Initial vibrational state dependence of resonant excitation and ‘‘dissociative attachment’’ in electron–N2 scattering

A beam of vibrationally excited ground state nitrogen molecules has been generated using a microwave discharge. The effect of this vibrational energy on the different decay processes of the A 2Πu state of N−2 formed by electron impact in the 7–13 eV region has been studied using an electron-impact spectrometer. Firstly, the ’’boomerang’’ oscillations occuring in the excitation cross section of the A 3Σ+u levels increase in amplitude when the initial level is v=1. This effect, as well as the measured cross sections are well described by calculations using the local complex potential model. Secondly, the cross section ratio for the ’’dissociative attachment’’, process yielding unstable N−(3P) from the v=0 and 1 levels has been evaluated indicating that the vibrational energy has almost no effect. The calculations further indicate that this ratio only rises to 4 when going from v=0 to 4 which is in sharp contrast to H2 where, in the 4 eV region the same amount of vibrational energy increases the dissociative attachment cross section by a factor of 360.