Post Discharge Chemistry of Aromatic Molecules in Rare Gas

We have employed 800 nm 150 fs laser pulses to carry out photoionization (PI) time-of-flight mass spectrometric detection of intermediates following corona discharges on aromatic molecules (alkylbenzenes and pyridine) in He, stabilized by subsequent supersonic gas expansions. Observed product peaks appear to be at least roughly in proportion to actual number densities; PI induced fragmentation of parent ions appears not to be excessive. Consequently, 800 nm fs PI should be useful for general product analysis applications in plasma chemistry. For most alkylbenzenes subjected to corona discharges in rare gas, the overall trends in product chemistry are similar in many respects to observed flame and pyrolysis chemistry in rare gases for the same species. Following discharge, as in those other cases, H deficient carbon radical fragments initially produced react in turn to form larger aromatic species. However, compared with flame/pyrolysis, discharge produced a larger number of fragment species, which can lead to a wider and somewhat different range of higher mass aromatic products. Co-addition of even a small component of O₂ to the discharge mixes has a potent effect in inhibiting formation of higher mass aromatic products in alkylbenzenes.