Coulomb explosion of nitrogen and oxygen molecules through non-Coulombic states

Abstract

We have systematically studied Coulomb explosion of nitrogen and oxygen molecules in intense 8 and 24 fs laser pulses. In the experiment, we explicitly separated all explosion pathways through coincident measurements. The high resolution kinetic energy releases (KERs) and the exotic angular distributions of atomic ions provide direct evidence that Coulomb explosion occurs through non-Coulombic states. In the theory, we calculated dissociation potential energy curves (PECs) of nitrogen and oxygen molecules and their multicharged molecular ions using multiconfiguration second-order perturbation theory. The results indicate that Coulomb potentials are close to the accurate PECs of multicharged molecular ions only when the internuclear distance is larger than 3 Å. In comparison with the experimental observations and the theoretical calculations, we determined the internuclear distance when Coulombic explosion occurs. It is near the equilibrium distance of the neutral molecules in the case of 8 fs laser pulses and expands gradually with the increase of the charge state of the molecular ions in the case of 24 fs laser pulses.

Dissociative ionization and Coulomb explosion of CH3I in intense femto second laser fields

“…It was inferred that CE occurs at a larger critical bond length R C due to bond softening induced by the laser field [10,15,16]. Various models have been developed to explain this reduction in Coulomb energy, for example, the two-step model [10], the Thomas-Fermi-Dirac (TFD) model [17], the charge transfer enhanced ionization (CREI) model [15,16,[18][19][20][21] and the Molecular Ammosov-Delone-Krainov (MO-ADK) model [22][23][24]. The temporal rise of the E-field amplitude laser pulse brings about a weakening of the binding energy of the valence electrons to the molecules.…”

Communication: Determining the structure of the N2Ar van der Waals complex with laser-based channel-selected Coulomb explosion

“…The results indicate that Coulomb potential approaches the ab initio potential closely when the internuclear distance is larger than 2.1 Å. 15,28 van der Waals bonds usually have large equilibrium internuclear distances. Thus Coulomb potential is accurate enough to describe the explosion dynamics of van der Waals bond.…”

“…[22][23][24][25][26][27][28] The results have demonstrated that the nuclear motion can be frozen for molecules in the process of multiple ionization by using ultrashort laser pulses. 14,25,28 Thus, the reconstructed structure of the molecular ion before explosion can represent the structure of the neutral precursor molecules when such ultrashort laser pulses are applied. In addition, we have carefully compared the Coulomb potential and the ab initio potential for describing the fragmentation dynamics of molecular ions.…”

“…Indeed, some experimental observations have shown that the internuclear distance could be stretched and the structure could be changed during the multiple ionization of molecules induced by intense laser fields. 13,14,28 If the molecular structure is modified during the ionization process, the reconstructed structural parameters will be associated with specific channels and thus exhibit channel-dependence. 13,14,28 However, our observation for the case of N 2 Ar is that the reconstructed structural parameters do not depend on the channel from which the molecular structure is reconstructed.…”

“…13,14,28 If the molecular structure is modified during the ionization process, the reconstructed structural parameters will be associated with specific channels and thus exhibit channel-dependence. 13,14,28 However, our observation for the case of N 2 Ar is that the reconstructed structural parameters do not depend on the channel from which the molecular structure is reconstructed. The channelindependence indicates that the nuclear motion is frozen during the interaction between the van der Waals complex and the ultrashort 25 fs laser pulse.…”