X-ray Signature of Charge Exchange in L-shell Sulfur Ions

The X-ray signature of L-shell charge exchange in sulfur was studied in the laboratory. A comparison of the charge exchange (CX) spectra with those obtained under electron-impact excitation showed marked differences. In the CX spectra, an enhancement was observed in the transitions from levels with high principal quantum numbers, n = 4, 5, 6 → n = 2 in comparison with the n = 3 → n = 2 transitions that dominate the direct excitation spectra. An even greater enhancement was recorded in the transitions from the levels of electron capture to the ground states: n = 7, 8, 9 → n = 2. The spectra mainly consist of emission from S XIV, but lower charge states such as S XIII, S XII, and S XI also contribute. The results have been compared with observations made by the Chandra and XMM-Newton X-ray Observatories of Jupiter's polar regions. The enhancement we noticed in transitions from the high-n levels is not seen in the Chandra spectra.