Radiative lifetimes of metastable O+2(a 4Πu) and NO+(a 3Σ+)

The spin-forbidden radiative decays of the lowest energy metastable electronic states of O+2 and NO+ have been studied using a Fourier transform ion cyclotron resonance mass spectrometer. The metastable species are stored in the mass spectrometer for several hundreds of milliseconds and then selectively detected by pulsing CO2 into the ion trap and monitoring the formation of CO+2. By varying the delay time between formation of the metastable ions and injection of CO2, apparent radiative lifetimes of 101 ms for O+2(a 4Πu) and 530 ms for NO+(a 3Σ+) are measured. Our results are compared with literature values and with a theoretical calculation. The theoretical model, demonstrated for O+2, is based on spin–orbit coupling between the a 4Πu and A2Πu states and upon spin–rotation mixing of the different spin components within the a 4Πu state. The results allow quantitative interpretation of our results and those available in the literature.