Super fast selective fragmentation of organic molecules induced by IR radiation



Super fast selective fragmentation of organic
molecules induced by IR radiation

H. Jungclas1, L. Schmidt1, V. V. Komarov2, A. M. Popova2, I. O. Stureiko2

1Department of Chemistry, Philipps-University Marburg, 35032 Marburg, Germany;
2Institute of Nuclear Physics, Lomonosov State University, 119899 Moscow, Russia

Received: 15.10.2004; revised: 09.05.2005

A theoretical approach to the dissociation of organic molecules by radiation in the mid-IR spectrum (λ ~ 5–25 μm) is presented. It is assumed that the molecules contain antennas i. e. substructures of identical periodically located diatomic dipoles.  In these antennas collective vibration excitations (excimols) are resonantly and coherently produced and accumulated by  suitable resonant IR radiation. The energy of an excimol is lower than the energy of the first vibration state of an isolated  antenna dipole. The accumulated excimols can practically simultaneously transit inside the molecule to a near bond (trap  bond), which is also forming a dipole but does not belong to the antenna. The trap bond is cleaved if the accumulated excimol energy is equal to its dissociation energy. This process completes within a time period less or equal to the excimol lifetime  and thus can be referred to as a super fast dissociation compared to typical time scales calculated by statistical dissociation  models. The excimol model presented here predicts that the probability of the considered dissociation process resonantly  depends on the frequency and intensity of IR radiation. The present theoretical model was examined by experimental studies of the fragmentation of specific organic molecules were grazing along different surfaces at velocities 10 3 -10 4  m / s. The  effect of grazing incidence surface induced dissociation (GI-SID) was clearly shown. By using GI-SID experiments, the role  of molecular antennas was established. It was also experimentally shown, that the fragmentation probability depends on  locations and orientations trap-bonds relative to dipoles in the molecular antennas.