Probing several structures of Fe(H2O)n+ and Co(H2O)n+ (n=1,...,10) cluster ions

Co(H2O)(nless than or equal to10)(+) and Fe(H2O)(nless than or equal to10)(+) cluster ions were generated in a source combining laser ablation and a supersonic expansion. The clusters were fragmented to get insight into their structure. Two questions were addressed: first, the arrangement of the water molecules about the metal ion, and second, the electronic properties of the solvated metal ion. Collision induced dissociation by helium was used to answer the first question, especially for the smallest clusters with n = 2 and 3. This revealed the existence of filament structures where one water molecule lies in the second solvation shell about the metal ion although the first shell is not filled. The binding energies of second shell water in Co(H2O)(2)(+) and Fe(H2O2)(2)(+) are 0.45 +/- 0.1 and 0.5 +/- 0.1 eV, respectively. The answer to the second question was provided by photofragmentation experiments where the cluster ions are illuminated at 532, 355 and 266 nm. The most striking effect is seen with cobalt ions where increasing the number n of water molecules above n = 7 allows one to built up an absorption band that is known when Co+ is solvated in liquid water. The two fragmentation techniques appear as complementary. (C) 2002 Elsevier Science B.V. All rights reserved.