DISSOCIATION CROSS-SECTIONS OF IONIC HYDROGEN CLUSTERS BY COLLISIONS WITH HELIUM AT 60 KEV AMU/

The dissociation of fast ionic hydrogen clusters H-n(+) by collision w ith helium atoms has been studied for various incident cluster masses (n=5,7,...,31) at 60 keV/amu energy. Absolute dissociation cross secti ons have been measured. No shell effect is observed. As expected, the cluster dissociation cross section increases with n but exhibits a qua silinear dependence in contrast with the n(2/3) dependence previously observed [M. Chevallier et al., Z. Phys. D 2, 87 (1986)] with argon at oms in the same velocity range.