Interference in dielectronic transitions in ${\mathrm{H}}_2^{+}+\mathrm{He}$ collisions

We study single ionization of helium by the impact of the ${\mathrm{H}}_2^{+}$ molecule which in the collision undergoes a transition from the ground state to its first dissociative state. We show that two types of interference effects arise in the spectra of the emitted electrons. One of them is due to the interaction of the atomic electron with the nuclei of the molecule. In the other one the interference is caused by the interaction of this electron with the electron of the molecule. Interference effects of the first type dominate at the low collision velocities due to the effective threshold for the electron-electron interactions.

Figure 1

The emission pattern calculated by neglecting the $ee$ mechanism. (a)–(d) correspond to collision energies of 500, 200, 100, and 50 keV/u, respectively. The molecular polar angle is $0^{\circ }$ and $\lambda =$ 4 a.u. In (b), (c), and (d) cross sections [Mb/(a.u.)${}^2]$ are multiplied by 0.17, 0.07, and 0.02, respectively.

Figure 2

Same as in Fig. 1 but neglecting the $eN$ mechanism. In (b), (c), and (d) cross sections [Mb/(a.u.)${}^2]$ are multiplied by 0.33, 0.22, and 0.35, respectively.

Figure 3

Electron emission spectrum calculated for three different molecular orientations: (a, b) ${\Theta }_M=0^{\circ }$, (c, d) ${10}^{\circ }$, and (e, f) ${20}^{\circ }$. The collision energy is 50 keV/u, and $\lambda =$ 4 a.u. The results shown in the left column were obtained by neglecting the $ee$ mechanism. In (b)–(f) cross sections [Mb/(a.u.)${}^2]$ are multiplied by 0.66, 1.19, 0.61, 1.61, and 0.55, respectively.

Figure 4

The energy spectrum of the electron emitted in the reaction (1). The orientation angle of the molecules randomly varies between $0{}^{\circ }$ and ${10}^{\circ }$ and $\lambda =4$ a.u. The dotted and dashed curves show the contributions of the $ee$ and $eN$ mechanisms, respectively. The solid curve is the full result.