RYDBERG-ATOM COLLISIONS WITH SF6 AND CCL4 AT VERY HIGH N

Rate constants for Rydberg-atom destruction through electron transfer in collisions between K(np) Rydberg atoms and SF6 and CCl4 have been measured for values of principal quantum number n up to n approximately 400 using an apparatus specifically developed for very-high-n collision studies. Analysis of the data using the free-electron model provides cross sections for electron attachment to SF6 and CCl4 at electron energies down to approximately 10-mu-eV, which are far below those accessible using any alternate technique. The measured cross sections are inversely proportional to electron velocity and are consistent with the Wigner threshold law for s-wave attachment.