Excess Energy-Dependent Photodissociation Probabilities for O2- in Water Clusters: O2-.cntdot.(H2O)n, 1 .ltoreq. n .ltoreq. 33

Abstract

We report the branching ratios, #, for photodissociation of 0 2 -in water clusters, 02-*(H~0)~, as a function of excess energy [over the bond energy, E,,,,,, = hv -D0(02-)] and cluster size, 1 I n I 33. The twodimensional #(Eexcess, n) "dissociation" surface is generated from a series of measurements over the range 0 I E,,,,,, I 1.8 eV and displays features attributable to attractive forces at small E,,,,,, and repulsive interactions at high E,,,,,,. This #(Eexcess, n) surface is essentially independent of cluster size in the range 18 I n I 33, where all clusters are characterized by a single #(Eexcess) curve. Similarly, #(Eexcess, n) becomes independent of E,,,,,, at high E,,,,,, (21 eV) with a characteristic #(n) dependence. At both large E,,,,,, and large n, #(Eexcess, n) displays a plateau at about 0.70 which is very weakly dependent on both E,,,,,, and n. We interpret the shape of the surface in the context of a model recently developed by Apkarian and co-workers (J. Phys. Chem. 1994,98,7966) to explain the excess energy-dependent dissociation yields for small molecules in rare-gas matrices.

Visible spectrum photofragmentation of O3−(H2O)n, n ≤ 16

“…This result is very similar to the solvent binding energy upper limit, or the average monomer evaporation energy, found for O 2 − (H 2 O) n , 470 meV. 35 The O − -OO bond dissociation limit, D 0 , within the cluster can be determined through analysis of the average number of solvent molecules lost for the O − -based product channel, also shown in Fig. 5 35 These differences are attributed to the change in solvation energy of the parent anion compared to the dissociation products.…”

Photodetachment, photofragmentation, and fragment autodetachment of [O2n(H2O)m]− clusters: Core-anion structures and fragment energy partitioning

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] The above cluster types have been studied extensively using a variety of experimental techniques, including mass spectrometry, 16 photofragment action, and translational spectroscopy, 3,5,8 as well as photoelectron spectroscopy. 2,6,9,11,12 Most studies have focused either on the oxygen clusters, O 2n − , 2,3,6-11 or hydrated superoxide, O 2 − ͑H 2 O͒ m .…”

“…2,6,9,11,12 Most studies have focused either on the oxygen clusters, O 2n − , 2,3,6-11 or hydrated superoxide, O 2 − ͑H 2 O͒ m . 4,5,12 The experiments on O 2n − have demonstrated the formation of O 4 − , which has been invoked as a core anion representing a structurally distinct species within these clusters. 17 Given the small dissociation energy of O 4 − ͑0.455 eV͒, 18 it is of interest whether its identity is preserved under hydration, which is characterized by strong ionic hydrogen-bonding interactions, often well in excess of the above dissociation energy of O 4 − .…”

“…Selected binding energies from previous studies are summarized in Table I. Hydrated superoxide cluster anions, O 2 − ͑H 2 O͒ m , have also been studied. 5,12,15 In the photodissociation of O 2 − ͑H 2 O͒ m , m Յ 33, examined over the range of 200-300 nm, Lavrich et al 5 observed two different anionic pathways: dissociation of the O 2 − core to form atomic oxygen anion and dehydration. The dehydration channel was found to favor longer wavelengths and larger clusters, while O 2 − dissociation dominated at shorter wavelengths and in smaller clusters.…”

An ab initio molecular dynamics study of the hydrogen bonded structure, dynamics and vibrational spectral diffusion of water in the ion hydration shell of a superoxide ion

“…Different spectroscopic studies such as high pressure mass spectrometry [9], photoelectron and photofragment spectroscopy [10,11], infrared spectroscopy [12] suggest that the most stable superoxidewater cluster consists of two dimeric water subclusters on each side of O À 2 forming a tetra-coordinated geometry. Theoretically, the tetra-coordinated structure is found as the highly symmetric and stable structure using density functional theory (DFT) with a plane wave basis set [13].…”