Photodissociation Studies on(H2O)n+(n=2-5)Clusters at 308 nm
The photodissociation dynamics of small(H2O)n+(n=2-5)clusters have been studied at 308 nm using a high resolution cryogenic cylin-drical ion trap velocity map imaging spectrome-ter.Time-of-flight mass spectra and images of ionic photofragments are recorded.(H2O)2+clusters dissociate to yield H3O+and H2O+photofragments,indicating the presence of both proton-transferred(H3O+-OH)and hemibond-ed(H2O-OH2)+structures for the dimer clus-ter.(H2O)n+(n=3-5)clusters prevailingly dis-sociate to the H+(H2O)n-2,…,1 photofragments by losing both of OH and H2O components,and the(H2O)5+cluster shows an additional channel to produce H+(H2O)4 by only losing OH.The former suggests the(H2O)n-2H3O+OH structures for the(H2O)n+(n=3-5)clus-ters,while the latter suggests in(H2O)5+that,the H3O+core and OH are separated by H2O.The results elucidate the structure progresses of small(H2O)n+clusters.The experi-mental images yield negative and small values for the anisotropy parameters of photofrag-ments,indicating that(H2O)n+(n=2-5)clusters undergo vertical electronic transitions up-on photon absorption followed by slow dissociation,and lead to highly internally excited photofragments.
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