We have experimentally studied the backward electron emission from solid carbon bombarded by ${\mathrm{H}}^{+}$, ${\mathrm{H}}^0$, ${\mathrm{H}}^{\mathrm{-}}$, and ${\mathrm{H}}_2^{+}$ projectiles at MeV energies. We used a coincidence ion-by-ion technique that allows us to obtain not only the average electron yields but also the emission statistics. The comparison of energy dependences of electron emission due to ${\mathrm{H}}^{+}$ and ${\mathrm{H}}^0$ projectiles helps to specify the role of the incident electron of ${\mathrm{H}}^0$. For ${\mathrm{H}}^{\mathrm{-}}$ and ${\mathrm{H}}_2^{+}$, the equality of electron yields above 500 keV/u supports the idea that backward emission is due to distant collisions.

• Received 30 July 1996

DOI:https://doi.org/10.1103/PhysRevA.55.1124