Angular distributions of selected N2 Auger transitions.

The angular distribution of Auger electrons produced in the collision of 1634-eV electrons with ${\mathrm{N}}_{2}$ is reported. The angular distributions are measured relative to the internuclear axis of the molecule from 0\ifmmode^\circ\else\textdegree\fi{} to 90\ifmmode^\circ\else\textdegree\fi{} in 6\ifmmode^\circ\else\textdegree\fi{} steps. When an Auger transition occurs to an unstable doubly ionized state the molecular ion dissociates into two ${\mathrm{N}}^{+}$ fragments. Because the time required for dissociation of the ${\mathrm{N}}_{2}^{2+}$ ion is much less than that for rotation of the ion, the axial recoil approximation holds to first order, and detecting one of the ${\mathrm{N}}^{+}$ ions determines the orientation of the target molecule at the time of the projectile-molecule collision. Therefore, a coincidence experiment between the Auger electrons of appropriate energy and the ${\mathrm{N}}^{+}$ fragments is devised. The rotation of the ${\mathrm{N}}_{2}^{2+}$ ions during the course of the dissociation process has been taken into account as a second-order approximation. As a result of this rotational effect, the predicted angular distribution function is smeared out by an amount depending on the different ${\mathrm{N}}_{2}^{2+}$ final states. The data are analyzed in terms of a two-center model in which prolate spheroidal coordinates are used.