Detection of Long-Lived Excited States of Molecules by Penning Ionization

A method for the detection of excited neutral long-lived particles by ionization of properly chosen molecules with different ionization potential was developed and applied to the study of long-lived excited states of H2, N2, CO, and O2. Results in H2 and O2 confirm previous findings. In N2 a new state was found which releases in the transition to the ground state an energy of ∼11.4–11.6 eV. Also determined was its separated excitation function. This state is formed partly through a resonance capture of an exciting electron and subsequent decomposition of the unstable negative excited molecular ion N2−*. In CO a new long-lived excited state at ∼10 eV was detected, and the existence of another, higher lying, state was suggested.