Quantum Interference Scattering of Aligned Molecules: Bonding in $O_4$ and Role of Spin Coupling

Molecular beam experiments on collisions between oxygen molecules were performed at low energy and high angular resolution to permit observation of the “glory” interference effect. A novel technique for aligning the rotational angular momentum of the colliding molecules is exploited. Analysis of total scattering cross section data yields for the ${\mathrm{O}}_2-{\mathrm{O}}_2$ bond an energy of $1.65\pm 0.08\mathrm{kJ}̇{\mathrm{mol}}^{-1\mathrm{}}$ for the most stable configuration (parallel molecules) at a distance of $0.356\pm 0.007\mathrm{nm}$. These results indicate that most of the bonding in the dimer comes from electrostatic (van der Waals) forces but chemical (spin-spin) contributions are not negligible.