Electron loss from Na Rydberg atoms by ion impact

The absolute cross section for removal of Rydberg electrons from Na Rydberg atoms by impact of singly charged ions was measured. Ne+, Ar+, and Xe+, accelerated to energies 1--5 keV, bombarded a Na atomic-beam target that was laser excited to nd states, n = 30--45. Electron loss, the sum of ionization and charge transfer, was detected by collecting impact-produced Na+ from the target after 1--3 μs exposure to the projectile beam. The velocity dependence of the cross section was measured for n = 40 with projectile velocities v = 0.8--3.7 times the Bohr orbital velocity of the target atoms. The n dependence was measured at reduced velocity v = 2.0 for n = 30--45. A study of field ionization of higher collisionally excited states was made, and important corresponding corrections were applied to the data. The effects of collisional l change in the target and of l mixing due to applied, pulsed electric fields were noted. The absolute unnormalized cross section for n = 40 agreed with classical-trajectory calculations and with the classical binary-encounter approximation. The classically predicted n scaling of the cross section at fixed reduced velocity was directly demonstrated, and a scaling exponent 4.08 +- 0.07 between n = 1 and 45 was found. The results may be compared with H++H(1s) collisions at projectile energies 16--340 keV