Dissociative ionization of ${\mathrm{N}}_2$ induced by intense picosecond radiation has been studied. A two-step multiphonon model, based on ionization of ${\mathrm{N}}_2$ through vertical transitions and spontaneous dissociation of ${\mathrm{N}}_2^{\mathit{z}+}$ (Z≥2) via Coulomb and non-Coulombic potentials curves, is presented to explain the origin of the kinetic energies of atomic ions observed. The model predicts that dissociation occurs near the internuclear separation of the neutral, charge-asymmetric dissociation channels are important, and dissociation via Coulomb curves will only be observed for pulses with extremely short rise times.

• Received 24 August 1992

DOI:https://doi.org/10.1103/PhysRevLett.69.2646