Charge Asymmetric Dissociation Induced by Sequential and Nonsequential Strong Field Ionization

Abstract

Charge asymmetric dissociation (CAD) is observed, for the first time, with near-infrared 30 fs laser pulses, in small molecules, ${\mathrm{N}}_{2}$ and ${\mathrm{O}}_{2}$. ${\mathrm{N}}_{2}^{2+}$ is created by a nonsequential (vertical) transition and the dissociation fragments appear to be in excited states. Unlike ${\mathrm{N}}_{2}$, ${\mathrm{O}}_{2}^{2+}$ involves a sequential (nonvertical) transition. The charge asymmetric dipole coupling to the external field is insufficient to populate the charge transfer states leading to CAD. Rather, CAD is a natural result of strong field excitation and ionization. These results in the tunneling regime are also compared with previous experiments performed with UV radiation in the multiphoton regime.