Angular correlation of the N+ ions produced in the dissociative double ionization of nitrogen

The double ionization of N2 by He+ projectiles was studied by measuring the angular correlation between the two N+ ions emitted in the dissociation of N2+2 molecular ions. If there were no recoil velocity imposed on the N2+2 ion in the initial ionizing collision, and thermal effects were neglected, the pair of N+ ions would have equal and opposite velocity vectors in the laboratory frame of reference. Measuring the coincidence yield of pairs of N+ ions as a function of the angle between their velocity vectors permits an estimate to be made of the component of momentum transferred to the N2+2 parent ions in the beam direction. The results presented in this report show the recoil velocity to be considerably less than the mean thermal velocity of N2 molecules at room temperature. We also report mesurements of the relative cross section for N+ production from N2+2 as a function of the orientation of the N2 target molecules relative to the projectile beam axis.