Highly monochromatized electrons (with 30 meV FWHM) are used in a crossed beam experiment to investigate electron attachment to oxygen clusters $({\mathrm{O}}_2{)}_n$ at electron energies from approximately 0 to 2 eV. At energies close to zero, the attachment cross section for the reaction $({\mathrm{O}}_2{)}_n+e\to {\mathrm{O}}_2^{-}$ rises strongly with decreasing electron energy compatible with $s$-wave electron capture to $({\mathrm{O}}_2{)}_n$. Peaks in the attachment cross section present at higher energies can be ascribed to vibrational levels of the oxygen anion. The vibrational spacings observed can be quantitatively accounted for by model calculations.

• Received 21 March 1996

DOI:https://doi.org/10.1103/PhysRevLett.77.3771