State-to-State Inelastic Scattering of O2 with Helium

Molecular oxygen (O-2) is extremely important for a wide variety of processes on and outside Earth. Indeed, O-2 He collisions are crucial to model O-2 abundance in space or to create ultracold O-2 molecules. A crossed molecular beam experiment to probe rotational excitation of O-2 due to helium collisions at energies of 660 cm(-1) is reported. Velocity map imaging was combined with state-selective detection of O-2(X-3 Sigma(-)(g)) by (2+1) resonance-enhanced multiphoton ionization. The obtained raw O-2(+) images were corrected from density to flux and the differential cross sections (DCS) were then extracted for six O-2 final states. Exact quantum mechanical calculations were also performed. A very good agreement between experimental and theoretical DCSs was found by using an initial O-2 beam population ratio of 80% for the first rotational state and 20% for the first excited state. The agreement demonstrates our ability to model inelastic processes between O-2 molecules and rare gas both theoretically and experimentally.