Dissociative 70-eV electron ionization of tetraethoxysilane (I) and triethoxysilane (11) affords silicon dihydroxide, Si(OH)(2)(+.) (1(+.)), and silanoic acid, HSi(O)OH+. (2(+.)) ions, respectively, While the collision 2 induced dissociation (CID) spectra of 1(+.) and 2(+.) confirmed their connectivities, isomerization processes from 1(+.) to 2(+.) and vice versa are not ruled out. Neutralization-reionization (NRMS) of these structurally characterized ions confirmed that the corresponding neutral molecules, silicon dihydroxide and silanoic acid are stable in the gas phase, The relative, dissociation, and transition state energies for the ions and neutrals studied at B3LYP/6-31G(d.p). B3LYP/6-311+G(2d.p) (DFT) and G2, G2-MP2 were used to support and interpret the experimental results. (C) 2002 Elsevier Science B.V. All rights reserved.