SIOH+/HSIO+ AND SIOH./HSIO. - GAS-PHASE GENERATION AND CHARACTERIZATION - A COMBINED NEUTRALIZATION REIONIZATION MASS-SPECTROMETRY AND ABINITIO MOLECULAR-ORBITAL STUDY

Molecular orbital calculations (MP4(fc)6-311G(3df,3pd)//MP2(full)/6-311G(3df,3pd) + ZPE(MP2/full)/6-311G(3df,3pd)) are used to describe the geometries, energies, and vibrational frequencies of the fourspecies SiOH+ (1+), HSiO+ (2+), SiOH. (1.), and HSiO. (2.), respectively, and the transition states for the 1,2-hydrogen migrations. In line with previous theoretical findings, all four species reside in potential minima. The most stable form invariably corresponds to the SiOH+/. connectivity. Substantial barriers (35.3 kcal/mol for the cation and 29.5 kcal/mol for the radical) prevent facile isomerization. In line with the theoretical predictions, a combination of several mass spectrometric experiments (collisional activation and neutralization-reionization) provides evidence that all four species, which are believed to play a role in ionospheric chemistry, do indeed exist in the gas phase.