Angular distributions for single- and double-electron capture in slow C4+-Ne collisions.

In an earlier experiment by H. Cederquist [ital et] [ital al]. [J. Phys. B 18, 3951 (1985)] an unusual [ital Q]-value distribution for true double-electron capture was reported for 400-eV C[sup 4+]-Ne collisions: a strong population of reaction channels resulting in [ital Q] values between 27 and 35 eV followed by weakly populated channels in the region 18--25 eV and then again a strong channel at [ital Q]=16 eV. The last channel is nearly degenerate in [ital Q] value with the dominant single-electron capture reaction. Here, we report measured angular distributions for scattered projectiles in single- and double-electron capture at collision energies 0.6--1.0 keV. At 0.6 keV, both single- and double-electron capture exhibit strong forward peaks for [ital Q][similar to]16 eV. The intensity for the latter, but not the former, decreases drastically when the energy is raised to 1 keV. The energy dependence of the angular distribution for double-electron capture with [ital Q][gt]20 eV can be qualitatively understood in simple terms; single-electron captures to 2[ital s] and 2[ital p] orbitals, however, yield unexpectedly wide and structured angular distributions.