Ultrafast predissociation of superexcited nitrogen molecules

Superexcited states of neutral nitrogen molecules, with excited N-2(+) (C-2 Sigma(+)(u)) ion cores, are prepared above the N-2 ionization limit with femtosecond pulses of 23.1 eV photons, produced by high-order harmonic generation. Time-resolved predissociation of the superexcited nitrogen molecules is observed by detection of electronically excited atomic N*(4p) and/or N*(3d) product formation, by photoionization of the excited atoms with a delayed 805 nm pulse. An upper limit lifetime of 25 fs is determined for the superexcited states, attributed to the sum of autoionization and predissociation pathways, based on the risetime of predissociation products. The observation of dissociation products from the short-lived states shows that the predissociation decay pathways compete with autoionization pathways on an ultrafast timescale.