Oxygen reactions in high-pressure nitrogen gas studied with optical emission spectroscopy

A study of some oxygen reactions in irradiated high-pressure (0.34–3.3 MPa) nitrogen gas is presented. Nitrogen gas containing 1 ppm H2O and O2 was irradiated in a closed target chamber with 4.3 MeV protons. Optical emission spectra of the NO-γ (A2Σ+–X2Π), the NO-β (B2Π–X2Π) and the O (1S–1D) transitions were recorded as a function of irradiation time at four different nitrogen-gas pressures. The results show a coupling between the NO-γ build-up half time and the NO-β decay and the O (1S–1D) decay half times as a function of irradiation time. The binding of free atomic oxygen in reactions forming NO has implications for the balance of [11C]CO2 versus [11C]CO production.