Role of excited electronic states in the interactions of fast (MeV) molecular ions with solids and gases

The authors report measurements of the joint distributions in energy and angle for fragments arising from the dissociation of 1.2-MeV ${\mathrm{H}}_2^{+}$ and 3.0-MeV He${\mathrm{H}}^{+}$ in thin carbon foils and in a variety of gases at several pressures. From the foil measurements the distribution of initial internuclear separations in the incident projectiles is derived. These distributions are then used in conjunction with the results for gas targets to determine the role of excited electronic states of the projectile in collisionally induced dissociation. Finally, it is shown how these states also play a vital role in some other phenomena that occur in the interactions of fast molecular ions with foils.