Ion chemistry in gaseous discharges at atmospheric pressure

The role of ions in plasma chemistry is briefly reviewed on the basis of recent literature reports. In addition, different chemical processes induced by gaseous discharges at atmospheric pressure are discussed here, with particular emphasis on the elucidation of some aspects of the ion chemistry occurring in benzene/air dielectric barrier and corona discharges. Through a multi-technique approach relying on gas chromatographic, mass spectrometric, spectroscopic and computational analyses, we have been able to reveal subtle mechanistic aspects involved in the ionic processes leading to the synthesis of covalent adducts. In particular, we report here the experimental conditions and the thermochemical reasons whereby we can access the synthesis (i) of benzenediazonium ion C6H5N2+ from the reaction of phenylium ion C6H5+ with N2, (ii) of protonated biphenyl ions C12H11+ from electrophilic aromatic attack of phenylium ion on C6H6, (iii) of phenol radical cations C6H5OH+. via O radical addition on the benzene ring followed by ionization of the neutral product and finally (iv) of biphenyl-oxonium ions C12H11O+ and hydroxylbiphenyl-oxonium ions C12H11O2+ as end-products of the electrophilic attack of phenol ions on benzene and phenol, respectively. Finally, intriguing chemical paths involved in the corona discharge ionization of acetonitrile are also discussed.