SPECTROSCOPIC STUDY OF LOW-VELOCITY CHARGE-EXCHANGE COLLISIONS OF S7+ IONS WITH H2 AND HE TARGETS

The far-uv spectra of sodiumlike S VI and neonlike S VII are obtained following single- and double-electron capture into excited states of slow (approximately 10-keV/q) S7+ ions passing through thin H-2 and He gas targets. The high charge-state and excited-state selectivity of the collision process facilitated line identification. New model-potential calculations using the SUPERSTRUCTURE code are compared with measurements for S VII. Changes in relative line intensities observed using the different target gases help to elucidate the collision mechanism via the relative initial-state populations. Capture takes place into n states as predicted by a classical model, while the distribution among l states is nonstatistical at this velocity (approximately 0.29 a.u.).