  The energy deposition and the atomic processes, such as the electron-capture,
ionization, excitation and radiative-decays for slow heavy ions in plasma
remains an unsolved fundamental problem. Here we investigate, both
experimentally and theoretically, the stopping of 100 keV=u helium ions in a
well-defined hydrogen plasma. Our precise measurements show a much higher
energy loss than the predictions of the semi-classical approaches with the
commonly used effective charge. By solving the Time Dependent Rate Equation
(TDRE) with all the main projectile states and for all relevant atomic
processes, our calculations are in remarkable agreement with the experimental
data. We also demonstrated that, acting as a bridge for electron-capture and
ionization, the projectile excited states and their radiative decays can
remarkably influence the equilibrium charge states and consequently lead to a
substantial increasing of the stopping of ions in plasma.
