Experimental and Computational Study of Hydration Reactions of Aluminum Oxide Anion Clusters

Abstract

Hydration of aluminum oxide anion clusters was studied in the gas phase using an ion trap secondary ion mass spectrometer. Hydration of both AlO2- and Al2O4H- occurred by the consecutive addition of two H2O molecules. For hydration of AlO2-, the rate constants for addition of the first and second water molecules are 4 × 10-11 and 4 × 10-10 cm3 molecule-1 s-1, respectively. The first and second hydration rate constants for Al2O4H- are 2 × 10-9 and 8 × 10-10 cm3 molecule-1 s-1, respectively. A comparison of the experimental rate constants to the theoretical rate constants reveals that addition of the first H2O to AlO2- is only 2% efficient, whereas addition of the first H2O to Al2O4H- is 100% efficient. Ab initio calculations were performed to assist in the interpretation of the kinetic results. Reaction mechanisms and energetics for the hydration of the AlO2- system were calculated using the HF/6-311+G(d(Al),p), B3LYP/6-31+G(d), B3LYP/6-311+G(2d,p), B3LYP/6-311+G(3d2f,2p), and MP2/6-311+G(2d,p) levels of t...