The vibrationally inelastic scattering of Rydberg H atoms $(n=30\mathrm{}–50)$ from $\mathrm{N}{}_2$ and $\mathrm{O}{}_2$ at $E_{\mathrm{coll}}=1.84\mathrm{eV}$ was studied as a function of laboratory deflection angle. On average, 4 times more vibrational excitation was observed in collisions with $\mathrm{O}{}_2$ than with $\mathrm{N}{}_2$. Vibrational excitation of $\mathrm{O}{}_2$ results largely from collisions in which an electron is briefly transferred from $\mathrm{O}{}_2$ to the proton core, while the Rydberg electron remains a spectator. This provides further evidence that the free electron model applies to low energy collisions involving the ionic core leading to substantial momentum transfer.

• Received 11 October 2000

DOI:https://doi.org/10.1103/PhysRevLett.86.3997