Collisional activation of large ions. Energy losses and an impulsive collision theory of energy transfer

Abstract

The translational energy losses, ΔE, experienced by keV beams of singly charged ions of high masses (> 1000u) in collisions with either an inert-gas atom or hydrogen molecule depend on the mass of the target gas employed. There is no evidence of a dependence on the ionisation energy of the target gas. ΔEs are similar with He and D₂ targets, and both are larger than those with Ar. This behaviour is found with organic ions composed of light atoms and with inorganic cluster ions composed of heavy atoms. The measured ΔEs are consistent with internal energy uptake, Q, occurring via direct momentum transfer in an impulsive collision. It is concluded that the Q taken up by an ion is dependent upon the masses of its constituent atoms. In collision with He, a light-atom ion of a given molecular mass takes up more Q than does a heavy-atom ion of similar molecular mass under the same experimental conditions, but the ΔE can be similar in the two cases.