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

The mass-selected [(CO2)2(H2O)m]− cluster anions are studied using a combination of photoelectron imaging and photofragment mass spectroscopy at 355nm. 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)mCO2 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.