Fragmentation of the 4He2 dimer by relativistic highly charged projectiles in collisions with small kinetic energy release

We study theoretically the fragmentation of the helium dimer, 4He2, into singly charged ions in collisions with relativistic highly charged projectiles. We discuss the main mechanisms driving this process with the focus on the fragmentation caused by direct ionization of both atomic sites of the dimer in a single collision with the projectile. This direct mechanism dominates the He2 ??? He+ + He+ breakup events with the kinetic energies of the emerging ionic fragments below 4???5 eV. We explore the energy and angular distributions of the He+ ions produced in collisions with 1 and 7 GeV/u U92+ projectiles and show that their shape is significantly affected by relativistic and higher-order effects in the interaction between the projectile and the dimer. We also show that the shape of the energy spectrum is quite sensitive to the binding energy of the He2 dimer, which can be exploited for its precise determination. The contribution of the direct mechanism to the total cross section for the He2 fragmentation by 1 and 7 GeV/u U92+ was calculated to be 3.65 Mb and 2.4 Mb, respectively, representing roughly half of this cross section.

Automated summary

We theoretically study the fragmentation of the helium dimer, 4He2, in collisions with relativistic highly charged projectiles. Our focus is on the direct ionization mechanism that leads to the fragmentation of both atomic sites of the dimer in a single collision. We find that this mechanism dominates the breakup events with low kinetic energies and show that the shape of the energy spectrum is sensitive to the binding energy of the dimer.