Figure 1

(a) Distribution of the KER after breakup into ${\mathrm{He}}^{+}/{\mathrm{He}}^{+}$ for DC and TI [Eq. (1, 2)]. The grey area indicates the region of decreased detection efficiency. Based on geometrical arguments, we have estimated that this reduces the measured cross section of the two-step process by a factor of 2. (b)–(d) Sketches of the sequence of events leading to the different peaks in (a); see text.Reuse & Permissions

Figure 2

Angular distribution of the fragmentation axis of the dimer with respect to the fast ion beam axis [(purple) arrow]. For $\cos \Theta <0$. the experimental and simulated data in (a) and (b) are shifted by ($+2.0$). (a) TI, $\mathrm{KER}=3.5–5.0\mathrm{eV}$. For $\mathrm{KER}<3.5\mathrm{eV}$ the detection efficiency is heavily decreased [see Fig. 1]. In case of full efficiency the small KERs (large internuclear distances) would lead to a even more accentuated angular distribution. The simulated distribution is the sum of two curves corresponding to the different pathways. (b) DC, $\mathrm{KER}=3.5–5.0\mathrm{eV}$. The small peak on the right side results from background events. (c) TI, $\mathrm{KER}=6–9\mathrm{eV}$ [peak 3 in Fig. 1]. The slight enhancement along the projectile direction originates from events of process 1 which can not be completely suppressed due to the small overlap between the KER regions. (d) $\mathrm{KER}=9–10\mathrm{eV}$ [peak 2 in Fig. 1]. The grey area in the polar plots and in the $\cos \Theta$ distribution indicate the angular regions of decreased detection efficiency. (e) (${\mathrm{He}}^{2+}\mathrm{He}$) potential energy curve.Reuse & Permissions

Figure 3

Calculated impact parameter dependence $P(b)$ which were used to generate the angular distributions shown in Figs. 2a, 2b. The distributions are obtained by an effective single-particle approximation [24]. To readily identify the width, the distributions were stretched. Since the $P(b)$ for the SI and SC of (${\mathrm{He}}^{+}+\mathrm{He}$) and ($p+\mathrm{He}$) hardly differ the $P(b)s$ of ($p+\mathrm{He}$) were used for the calculation. For TI F ($\cos \Theta$) was obtained by the $P(b)s$ of SC (${\mathrm{He}}^{2+}+\mathrm{He}$), SI ($p+\mathrm{He}$) and SI (${\mathrm{He}}^{2+}+\mathrm{He}$), SC (${\mathrm{He}}^{2+}+\mathrm{He}$). For DC F ($\cos \Theta$) was calculated by the $P(b)s$ of SC (${\mathrm{He}}^{2+}+\mathrm{He}$), SC ($p+\mathrm{He}$).Reuse & Permissions

Figure 4

Kinetic energy release (ions) versus kinetic energy of the continuum electron for TI. The diagonal feature is a characteristic of ICD (equation in the top). $n=2$, 3, 4 indicates the ICD electrons for excitation to the intermediate state [${\mathrm{He}}^{+}(n)$, He].Reuse & Permissions