Gas-Phase Condensation Reactions of SixOyHz- Oxyanions with H2O

Abstract

Water was reacted with gas-phase oxyanions having the general composition SixOyHz- that were formed and isolated in an ion trap-secondary ion mass spectrometer (IT-SIMS). The radical SiO2•- reacted slowly with H2O to abstract HO•, forming SiO3H-, at a rate of 8 × 10-13 cm3 molecule-1 s-1, corresponding to an efficiency of about 0.03% compared with the theoretical collision rate constant (average dipole orientation). The product ion SiO3H- underwent a consecutive condensation reaction with H2O to form SiO4H3- at a rate that was approximately 0.4−0.7% efficient. SiO4H3- did not undergo further reaction with water. The multiple reaction pathways by which radical SiO3•- reacted with H2O were kinetically modeled using a stochastic approach. SiO3•- reacted with water by three parallel reaction pathways: (1) abstraction of a radical H• to form SiO3H-, which then reacted with a second H2O to form SiO4H3-; (2) abstraction of a radical OH• to form SiO4H-, which further reacted by consecutive H• abstractions to for...