Collision spectroscopy of Ar^{8+} + He at low velocities (v<1 a.u.)

Single- (SC) and double-electron capture (DC) have been studied for collisions of Ar8+ with He using x-ray and vacuum ultraviolet (vuv) spectroscopy at a collision energy of 80 keV as well as translational-energy spectroscopy (TES) at lower collision energies (8 keV). It is shown that both processes involving the ground-state ion terminate in vuv photon emission, i.e., nonautoionizing levels are populated. The SC, by the long-lived metastable species Ar8+* (2p(5)3s)P-3(0,2), populates mostly the Na-like core-excited levels with n = 4: Ar7+* (2p(5)3S P-3 41)2,4L(j). With the use of calculated decay and autoionization rates, the measured vuv spectra are analyzed and compared with the TES results and the Auger spectra measured by other authors. It is shown that the stabilization of these core-excited states is both radiative and autoionizing. The DC by the metastable projectile is not yet fully understood.