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

A gas-phase sample consisting of lithium iodide, LiI, molecules and their dimer (LiI)₂, are Coulomb exploded by an intense 25 femtosecond laser pulse. In the case of LiI, we focus on the double ionization that creates a pair of Li⁺ and I⁺ recoil ions. From the kinetic energy distribution of the Li⁺ ions, extracted using coincidence filtering, we determine the distribution of internuclear distances $P(R)$ via an ab initio calculated potential energy curve for LiI²⁺, 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 LiI populated, whereas the width of $P(R)$ exceeds the theoretical value by ~ 55 %. We discuss why Coulomb explosion imaging of this system works well despite LiI²⁺ possibly fragmenting via multiple potential energy curves. In the case of the dimer, (LiI)₂, we observe kinetic energies and relative emission directions of Li⁺, I⁺, and I²⁺ recoil ions consistent with Coulomb explosion of the parallelogram-shaped dimer after removing up to six electrons by the laser pulse.