Cluster size dependence of the H/D exchange reaction rate constant for protonated water clusters H+ (H2O)(n) (n=2-11)

摘要

The collisions of size- and energy-selected H+(H2O)(n) (n = 2-11) with D2O have been investigated using guided-ion beam mass spectrometry. The H/D exchange reaction was observed by incorporation of D2O into H+ (H2O)(n). The measured rate constants of this reaction are found to depend strongly on the cluster size- the rate constants drastically decrease up to n = 6, and then level off for 6 less than or equal to n less than or equal to 11. This size dependence is discussed in terms of the structure of protonated water clusters: the core H3O and H5O2+ ions, so-called Eigen and Zundel cations respectively, are completely surrounded by the first water layer and cause the rate constants for 6 less than or equal to n less than or equal to 11 essentially insensitive to n. (C) 2002 Elsevier Science B.V. All rights reserved. [References: 26]