Structures of N₂Ar, O₂Ar, and O₂Xe dimers studied by Coulomb explosion imaging

We use intense femtosecond laser pulses to multiply ionize and directly image the structures of N2Ar, O2Ar, and O2Xe dimers by coincidently measuring the momenta of the fragment ions. All these dimers are found to have an equilibrium T-shaped structure in which the bond of the diatomic molecule is perpendicular to the dimer axis. The equilibrium distance between the rare-gas atom and the center-of-mass of the diatomic molecule is estimated to be RN2–Ar ∼ 3.86 Å, RO2–Ar ∼ 3.65 Å, and RO2–Xe ∼ 4.07 Å, respectively. For the T-shaped N2Ar dimer, both sequential and direct triple-ionization-induced three-body breakups are observed. In contrast to N2Ar dimer, other structures are found to coexist with the dominating T-shaped one for O2Ar and O2Xe.