The high reactivity of freshly cleaved metal oxide surfaces toward water shows itself through the strong chemisorption of water vapor at very low partial pressures (see Chapter 2). At low degrees of coverage, dissociative chemisorption takes place through the interaction with acidic and basic surface sites. The former are low-coordination metal ions and the latter low coordination oxide ions, 1 as shown schematically in Equation 9.1: https://www.w3.org/1998/Math/MathML"> | ≡ M − O ≡ M + H 2 O | ≡ M − OH ≡ M − OH https://s3-euw1-ap-pe-df-pch-content-public-u.s3.eu-west-1.amazonaws.com/9781351070515/0beef18d-6fba-4b0a-90e8-3e77c07379c2/content/eq9_1.tif" xmlns:xlink="https://www.w3.org/1999/xlink"/>