Orientation Effects in Multiple Ionization of Molecules by Fast Ions

The multiple ionization and dissociation of N₂ molecules by fast He⁺ ions was studied by the coincident measurement of correlated fragment-ion momenta using a position- and time-sensitive multiparticle detector. The dependence of the cross section on the alignment of the molecular axis with respect to the beam axis was determined. The results show that for higher degrees of ionization the cross section has a pronounced minimum for molecules oriented perpendicular to the beam. The quantitative interpretation of the observed results is based on an extended version of the statistical energy deposition model.