Stephen D. Belair

On the interactions between atmospheric radicals and cloud droplets: A molecular picture of the interface

How gas-phase materials become incorporated with cloud droplets has been an intriguing subject for decades, and considerable work has been done to understand the interactions between closed-shell molecules and liquid water. The interactions between open-shell radical species and liquid-phase cloud droplets, however, are not well understood. To probe these interactions we used quantum chemistry calculations to predict the energetics of the hydroperoxy radical (HO2) in the presence of an (H2O)20 spherical water cage. Our calculations show that it is energetically favorable for the radical to bind to the outside of the cage. This configuration has the hydrogen and the terminal oxygen of the radical as its primary bonding sites. Free-energy calculations suggest that, at atmospheric conditions, there will be a partitioning between HO2 radicals that are surface-bound and HO2 radicals that dissolve into the bulk. This may have important ramifications for our understanding of radical chemistry and may lend insight into the role that clouds and aerosols play in atmospheric chemical processes.

Potential energy surface for the hydroperoxy and water (HO2·H2O) radical complex

A potential energy surface for the system of a hydroperoxy radical and a water molecule is presented. The surface was sampled using constrained density functional theory optimizations performed at the B3LYP level of theory using a 6–311 ++G(3df,3pd) basis set. The data points were fitted to an analytical function based on a common 4-point model for water and a 5-point model for the peroxy radical. A weighted least-squares fit of the parameters was performed using the nearest neighbour pivot method.

Hydrogen bonding in cubic(H2O)8andOH∙(H2O)7clusters

A systematic study is presented for OH{center_dot}(H{sub 2}O){sub 7} clusters derived from the cubic (H{sub 2}O){sub 8} octamer by replacing one water with a hydroxyl radical. The system is a prototype for atmospheric water clusters containing the environmentally important OH species, and for OH adsorbed at the surface of ice. The full set of 39 symmetry-distinct cubic OH{center_dot}(H{sub 2}O){sub 7} clusters is enumerated, and the structures are determined using ab initio quantum chemical methods. Graph invariants are employed to obtain a unified analysis of the stability and structure of cubic (H{sub 2}O){sub 8} and OH{center_dot}(H{sub 2}O){sub 7}, relating these physical properties to the various hydrogen-bond topologies present in these clusters. To accomplish this the graph invariant formalism is extended to treat a hydrogen bonding impurity within a pure water network.

Hydrogen bonding in cubic (H{sub 2}O){sub 8} and OH{center_dot}(H{sub 2}O){sub 7} clusters

A systematic study is presented for OH{center_dot}(H{sub 2}O){sub 7} clusters derived from the cubic (H{sub 2}O){sub 8} octamer by replacing one water with a hydroxyl radical. The system is a prototype for atmospheric water clusters containing the environmentally important OH species, and for OH adsorbed at the surface of ice. The full set of 39 symmetry-distinct cubic OH{center_dot}(H{sub 2}O){sub 7} clusters is enumerated, and the structures are determined using ab initio quantum chemical methods. Graph invariants are employed to obtain a unified analysis of the stability and structure of cubic (H{sub 2}O){sub 8} and OH{center_dot}(H{sub 2}O){sub 7}, relating these physical properties to the various hydrogen-bond topologies present in these clusters. To accomplish this the graph invariant formalism is extended to treat a hydrogen bonding impurity within a pure water network.

Hydrogen bonding in cubic (H_2O)_8 and OH∙(H_2O)_7 clusters

A systematic study is presented for OH{center_dot}(H{sub 2}O){sub 7} clusters derived from the cubic (H{sub 2}O){sub 8} octamer by replacing one water with a hydroxyl radical. The system is a prototype for atmospheric water clusters containing the environmentally important OH species, and for OH adsorbed at the surface of ice. The full set of 39 symmetry-distinct cubic OH{center_dot}(H{sub 2}O){sub 7} clusters is enumerated, and the structures are determined using ab initio quantum chemical methods. Graph invariants are employed to obtain a unified analysis of the stability and structure of cubic (H{sub 2}O){sub 8} and OH{center_dot}(H{sub 2}O){sub 7}, relating these physical properties to the various hydrogen-bond topologies present in these clusters. To accomplish this the graph invariant formalism is extended to treat a hydrogen bonding impurity within a pure water network.