INNER-SHELL EXCITATION AND SITE-SPECIFIC FRAGMENTATION OF POLY(METHYLMETHACRYLATE) THIN-FILM

Soft x-ray excitations in the 250-600 eV photon energy range on poly(methylmethacrylate) (PMMA) result in ionic fragmentation of the original polymer with the most intense ions corresponding to CH3+, H+, CH2+, CH+, CHO+, and COOCH3+. The photon energy dependence of ion desorption from thin films of PMMA was measured to investigate the primary steps in radiation induced decomposition following carbon and oxygen 1s electron excitations using monochromatic pulsed-synchrotron radiation. It was clearly found that the decomposition depends on the nature of the electronic states created in the excited species. The fragmentation pattern changes depending on the transitions of the 1s electron to a Rydberg orbital, an unoccupied molecular orbital or the ionization continuum. Moreover, the fragmentation occurs specifically around the site of the atom where the optical excitation takes place. Excitations from carbon and oxygen 1 s to sigma* states seem to be specially efficient for ion production as observed in the case of CH3+, CH2+, and CH2+ at 288.7 and 535.6 eV, and in the case of CHO+ at 539.3 eV