MOMENTUM SPECTRA FOR SINGLE AND DOUBLE-ELECTRON IONIZATION OF HE IN RELATIVISTIC COLLISIONS

The complete momentum spectra for single and double ionization of He b y 1-GeV/u (beta=0.88) U92+ have been investigated using a classical tr ajectory Monte Carlo method corrected for the relativistic projectile. The 1/r(12) electron-electron interaction has been included in the po st-collision region for double ionization to incorporate the effects o f both the nuclear-electron and electron-electron ionizing interaction s, and to access the effects of electron correlation in the electron s pectra. Experimental measurements were able to determine the longitudi nal momentum spectra for single ionization; these observations are in accordance with the theoretical predictions for the three-body momentu m balance between projectile, recoil ion, and ionized electron. In par ticular. the Lorentz contraction of the Coulomb interaction of the pro jectile manifests itself in the decrease of the post-collision interac tion of the projectile with the electron and recoil ion, causing them to recoil back-to-back as in the case for a short electromagnetic puls e. This feature is clearly displayed in both the theoretical and exper imental longitudinal momentum spectra, and by comparing to calculation s that are performed at the same collision speed but do not include th e relativistic potentials. Moreover, collision plane spectra of the th ree particles demonstrate that the momenta of the recoil ion and ioniz ed electron are preferentially equal, and opposite, to each other. The electron spectra for double ionization show that the inclusion of the electron-electron interaction in the post-collision regime partitions the combined ionization momentum of the electrons so that the electro ns are preferentially emitted in opposite azimuthal angles to one anot her. This is in contrast to calculations made assuming independent ele ctrons. [S1050-2947(97)08411-4].