De-excitation X-rays from resonant coherently excited 390 MeV/u hydrogen-like Ar ions

Resonant coherent excitation (RCE) of 390 MeV/u hydrogen-like Ar17+ ions pl anar channeled in a Si crystal was investigated through measurements of the de-excitation X-rays as well as the charge state distribution of the trans mitted ions. We observed enhancements of both the fraction of ionized Ar18 ions and the intensity of the de-excitation X-rays under the RCE condition . The n = 2 states of Ar17+ in the crystal are split into four energy level s due to spin-orbit interaction and Stark effect induced by the planar pote ntial of the crystal. The intensities of the X-rays from the lower two leve ls were found to be smaller compared with those from the higher two levels, which is explained by the dominance of the 2s component not decaying via a single photon emission. The difference between the resonance profiles of t he charge state and the X-ray reflects the nature of n = 2 states in the cr ystal field. (C) 2000 Elsevier Science B.V. All rights reserved.