We present experiments demonstrating trajectory-dependent electronic excitations at low ion velocities, for which ions are expected to primarily interact with delocalized valence electrons. The energy loss of ${\mathrm{H}}^{+},$ ${{\mathrm{H}}_2}^{+},$ ${\mathrm{He}}^{+},$ ${\mathrm{B}}^{+},$ ${\mathrm{N}}^{+},$ ${\mathrm{Ne}}^{+},$ ${}^{28,29}\mathrm{Si}^{+},$ and ${\mathrm{Ar}}^{+}$ in self-supporting silicon membranes was analyzed along channeled and random trajectories in a transmission approach. For all ions, we observe a difference in electronic stopping dependent on crystal orientation. For heavier ions, the energy-loss difference between channeling and random geometry is generally found more pronounced, and, in contrast to protons, increases for decreasing ion energy. Due to the inefficiency of core-electron excitations at employed ion velocities, we explain these results by reionization events occurring in close collisions of ions with target atoms, which are heavily suppressed for channeled trajectories. These processes result in trajectory-dependent mean charge states, which strongly affect the energy loss. The strength of the effect seems to exhibit a $Z_1$ oscillation with an observed minimum for Ne. We, furthermore, demonstrate that the simplicity of our experimental geometry leads to results that can serve as excellent benchmark systems for dynamic calculations of the electronic systems of solids using time-dependent density functional theory.

中文翻译：

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玻尔速度上下的轻离子和重离子对轨道的电子激发

我们目前的实验展示了在低离子速度下轨迹依赖的电子激发，对于这些离子，离子预期主要与离域价电子相互作用。的能量损失${\mathrm{H}}^{+}，$ ${{\mathrm{H}}_2}^{+}，$ ${他}^{+}，$ ${\mathrm{乙}}^{+}，$ ${\mathrm{ñ}}^{+}，$ ${\mathrm{NE}}^{+}，$ ${}^{28，29}硅^{+}，$ 和 ${\mathrm{氩气}}^{+}$在自支撑硅膜中，沿传输路径沿着通道和随机轨迹进行分析。对于所有离子，我们观察到电子停止的差异取决于晶体的取向。对于较重的离子，通常会发现沟道效应和随机几何形状之间的能量损失差更加明显，并且与质子相反，离子损失的能量损失增加。由于在所采用的离子速度下核电子激发效率低下，我们通过在离子与目标原子的紧密碰撞中发生的重离子化事件来解释这些结果，这对于通道化轨迹是受到严重抑制的。这些过程导致轨迹相关的平均电荷状态，这会严重影响能量损失。效果的强度似乎表现出${ž}_{\mathrm{1个}}$振荡，观察到的最小值为Ne。此外，我们证明了我们实验几何的简单性导致的结果可以用作出色的基准系统，该系统可以使用时变密度泛函理论对固体电子系统进行动态计算。