Corona Discharge and Field Electron Emission in Ambient Air Using a Sharp Metal Needle: Formation and Reactivity of CO<sub>3</sub><sup>−•</sup> and O<sub>2</sub><sup>−•</sup>

Abstract

CO3−• and O2−• are known to be strong oxidizing reagents in biological systems. CO3−• in particular can cause serious damage to DNA and proteins by H• abstraction reactions. However, H• abstraction of CO3−• in the gas phase has not yet been reported. In this work we report on gas-phase ion/molecule reactions of CO3−• and O2−• with various molecules. CO3−• was generated by the corona discharge of an O2 reagent gas using a cylindrical tube ion source. O2−• was generated by the application of a 15 kHz high frequency voltage to a sharp needle in ambient air at the threshold voltage for the appearance of an ion signal. In the reactions of CO3−•, a decrease in signal intensities of CO3−• accompanied by the simultaneous increase of that of HCO3− was observed when organic compounds with H–C bond energies lower than ∼100 kcal mol−1 such as n-hexane, cyclohexane, methanol, ethanol, 1-propanol, 2-propanol, and toluene were introduced into the ion source. This clearly indicates the occurrence of H• abstraction. O2−• abstracts H+ from acid molecules such as formic, acetic, trifluoroacetic, nitric and amino acids. Gas-phase CO3−• may play a role as a strong oxidizing reagent as it does in the condensed phase. The major discharge product CO3−• in addition to O2−•, O3, and NOx• that are formed in ambient air may cause damage to biological systems.