Rearrangement reaction in electron scattering from antiprotonic helium ions $\left(\overline{p}{\text{He}}^{2+}\right)$ in highly excited states, i.e., $e+\overline{p}{\text{He}}^{2+}\to \overline{p}+{\text{He}}^{+}$, is theoretically investigated by using the $R$-matrix method. This type of reaction can be identified as dissociative recombination (DR) which is well known in molecular physics. If the concept of the adiabatic Born-Oppenheimer separation is applied, the present exotic reaction has a similarity to the DR of ${\text{HeH}}^{+}$ molecules in the sense that the system has no crossings of the adiabatic potential curves. The present exotic DR reaction shows a variety of resonances, which can be described as a Rydberg electron attached to a $\overline{p}{\text{He}}^{2+}$ ion excited to an energetically forbidden state. The cross sections and rate coefficients for the present DR are calculated. As the bound motion of $\overline{p}{\text{-He}}^{2+}$ is closer to a circular orbit, the DR reaction, which leads to the destruction of $\overline{p}{\text{He}}^{2+}$, occurs less frequently. For the antiprotonic ion $\overline{p}{\text{He}}^{2+}$, it turns out that the circular states are the most stable against electron impacts.

• Received 15 March 2009

DOI:https://doi.org/10.1103/PhysRevA.79.042508