Ionic desorption in valence- and core- excited polymers: poly(vinyl chloride) and poly(vinylidene chloride)

Abstract

Photon stimulated ion desorption (PSID) studies have been performed in poly(vinyl chloride) (PVC) and poly(vinylidene chloride) (PVDC) using synchrotron radiation, covering from valence to core electron (Cl 2p and C 1s) energy ranges. Data acquisition was performed at the TGM beam line from the Brazilian Synchrotron Light Source (LNLS), operating in a multi-bunch mode and using a time-of-flight mass spectrometer (TOF-MS). A new pulsed system developed uses as a trigger for the TOF-MS experiments the pulsed extraction high voltage applied to the sample. Ionic desorption from PVC and PVDC shows strong selectivity in the formation of chlorine ions around the Cl 2p-edge while very similar fragmentation patterns are observed for the other energies studied.

Site-selective photofragmentation of chlorinated polymeric films observed around the chlorine K-edge

“…In particular, our previous photon stimulated ion desorption (PSID) studies performed on PVC and PVDC films with photon energies covering the valence, Cl 2p and C 1s energy ranges showed element-selectivity as evidenced by an increase in the chlorine ion yield around the Cl 2p-edge as compared to the other excitation energies. This feature was associated to a resonant Auger process along the Cl 2p-edge [9,10]. Similar ion desorption results were obtained for PVDC [10].…”

“…This feature was associated to a resonant Auger process along the Cl 2p-edge [9,10]. Similar ion desorption results were obtained for PVDC [10]. Positive and negative electron stimulated ion desorption (ESID) performed on PVC films as a function of the electron energy indicated that at higher electron energies, inner-shell ionization processes followed by Auger decay play an important role in the positive ion desorption of chlorine species.…”

“…Ion desorption generated by photoexcitation at shallow and deep core levels has already proved to be an attractive topic in surface science since it is a surface phenomena that allows to investigate composition, electronic structure and site-selective fragmentation. Mainly interested in fundamental aspects, our group has performed several previous studies using small chlorinated molecules [5] or polymers, such as poly(vinyl chloride) (PVC) and poly(vinyl dichloride) (PVDC) [6][7][8][9][10], using electrons or high energy photons as excitation sources. In particular, our previous photon stimulated ion desorption (PSID) studies performed on PVC and PVDC films with photon energies covering the valence, Cl 2p and C 1s energy ranges showed element-selectivity as evidenced by an increase in the chlorine ion yield around the Cl 2p-edge as compared to the other excitation energies.…”

“…In the present study, NEXAFS (Near-edge X-ray absorption fine structure) and PSID spectra were acquired at the chlorine 1s-edge for PVC and PVDC, two chlorinated polymers containing a different number of chlorine atoms, in order to gain insight into the photofragmentation process induced by a deep core level, by comparing the contributions from direct (Auger) and indirect (secondary electrons) mechanisms to ionic desorption. Also the purpose of the work is to complement fragmentation studies performed previously on these films covering other energy intervals, ranging from valence to shallow inner-shell excitations [6][7][8][9][10]. The Cl 1s-edge was selected in order to evaluate possible improvements in the site-selectivity fragmentation of the C-Cl bond caused by chlorine core-shell excitation, since it is expected that excitation of localized electrons may favor selective bond breaking.…”