| Vol. 53,
No. 4 October 1999 pp. 743-764 Multiple ionization of argon in coincidence with projectile ions in 60-120 MeV Siq+ -Ar collisions M J SINGHy, D O KATARIA* N MADHAVAN* , P SUGATHAN* , J J DAS* ,D K AWASTHI* ,A K SINHA* and R SHANKER Atomic Physics Laboratory,
Department of Physics, Banaras Hindu University, Varanasi
221 005, India Abstract. A projectile ion-recoil ion coincidence technique has been employed to study the mul-tiple ionization and the charge transfer processes in collisions of 60-120 MeV Si q+(q = 4 -14 ) ions with neutral argon atoms. The relative contribution of different ionization channels, namely; direct ionization, electron capture and electron loss leading to the production of slow moving mul-tiply charged argon recoil ions have been investigated. The data reported on the present collision system result from a direct measurement in the considered impact energy for the first time.The total ionization cross-sections for the recoil ions are shown to scale as q1:7/Ep0:5 ,where Ep is the energy in MeV of the projectile and q its charge state.The recoil fractions for the cases of total- and direct ionizations are found to decrease with increasing recoil charge state j. The total ionization fractions of the recoils are seen to depend on q and to show the presence of a 'shell-effect' of the target. Further, the fractions are found to vary as 1 / j 2 upto j = 8+ . The average recoil charge state <j> increases slowly with q and with the number of lost or captured electrons from or into the projectile respectively. The projectile charge changing cross-sections s qq' are found to decrease with increasing q for loss I ionization and to increase with q for direct- and capture ionization processes respectively. The physics behind various scaling rules that are found to follow our data for different ionization processes is reviewed and discussed. Keywords. Multiple ionization; recoil ions; charge state fractions; scaling rules. |