Silica clusters were produced by laser vaporization of three different silica compounds and the ionized species were analysed by using Fourier transform ion cyclotron resonance mass spectrometry. Using a wavelength of 248 nm, negative-ion mass spectra of E2, Merck and Stöber's silica showed different ionized species. Such results may provide a point of departure for the ability of mass spectrometric techniques to distinguish silicas synthesized in different ways. From the data obtained and depending on the laser wavelength used (193, 248 and 355 nm), Stöber's silica was studied more precisely. In the negative-ion mode, three kinds of silica clusters were predominantly detected and their mass distribution was found to be dependent on the wavelength. These families of clusters are: SinO2n-, SinO2n+1- and SinO2n+1H-. Laser irradiation of silica at 355 nm illustrates a thermal approach to cluster formation. The irradiation of silica with a far-UV wavelength (193 or 248 nm) induced smaller clusters, owing to a more intense photoelectronic excitation contribution.
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Lafargue et al. (1996) studied this question.