Laser-induced Coulomb explosion of the LiI molecule and of its dimer

Abstract

A gas-phase sample consisting of lithium iodide, $\mathrm{LiI}$, molecules and their dimer ${(\mathrm{LiI})}_2$, are Coulomb exploded by an intense 25 femtosecond laser pulse. In the case of $\mathrm{LiI}$, we focus on the double ionization that creates a pair of ${\mathrm{Li}}^{+}$ and ${\mathrm{I}}^{+}$ recoil ions. From the kinetic energy distribution of the ${\mathrm{Li}}^{+}$ ions, extracted using coincidence filtering, we determine the distribution of internuclear distances $P(R)$ via the ground state potential curve of ${\mathrm{LiI}}^{2+}$ obtained from an ab initio calculation that accounts for non-Coulombic effects. We find that the center of $P(R)$ is close to the expected internuclear separation based on the three vibrational states of $\mathrm{LiI}$ populated, whereas the width of $P(R)$ exceeds the theoretical value by $\sim$ 52 %. We discuss if fragmentation via excited ${\mathrm{LiI}}^{2+}$ potential curves affects the determination of $P(R)$. In the case of the dimer, ${(\mathrm{LiI})}_2$, we observe kinetic energies and relative emission directions of ${\mathrm{Li}}^{+}$, ${\mathrm{I}}^{+}$, and ${\mathrm{I}}^{2+}$ recoil ions consistent with Coulomb explosion of the parallelogram-shaped dimer after removing up to six electrons by the laser pulse.

14 pages, 7 figures