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 benzene, along with the corresponding photoabsorption spectra, have been measured with various polarization angles of incident synchrotron radiation (SR) in the C 1s region. Polarization analysis of photoabsorption measurement showed that molecular planes of the adsorbed benzene molecules were randomly oriented. However, enhanced ion yields were observed at some resonances corresponding to in-plane transition, i.e. s-symmetry, when the electric ®eld vector (E) of SR became close to parallel to the surface normal. The results 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 probabilities in grazing incidence angles of less than 108. This suggests that the contribution of a secondary effect resulting from bulk electrons is suppressed because the penetration depth of soft X-rays becomes small. # 2001 Elsevier Science B.V. All rights reserved