Ab initio studies of O2-(H2O)n and O3-(H2O)n anionic molecular clusters, n≤12

An ab initio study of gaseous clusters of O₂^&minus; and O₃^&minus; with water is presented. Based on thorough scans of configurational space, we determine the thermodynamics of cluster growth. The results are in good agreement with benchmark computational methods and existing experimental data. We find that anionic O₂^&minus;(H₂O)_<i>n</i> and O₃^&minus;(H₂O)_<i>n</i> clusters are thermally stabilized at typical atmospheric conditions for at least <i>n</i> = 5. The first 4 water molecules are strongly bound to the anion due to delocalization of the excess charge while stabilization of more than 4 H₂O is due to normal hydrogen bonding. Although clustering up to 12 H₂O, we find that the O₂ and O₃ anions retain at least ca. 80 % of the charge and are located at the surface of the cluster. The O₂^&minus; and O₃^&minus; speicies are thus accessible for further reactions. We consider the distributions of cluster sizes as function of altitude before finally, the thermodynamics of a few relevant cluster reactions are considered

Structures and reaction rates of the gaseous oxidation of SO₂ by an O₋₃ (H₂O)₀₋₅ cluster – a density functional theory investigation

Based on density functional theory calculations we present a study of the gaseous oxidation of SO₂ to SO₃ by an anionic O₃^&minus;(H₂O)_<i>n</i> cluster, <i>n</i> = 0–5. The configurations of the most relevant reactants, transition states, and products are discussed and compared to previous findings. Two different classes of transition states have been identified. One class is characterised by strong networks of hydrogen bonds, very similar to the reactant complexes. The other class is characterised by sparser structures of hydration water and is stabilised by high entropy. At temperatures relevant for atmospheric chemistry, the most energetically favourable class of transition states vary with the number of water molecules attached. A kinetic model is utilised, taking into account the most likely outcomes of the initial SO₂ O₃^&minus;(H₂O)_<i>n</i> collision complexes. This model shows that the reaction takes place at collision rates regardless of the number of water molecules involved. A lifetime analysis of the collision complexes supports this conclusion. Hereafter, the thermodynamics of water and O₂ condensation and evaporation from the product SO₃^&minus;O₂(H₂O)_<i>n</i> cluster is considered and the final products are predicted to be O₂SO₃^&minus; and O₂SO₃^&minus;(H₂O)₁. The low degree of hydration is rationalised through a charge analysis of the relevant complexes. Finally, the thermodynamics of a few relevant reactions of the O₂SO₃^&minus; and O₂SO₃^&minus;(H₂O)₁ complexes are considered

Photo- and Collision-Induced Isomerization of a Charge-Tagged Norbornadiene–Quadricyclane System

Molecular photoswitches based on the norbornadiene-quadricylane (NBD-QC) couple have been proposed as key elements of molecular solar thermal energy storage schemes. To characterize the intrinsic properties of such systems, reversible isomerization of a charge-tagged NBD-QC carboxylate couple is investigated in a tandem ion mobility mass spectrometer, using light to induce intramolecular [2 + 2] cycloaddition of NBD carboxylate to form the QC carboxylate and driving the back reaction with molecular collisions. The NBD carboxylate photoisomerization action spectrum recorded by monitoring the QC carboxylate photoisomer extends from 290 to 360 nm with a maximum at 315 nm, and in the longer wavelength region resembles the NBD carboxylate absorption spectrum recorded in solution. Key structural and photochemical properties of the NBD-QC carboxylate system, including the gas-phase absorption spectrum and the energy storage capacity, are determined through computational studies using density functional theory