Orientation-selective excitation and dissociation in multilayer benzene

A newly constructed rotatable detector for desorption ion is described. The high resolution total yield spectra of desorbing ions from condensed benze ne, along with the corresponding photoabsorption spectra, have been measure d with various polarization angles of incident synchrotron radiation (SR) i n the C Is region. Polarization analysis of photoabsorption measurement sho wed that molecular planes of the adsorbed benzene molecules were randomly o riented. However, enhanced ion yields were observed at some resonances corr esponding to in-plane transition, i.e. sigma -symmetry, when the electric f ield vector (E) of SR became close to parallel to the surface normal. The r esults suggest that the probability of C-D dissociation and ion-desorption sequence becomes higher value in the molecular orientation perpendicular to the surface. The result also shows considerably high desorption probabilit ies in grazing incidence angles of less than 10 degrees. This suggests that the contribution of a secondary effect resulting from bulk electrons is su ppressed because the penetration depth of soft X-rays becomes small. (C) 20 01 Elsevier Science B.V. All rights reserved.