Near-threshold photoionisation studies of N2

Photoionisation of N2 to the nu =0, 1 and 2 vibrational levels of the X 2 Sigma g+ state of N2+, over the photon energy range from 15.5 to 18.0 eV has been studied in two ways. Firstly the threshold photoelectron spectrum has been obtained with a threshold resolution of approximately 3 meV, using a new threshold analyser. Secondly the relative partial photoionisation cross sections for the nu =0, 1 and 2 vibrational levels of the X 2 Sigma g+ state have been measured, using a technique in which the photon energy is varied continuously while the collection energy of the photoelectron analyser is changed in synchronism. The partial photoionisation cross sections show much structure due to the existence of autoionising states, and give information on the decay of these autoionising states into the vibrational levels of the X 2 Sigma g+ ion state.