Probing the Helium Dimer by Relativistic Highly Charged Projectiles

We study the fragmentation of ${\mathrm{He}}_2$ dimers into ${\mathrm{He}}^{+}$ ions by relativistic highly charged projectiles. We demonstrate that the interaction between an ultrafast projectile with an extremely extended object—the helium dimer—possesses interesting features that are absent in collisions with “normal” molecules. We also show that such projectiles, due to their enormous interaction range, can accurately probe the ground state of the dimer and even be used for a determination of its binding energy.

Figure 1

Cross section for producing two ${\mathrm{He}}^{+}$ ions by ${\mathrm{U}}^{92+}$ projectiles via the DF as a function of $R_{\perp }$. (Note that at $\gtrsim 5\mathrm{GeV}/\mathrm{u}$ all nonrelativistic results practically coincide.)

Figure 2

Same as in Fig. 1, but as a function of the impact energy.

Figure 3

The dimer ground state and the adiabatic radius $R_a$ at different impact energies.

Figure 4

The weighted probability $bP(b)$ for the DF given as a function of the impact parameter $b$.

Figure 5

(a) $d{\sigma }^{\mathrm{frag}}/d{E}_{\ker }$ for the fragmentation by $5\mathrm{GeV}/\mathrm{u}$ ${\mathrm{U}}^{92+}$ averaged over the dimer orientation angle ${\theta }_{\mathit{R}}$. (b) The ratio of the spectra obtained with $I_b=151.9$ and 139.2 neV. The ratio was normalized to 1 at $E_{\ker }=60\mathrm{meV}$ and turned out to be practically the same for both orientation ranges.