LASER-ABLATION OF SILICA - STUDY OF INDUCED CLUSTERS BY FOURIER-TRANSFORM ION-CYCLOTRON RESONANCE MASS-SPECTROMETRY

Silica clusters were produced by laser vaporization of three different silica compounds and the ionized species were analysed by using Fouri er transform ion cyclotron resonance mass spectrometry. Using a wavele ngth of 248 nm, negative-ion mass spectra of E2, Merck and Stober's si lica showed different ionized species. Such results may provide a poin t of departure for the ability of mass spectrometric techniques to dis tinguish silicas synthesized in different ways. From the data obtained and depending on the laser wavelength used (193, 248 and 355 nm), Sto ber's silica was studied more precisely. In the negative-ion mode, thr ee kinds of silica clusters were predominantly detected and their mass distribution was found to be dependent on the wavelength. These famil ies of clusters are: SinO2n-, SinO2n+1- and SinO2n+1H-. Laser irradiat ion of silica at 355 nm illustrates a thermal approach to cluster form ation. The irradiation of silica with a far-UV wavelength (193 or 248 nm) induced smaller clusters, owing to a more intense photoelectronic excitation contribution.