Oxygen radiolysis by modulated molecular beam mass spectrometry

An experimental system for on-line mass spectrometric analysis of gas phase radiolysis systems was developed. Oxygen in a fast flow reaction tube was irradiated with 1 MeV protons and subsequently sampled with a molecular beam source. Analysis of the modulated molecular beam with a quadrupole mass spectrometer provided the concentrations of O, O2, and O3 as functions of reaction time, dose rate, and system pressure. Observed ozone levels were anomalously high compared to the predictions of existing chemical models, with apparent g values considerably above theoretical maximum values. Agreement of theory with the data was improved by postulating an excited state of O2 as a direct precursor to ozone