Quantum interference scattering of aligned molecules: Bonding in O-4 and role of spin coupling

Molecular beam experiments on collisions between oxygen molecules were perf ormed at low energy and high angular resolution to permit observation of th e "glory" interference effect. A novel technique for aligning the rotationa l angular momentum of the colliding molecules is exploited. Analysis of tot al scattering cross section data yields for the O-2-O-2 bond an energy of 1 .65 +/- 0.08 kJ.mol(-1) for the most stable configuration (parallel molecul es) at a distance of 0.356 +/- 0.007 nm. These results indicate that most o f the bonding in the dimer comes from electrostatic (van der Weals) farces but chemical (spin-spin) contributions are not negligible. [S0031-9007(98)0 8079-X].