Abstract

A new transition at 55.8 nm (22.2 eV) has been observed in ${\text{N}}_2^{2+}$arising from multiphoton excitation of N₂ with intense subpicosecond 248-nm radiation. The band has an observed width of ~ 0.3 nm FWHM, exhibits vibrational splittings, has an estimated radiative lifetime of ~ 100 ps, and is attributed to a ³Π_u→ ³Π_g excimer-like transition arising from the direct multiphoton production of molecular levels having a 2σ_g vacancy. The upper level has a $\left(2{\sigma }_g{}^{-1},1{\pi }_u^{-1}\right)$ configuration, an equilibrium internuclear separation of ~ 1.2 Å, and results from an entirely new strong-field mode of electronic excitation.

© 1989 Optical Society of America