Vacancy-Transfer Cross Sectiqns and L-Vacancy Lifetimes for Low-Energy Collisions of Ar++ with Mg, Al, and Si

Electron promotion via rotational coupling of the 2p¿-2p¿ molecular orbitals in the quasimolecule formed during a near-symmetric collision between a heavy ion and a lighter target atom has successfully explained the K x-ray emission from the target atom. For atoms in a solid target, the target density fosters a double-collision mechanism whereby a fraction of the ion beam brings an L-shell vacancy into a subsequent collision with a target atom so that K-electron transfer from the target to the projectile can occur. On this basis we have performed a thick-target K-shell ionization analysis on target x-ray yields for 160-380 keV Ar++ impinging on Mg, Al, and Si. Our measurements yield the equilibrium L-vacancy fraction and the L-vacancy lifetime for the Ar++ beam moving through these targets.