LAUSR

We present reactions of size-selected free silicate, MglSiOm–, and silica, SinOm–, cluster anions with a H2O molecule focusing on H2O adsorption. It was found that H2O adsorption to MglSiOm– with l = 2 and 3 (m = 4–6) is always followed by molecular oxygen release, whereas reactivity of the clusters with l = 1 (m = 3–5) was found to be much lower. On the contrary, in the reaction of SinOm– (n = 3–8, 2n – 1 ≤ m ≤ 2n + 2), a H2O adduct is observed as a major reaction product. Larger and oxygen-rich clusters tend to exhibit higher reactivity; the rate constants of the adsorption reaction are 2 orders of magnitude larger than those of CO adsorption previously reported. DFT calculations revealed that H2O is dissociatively adsorbed on SinOm– to form two SiO3(OH) tetrahedra. The site selectivity of H2O adsorption is governed by the location of the singly occupied molecular orbital (SOMO) on SinOm–. The present findings give molecular-level insights into H2O adsorption on silica and silicate species in the inters...