Mutiple ionization of rare gases by electron impact

Electron impact studies of multiple io nization processes in helium, neon, a rgon , and xenon appear to support theoretical co nclusions that the threshold probability for n-fold ionizat ion is proportion a l to the nth power of the electron en ergy in excess of the threshold energy . The probability law a pplies, for the cases stud ied, over a considerable energy range that, for all but H e2+, includes the possible onset of more t han on e mode of ioni zation . The presence of a Boltzmann spread in the energy of the electron beam or specific fo cusing effccts due to ion source geometry are found to a ffcct only the foo t of the probability c urve. B y t he use of certain assumptions, an estimate is also m a de of t he depar t ure from a 3p ionization probability curve resulting from onset of ionization to the ID a nd 18 states.