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(n)X(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 Na(13)X(12)(+), whose structure has a NaX defect from a 3 x 3 x 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 CH(3), (CH(3))(2)CH, and (CH(3))(3)C. These results imply that the adsorption reactivity is dominated by steric hindrance; the smaller molecules are adsorbed inside the basket structures of Na(13)X(12)(+). Reactivity dependence on the basket size is also discussed by comparing the results of Na(n)F(n-1)(+) and Na(n)I(n-1)(+).