Figure 1. Recorded mass spectra using acetate or nitrate for ionization.

The detected RO₂ radicals from the oxidation of α-pinene appear as adducts with the reagent ions. Signals of nitrate adducts (black) are shifted by three mass units compared to the corresponding acetate adduct signals (red). The spectra obtained with acetate ionization are offset by 1.5 s⁻¹ for more clarity. The reaction time in all experiments was 7.9 s. (a) Spectra obtained from α-pinene ozonolysis for identical conditions [O₃]=6.1 × 10¹¹ and [α-pinene]=1.0 × 10¹² molecules cm⁻³. Simultaneous O₃ and OH radical reaction takes place due to OH radical production from ozonolysis. (b) Spectra from the pure OH+α-pinene reaction using H₂O₂ photolysis for OH radical formation, [H₂O₂]∼1 × 10¹⁴ and [α-pinene]=5.0 × 10¹² molecules cm⁻³. The signal at nominal 309 Th (first isotope signal of the RO₂ radical) can be partly influenced by the corresponding hydroperoxide.