Comprehensive analysis of strong-field ionization and dissociation of diatomic nitrogen

Abstract

Accurate potential-energy curves are used consistently instead of Coulombic curves to determine the internuclear separation at ionization, ${R}_{\mathrm{ion}},$ in a strong laser field, for charge states of ${\mathrm{N}}_{2}$ up to ${\mathrm{N}}_{2}^{5+}.$ Furthermore, we exlude the kinetic energy gained from previous ionization steps in determining ${R}_{\mathrm{ion}}.$ With these improvements, we analyze various dissociation pathways from ${\mathrm{N}}_{2}^{2+}$ to ${\mathrm{N}}_{2}^{5+}$ and find that the charge symmetric pathways do not give physical results. In fact, it appears that all ionization up to ${\mathrm{N}}_{2}^{5+}$ involves the charge asymmetric channel ${\mathrm{N}}_{2}^{4+}\ensuremath{\rightarrow}{\mathrm{N}}^{+}+{\mathrm{N}}^{3+}.$ By determining the time between each ionization step, we observe the competition between laser intensity and internuclear separation in determining the molecular ionization rate. Finally, our data are consistent with recent observations that short pulse (130 fs) ionization leaves fragments in electronically excited states whereas long pulse (>600 fs) ionization leaves them in ground electronic states.