Adsorption of small molecules with the hydroxyl group on sodium halide cluster ions

We have investigated adsorption of molecules with hydroxyl group, ROH, on sodium halide cluster ions, Na_nX_n-1(X = F and I, n = 10-17) by mass spectrometry and by theoretical calculations. From analysis of the cluster ion intensities, the adsorption of one water molecule (R = H) is most efficient for Na₁₃X₁₂⁺ whose structure has a NaX defect from a 3 × 3 × 3 cubic structure of n = 14. This result suggests that the defect has an important role in the adsorption reaction. However, it is also found that the reactivity diminishes with increasing bulk size of the R group from H to CH₃, (CH ₃)₂CH, and (CH₃)₃C. These results imply that the adsorption reactivity is dominated by steric hindrance; the smaller molecules are adsorbed inside the basket structures of Na ₁₃X₁₂⁺. Reactivity dependence on the basket size is also discussed by comparing the results of Na_nF _n-1⁺ and Na_nI_n-1⁺.