Abstract
Measurements have been made of the cross sections for collisional quenching of highly excited rubidium nS (12<or=n<or=18) and nD3/2(9<or=n<or=13) states by ground-state rubidium. The experimental values are shown to be close to the geometrical cross section. The large magnitude of the quenching cross section mainly reflects the long range of the Rydberg electron-alkali interaction.