Gas-phase Si and Al oxyanions were formed by particle bombardment, isolated by mass, and then reacted with H2S in an ion trap secondary ion mass spectrometer (IT-SIMS). The reactions proceeded by different reaction pathways depending on whether the oxyanions were even- or odd-electron species. The radical anion SiO2bullet- reacted with H2S by abstracting a(bullet)SH radical to form the even-electron Sio(2)SH(-). Once formed, the even electron Sio(2)SH(-) reacted with a second H2S molecule by O-for-S exchange to form SiOS2H-. The radical anion SiO3bullet- abstracted an H-bullet radical from H2S to form even-electron SiO3H-, which then underwent two consecutive O-for-S exchange reactions with H2S to form SiO2SH- and SiOS2H-. For the reactions of the even-electron anion AlO2-, the products of two consecutive O-for-S exchange reactions with H2S were AlOS- and AlS2-. The radical abstraction reactions and the O-for-S exchange reactions of SiO3H-, AlO2 and AlOS- were efficient in the 30-50% range. The efficiency of the O-for-S exchange reaction of SiO2SH- (producing SiOS2H-) was substantially less efficient at 8%.