Two-directional collisional energy exchange between electrons and ions in exploding clusters

We present the results of theoretical–computational studies of inter-particle energy transfer caused by elastic electron–ion collisions in expanding $$(\hbox {H}^{+})_{\mathrm {N}} +$$ electrons and $$\left( \mathrm {N}\mathrm {e}^{{8+}} \right) _{\mathrm {N}} +$$ electrons nanoplasmas, which are produced from clusters driven by near-infrared femtosecond, intense laser pulses. In these nanoplasmas, the short-range part of the electron–ion interactions is attractive for the $$\hbox {H}^{+}$$ ions and repulsive for the $$\mathrm {N}\mathrm {e}^{{8+}}$$ ions. The electron–ion collision times are ultrashort with $$\uptau = 10-20$$ as (attoseconds) for $$\left( \mathrm {N}\mathrm {e}^{\mathrm {8+}} \right) _{\mathrm {N}} +$$ electrons nanoplasmas and $$\uptau = 10$$–50 as for ($$\hbox {H}^{+})_{\mathrm {N}} +$$ electrons nanoplasmas. The collisional inter-particle energy transfers (CIET) are two-directional, occurring either from an electron to an ion or vice versa. The magnitude of the separate energy transfer processes depends on the kinetic energies of both colliding particles as well as on the collision geometry. While our previous studies dealt with periphery ions, the present work considers the collisional energy transfer within the entire clusters, where the relation between electron to ion and ion to electron energy transfers was found to be close to balance, providing on average a low net collisional energy transfer to ions. In the clusters’ inner cores this energy transfer presents 2–4% of the final ion energies in the $$\left( \mathrm {N}\mathrm {e}^{\mathrm {8+}} \right) _{\mathrm {N}}$$ clusters and less than 1% in the $$\left( \mathrm {H}^{+} \right) _{\mathrm {N}}$$ clusters, being lower in the clusters’ outer shells. Our findings provide strong evidence for the absence of the so called hydrodynamic expansions and for the dominance of Coulomb interactions in the explosion of the cluster nanoplasmas