Photon stimulated ion desorption of polymer thin films following core excitation

We have studied the photon stimulated ion desorption of poly-isopropenyl-ac etate (PiPAc) and poly-vinyl-acetate (PVAc) thin films from the viewpoint o f site-specific bond scission. PiPAc is the structural isomer of PMMA, whic h shows site-specific bond scission. The structures of PiPAc and PVAc are d ifferent in the substitutional group of the side-chain, a methyl group or h ydrogen. H+, CH+, CH2+, CH3+ and COCH3+ are mainly desorbed from PiPAc and PVAc thin films following the oxygen core excitation. The near edge X-ray a bsorption fine structure (NEXAFS) spectra of these thin films are assigned through a comparison to the inner shell electron energy loss spectra of the related molecules. The features of the partial ion yield (Y-Pi) spectra of CH3+ and COCH3+ ions are different from that of the total electron yield ( Y-e) spectrum. This indicates that the efficiencies of desorption of these ions depend on the primary excitation and these ions are consequently desor bed site-specifically. The most remarkable difference in the Y-Pi is Seen i n the Y-Pi(CH3+) and Y-Pi(COCH3+) spectra. In Y-Pi(CH3+) and Y-Pi(COCH3+) s pectra, the peak is assigned to the O 1s(C=O) --> sigma*(C-C) with the help of this result.