Photodetachment and photofragmentation pathways in the [(CO2)(2)(H2O)(m)](-) cluster anions

摘要

The mass-selected [(CO2)(2)(H2O)(m)](-) cluster anions are studied using a combination of photoelectron imaging and photofragment mass spectroscopy at 355 nm. Photoelectron imaging studies are carried out on the mass-selected parent cluster anions in the m=2-6 size range; photofragmentation results are presented for m=3-11. While the photoelectron images suggest possible coexistence of the CO2-(H2O)(m)CO2 and (O2CCO2)(-)(H2O)(m) parent cluster structures, particularly for m=2 and 3, only the CO2- based clusters are both required and sufficient to explain all fragmentation pathways for m >= 3. Three types of anionic photofragments are observed: CO2-(H2O)(k), O-(H2O)(k), and CO3-(H2O)(k), k <= m, with their yields varying depending on the parent cluster size. Of these, only CO2-(H2O)(k) can potentially result from (O2CCO2)(-)(H2O)(m) parent structures, although an alternative mechanism, involving the dissociation and recombination of the CO2- cluster core, is possible as well. The O-(H2O)(k) and CO3-(H2O)(k) channels are believed to be triggered by the dissociation of the CO2- cluster core. In the CO3-(H2O)(k) channel, seen only in the range of m=3-6, the CO2- core dissociation is followed by an intracluster association of nascent O- with the solvent CO2. This channel's absence in larger clusters (m > 6) is attributed to hindrance from the H2O molecules. (c) 2006 American Institute of Physics.