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 an ab initio calculated potential energy curve for $\mathrm{LiI}^{2+}$, which 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 $\sim$ 55 %. We discuss why Coulomb explosion imaging of this system works well despite $\mathrm{LiI}^{2+}$ possibly fragmenting via multiple potential energy curves. 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.