Molecular-Ion Effects in Backscattering from Aligned Silicon Crystals

We have observed the proton spectra from equal-velocity beams of ${\mathrm{H}}^{+}$, ${\mathrm{H}}_2^{+}$, and ${\mathrm{H}}_3^{+}$ incident on aligned silicon crystals. Data for both axial and planar channeling show that the dechanneling is successively greater for the ${\mathrm{H}}_2^{+}$ and ${\mathrm{H}}_3^{+}$ ions than for protons. Since the depth at which dechanneling occured can be deduced from the energy spectrum of the backscattered protons, the comparison of the proton spectrum from molecular-ion bombardment with that produced by incident protons allows us to study the history of the motion in the crystal of the interacting protons from a given molecular ion.