We have determined the magnetic-substate alignment produced in double-electron capture by the H-like projectiles ${\mathrm{C}}^{5+}$ and ${\mathrm{B}}^{4+}$ from He atoms by measuring the anisotropy of the Auger electron emission from the doubly excited 1s2l2l’ ${}_{}{}^2{}_{}{}^{}$L projectile states formed in the collision. This work includes additional measurements and expands upon our previous short communication on the (${\mathrm{C}}^{5+}$,He) system [Phys. Rev. A 43, 607 (1991)]. The measurements yield ${\mathit{M}}_{\mathit{L}}$ substate population fractions which challenge theory at nearly the finest quantum state detail. We observe large differences between the results for ${\mathrm{B}}^{4+}$ and ${\mathrm{C}}^{5+}$ over the velocity range 0.25–0.50 a.u. for the substate and total 1s2l2l’ ${}_{}{}^2{}_{}{}^{}$L relative cross sections. Substantial population of ${\mathit{M}}_{\mathit{L}}$>0 states shows the importance of rotational coupling in these slow collisions. The large anisotropies observed demonstrate that substantial errors can result from inferring ‘‘cross sections’’ from single-angle measurements and the assumption of isotropic electron emission.

• Received 29 April 1993

DOI:https://doi.org/10.1103/PhysRevA.48.1964