Projectilendistributions following charge transfer ofAr+andNa+in a Na Rydberg target

The n distributions produced by charge transfer of ${\mathrm{Ar}}^{+}$ and ${\mathrm{Na}}^{+}$ ions in a target of Na(nl) Rydberg atoms were extensively measured at intermediate velocities. The 60–2100-eV ions bombarded a laser-excited atomic-beam target. The projectiles were neutralized by capture into Rydberg states of Ar and Na and were analyzed by field ionization in an inhomogeneous-field detector whose response over states and energies was carefully mapped. The choice of initially prepared Na states, 24d, 25s, 28d, 29s, 33d, and 34s, allowed a comparison of l=0 and ≥2 targets at nearly equal binding energies over a range of reduced velocity ṽ=0.187 to 1.95. Capture populates m sublevels broadly, not merely m≊0. Overlapping contributions from adiabatic and diabatic modes of field ionization were accommodated in the analysis, which used a maximum-entropy-principle parametric form to fit the observed final-state distributions. The peak of the distributions, ${\mathit{n}}_{\max }$, shifts upward from a value less than the initial state ${\mathit{n}}_{\mathit{i}}$ to a value one to three units higher than ${\mathit{n}}_{\mathit{i}}$ at ṽ between 0.7 and 0.9 and ultimately shifts downward below ${\mathit{n}}_{\mathit{i}}$ as ṽ is further increased. The distributions become significantly sharper where the maximum upward shift occurs. Two ratios were defined to express the widths of final-state distributions in relative terms, one measuring the spread of orbital kinetic energy and the other the spread of Bohr-orbit velocity. By these ratios a universal behavior over energies, states, and projectile species is observed, and small differences between l=0 and ≥2 targets may be seen. A theoretical understanding of the present results, which span velocities where both molecular and perturbative theories are normally used, will require a quantal formulation that models the free-ranging response that is a hallmark of the high-quantum-number limit.