Observation of a new inner-orbital molecular transition at 55.8 nm in N22+ produced by multiphoton coupling

A new transition at 55.8 nm (22.2 eV) has been observed in N22+ arising from multiphoton excitation of N2 with intense subpicosecond 248-nm radiation. The band has an observed width of 0.3 nm full width at half maximum, exhibits vibrational splittings, has an estimated radiative lifetime of 100 ps, and is attributed to a u33 g excimerlike transition arising from the direct multiphoton production of molecular levels having a 2g vacancy. The upper level has a (2g-1, 1u-1) configuration, an equilibrium internuclear separation of 1.2 AI, and results from an entirely new strong-field mode of electronic excitation. © 1989 The American Physical Society.