Study of inner shell excitation effect on C-H dissociation in aromatic hydrocarbon solids

Since Carson et al. have reported the 'Coulomb Explosion' model, an inner shell excitation effect on dissociation is intensively attractive because multiply ionized states induced by Auger decay enhance dissociation. This effect on chemical reaction has been investigated especially for surface reaction processes such as desorption induced electron transition (DIET). Recently, some studies on DIET using monochromatic soft X-rays have reported that desorption yield depends on not only the repulsion energy but also the character of excited molecular orbital (MO). This means that inner shell resonant excitations to different MO result in different desorption. This Inner Shell Resonant Excitation Effect' is very interesting because it enables us to control photochemical reactions with synchrotron radiation. Two important problems lie ahead of us for application of this effect. One problem is secondary effect. When one irradiates soft X-rays to materials, following reaction includes two kinds of mixed effects; fundamental effect (FE) and secondary effect (SE). FE originates from interactions between photons and materials, while SE originates from interactions between secondary electrons and materials. Since the inner shell resonant excitation effect essentially originates from FE, it is important to know the ratio of FE to SE in a photochemical reaction in order to estimate true magnitude of the inner shell resonant excitation effect. The other problem is the difference between surface reaction and bulk reaction. Weather the bulk reaction shows inner shell excitation effect as well as the surface reaction does? Some studies of the inner shell excitation effect on damage in bulk have been reported. To our knowledge, however, there is no study which reports the difference between bulk and surface reaction. In this paper, we present two kinds of works with aromatic hydrocarbon compounds. First, we present photon stimulated ion desorption (PSID) on condensed benzene to study the inner shell excitation effect on surface. Secondly, we present color center formation in anthracene single crystals to study that on bulk. (author)