MULTICOINCIDENCE MASS-SPECTROMETRY APPLIED TO HEXAMETHYLDISILANE EXCITED AROUND THE SI 2P EDGE

Photoelectron-photoion-photoion coincidence (PEPIPICO) mass spectromet ry is applied to Si 2p core ionization. The ion yield spectrum is comp ared to the spectrum of the tetramethylsilane molecule in order to poi nt out resonances due to the Si-Si chemical bond. Simple coincidence m ass spectra are dominated by the SiC3H9+ fragment ion and do not show a strong dependence on photon wavelength. PEPIPICO spectra demonstrate that dissociation dynamics is dominated by stepwise fragmentation of SiC3H9+ and that double ionization always involves Si-Si chemical bond rupture, shown to be faster than the Si-C rupture. We discuss the res ults in term of a fast decay of Si-Si into singly and doubly charged m olecules followed by a cascade of slow fragmentation and isomerization Of SiC3H9+.