rate constants
Experiments
Radiation
Atoms
Electrons

ASJC Scopus subject areas

  • Physics and Astronomy(all)
  • Physical and Theoretical Chemistry

Cite this

Radiolytic formation of the carbon dioxide radical anion in acetonitrile revealed by transient IR spectroscopy. / Grills, David; Lymar, Sergei V.

In: Physical Chemistry Chemical Physics, Vol. 20, No. 15, 01.01.2018, p. 10011-10017.

Research output: Contribution to journalArticle

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