We report on the first (7-value measurements in charge-transfer collisions using recoil longitudinal momentum spectroscopy. This method is not limited to relatively low beam energies and is easily adaptable to captures involving any number of transferred electrons. A very monoenergetic beam is not necessary. For a 50-keV Ar ,5+ on Ar collision system, Q values corresponding to single through quintuple electron capture were measured and found to be in good agreement with the predictions of the molecular classical overbarrier model. PACS numbers: 34.70.+e, 34.50.Fa When a multiply charged ion moving at a velocity below that of typical outer shell atomic electrons encounters a neutral target, the dominant electron removal process is electron capture. The change in electronic energy, or Q value, for such a process is a direct measure of the distribution of final states populated on the projectile, which is in turn one of the most crucial tests of any theoretical description of the process. Direct measurement of the energy gain of the projectile has often been used to determine this final-state distribution [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]. Since the fractional energy resolution practically achievable rarely exceeds 10 ~3, this technique has usually been limited to projectiles of 10 keV and less, and to single and double capture. For higher energies, measurement of Q through direct energy change of the projectile becomes increasingly more difficult [17]. It has been pointed out previously that recoil ion longitudinal momentum can yield direct information on the Q value and electron mass transfer in fast-ion-atom collisions [18]. In this work we report the first experimental use of recoil longitudinal momentum spectroscopy to obtain Q values for capture. The technique is not limited to collision energies below a few keV, and can be used in situations for which the beam energy is not very well determined. This technique is readily applicable to any charge-transfer number, and is not affected by the kinematic broadening due to autoionization of the projectile following the collision. We apply the method to measure Q values for up to fiveelectron transfer for Ar 15 " 1 " ions on Ar.For collisions involving /-electron capture, conservation of both energy and momentum results in a simple relation between the Q value of the collision and the momentum transfer to the recoil given by (in a.u.)(1) where v is the projectile velocity, P\\ and P± are the longitudinal and transverse (relative to the beam direction) components of the momentum transfer to the recoil, and M\ and Mi are the projectile and recoil masses, respectively. The term iv 2 /2 appears due to the fact that the captured electrons are moving with the projectile at velocity r just after the collision. We will show later that Q' is much smaller than QQ and to a very good approximationsuch that it is sufficient to measure P\\ to obtain Q values. We wish to emphasize that this technique applies only to pure electron capture collisions, and bre...

The angular distributions of dissociated deuterons for electron capture and ionization by bare oxygen ions with energies from 2 to 16 MeV in collision with molecular deuterium targets were measured. The dependence of the differential cross sections on the alignment of the molecular axis with respect to the beam axis was determined. The results show that in the transfer ionization and transfer excitation processes, the deuterium molecules are more likely to be aligned perpendicular to the incident beam than parallel to the beam. This feature can be qualitatively interpreted as resulting from the interference of capture amplitudes from the two atomic centers. In the double ionization and ionization excitation processes, little alignment dependence was observed.PACS number(s): 34.70.+ e, 34.50.Gb

No abstract

No abstract