Structures of N ₂Ar, O ₂Ar, and O ₂Xe dimers studied by Coulomb explosion imaging

We use intense femtosecond laser pulses to multiply ionize and directly image the structures of N ₂Ar, O ₂Ar, and O ₂Xe 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 R _N2-Ar ∼ 3.86 Å, R _O2-Ar ∼ 3.65 Å, and R _O2-Xe ∼ 4.07 Å, respectively. For the T-shaped N ₂Ar dimer, both sequential and direct triple-ionization-induced three-body breakups are observed. In contrast to N ₂Ar dimer, other structures are found to coexist with the dominating T-shaped one for O ₂Ar and O ₂Xe.