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. ${\mathrm{Ne}}^{+}$, ${\mathrm{Ar}}^{+}$, and ${\mathrm{Xe}}^{+}$, 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 ${\mathrm{Na}}^{+}$ 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 ṽ=0.8–3.7 times the Bohr orbital velocity of the target atoms. The n dependence was measured at reduced velocity ṽ=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 ${\mathrm{H}}^{+}$+H(1s) collisions at projectile energies 16–340 keV.