MECHANISMS FOR THE DESORPTION OF LARGE ORGANIC-MOLECULES .2.

Models are reviewed for ejection of intact biomolecules and biomolecular ions in response to the electronic energy deposited by a fast heavy ion. These models are compared with laboratory data and molecular dynamics calculations. Over a limited range of electronic energy deposited per unit path length, the scaling of the total yield with energy deposition is understood, and it has been shown that, except for Langmuir-Blodgett films of fatty acids, the large intact ions are ejected primarily from the surface or adsorbed sites. The principal outstanding problems are a detailed description of the electronic energy conversion into molecular motion and the ion formation-neutralization process. An understanding of these is needed in order to improve sensitivity at the higher masses in PDMS.