Charge changing cross sections for heavy ions in complex molecules: the failure of an 'additive' rule

Electron capture and loss cross sections have been measured for 12 MeV iodine ions passing through H 2 , N 2 , O 2 , CO 2 , N 2 O, CH 4 and (CH 2 ) 3 O. It is shown that, in contrast to recent data for fast hydrogen beams, it is not possible in this case to predict the cross sections in a complex molecular target by summing contributions from the measured cross sections of its constituent atoms.