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
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