THE DISSOCIATION OF LARGE ORGANIC IONS BY GRAZING INTERACTION WITH A SURFACE-POTENTIAL

The special excitation process observed in surface scattering experime nts with large organic molecules must be different from the ion-surfac e interactions related to classical surface induced dissociation. Exci tation by deformation, charge exchange and phonon generation are not l ikely to play a significant role, when a large molecular ion is surfin g for a short period of time on a wavy surface potential. Instead two other interaction processes are suspected to be responsible for the en ergy transfer into the sliding molecule: (i) Braking forces (friction) will cause the molecule to rotate and vibrate internally. If the resu lting centrifugal forces exceed a certain limit, the molecule can diss ociate. (ii) The peripheral dipoles of the molecule experience a perio dical surface potential with frequencies depending on molecule velocit y and surface lattice parameters. If those frequencies coincide with f requencies corresponding to the first vibrational excited state of the dipoles, resonance excitation can occur. The vibrational excitations have lifetimes which depend on the structure of the scattered molecule . In special cases they can be accumulated in the molecule during the interaction period until rapid dissociation of an internal bond is ind uced. In order to reveal the relation between molecular structure and the excitation process, the fragmentation of cyclodextrines and specia l derivatives thereof induced by grazing surface collisions is investi gated in a TOF-mass spectrometer for different surfaces.