Directional correlation between the primary particle and ejected molecular ions in electronic sputtering of large organic molecules

Fission fragments from a ${}_{}{}^{252}{}_{}{}^{}\mathrm{Cf}$ source and 72-MeV ${}_{}{}^{127}{}_{}{}^{}\mathrm{I}$ ions from an EN-tandem accelerator have been used to sputter secondary ions electronically from samples of biomolecules such as bovine insulin (5733 u). It is found that intact molecular ions of insulin are ejected from the surface at an angle which correlates with the incident ion direction. This study shows that from the ionized cylindrical region produced by the passage of a fast ion there is a direct radial momentum transfer, i.e., a nondiffusive process, which ejects large molecular ions.