Threshold photoelectrons coincidence spectroscopy of doubly-charged ions of nitrogen, carbon monoxide, nitric oxide and oxygen

Single photon double ionization of nitrogen (N 2 ), carbon monoxide (CO), nitric oxide (NO) and oxygen (O 2 ) has been studied in an electron-electron coincidence experiment. Threshold photoelectrons coincidence (TPEsCO) spectra have been obtained using a dual penetrating field technique, in which only electrons with nearly zero kinetic energy (<20 meV) are detected. The high sensitivity and energy resolution attainable have allowed observation of several states of N 2 2+ , CO 2+ , NO 2+ and O 2 2+ , excited essentially at their respective thresholds, resolving vibrational energy levels for nearly all states where they exist. Accurate energies of the features observed in the TPEsCO spectra, and the molecular parameters derived from them, are presented, and the possible mechanisms of formation are discussed.