Analytic ab initio-based molecular interaction potential for the BrO⋅H2O complex

Abstract

Radical halogen oxide species play important roles within atmospheric processes, specifically those responsible for the removal of O3. To facilitate future investigations on this family of compounds, RCCSD(T)/aug-cc-pVQZ-level electronic structure calculations were employed to generate individual-molecule optimized geometries, as well as to determine the global minimum energy structure for the BrO⋅H2O complex. This information facilitated the generation of several one-dimensional potential energy surface (PES) scans for the BrO⋅H2O complex. Scans were performed for both the ground state and the first excited state; this inclusion is due to a low-lying first electronic excited-state energy. These rigid-geometry PES scans were used both to generate a novel analytic interaction potential by modifying the existing Thole-type model used for water and to the fitted potential function. This interaction potential features anisotropic atomic polarizabilities facilitating appropriate modeling of the physics regarding the unpaired electron residing within the p-orbitals of the oxygen atom of the bromine oxide radical. The intention of this work is to facilitate future molecular dynamics simulations involving the interaction between the BrO radical and water clusters as a first step in devising possible novel chemistries taking place at the water interface of clouds within the atmosphere.

Communication: Interaction of BrO radical with the surface of water

“…Figure 2(a) shows the radial distribution functions (RDFs) for (BrO)Br· · ·O(water) and (BrO)O· · ·H(water). Interestingly, the results show that the RDF for (BrO)Br· · · O(water) exhibits a peak at the distance of r = 2.4 Å and a valley is at r = 2.8 Å, which is close to the (BrO)Br· · ·O(water) bond distance (2.8 Å) in the global-minimum configuration of the BrO·H 2 O complex at 0 K. 10,15,16 This result indicates that the interaction of (BrO)Br· · ·O(water) at the surface of a water slab is much weaker than that in the gas phase, due to the competitive interactions between (water)H· · ·O(water) and (BrO)Br· · ·O(water) in the water slab. On the other hand, the peak of the RDF for (BrO)O· · ·H(water) appears at r = 2.0 Å, consistent with the (BrO)O· · ·H(water) distance (2.0 Å) in the global-minimum configuration of the BrO·H 2 O complex at 0 K. 10,15,16 This result can be explained by the fact that water molecules tend to expose their H site at the air/water interface, which would favor the hydrogen bonding formation of (BrO)O· · ·H(water).…”

“…[1][2][3][4][5][6][7][8][9] In particular, bromine containing radical species have been suggested to be more active than the chlorine analogues in the destructive processes. 10 One set of reactions involving bromine [4][5][6] that are crucial to ozone depletion within the marine boundary layer are as follows:…”

“…On the other hand, it is widely accepted that hydrogen-bonded complexes with radicals and water play key roles in atmospheric reactions, especially at the surface of the water droplet. [5][6][7][8][9][10][11][12][13][14] The key species involved in the chemistry is the BrO·H 2 O complex. 10,15,16 Gálvez et al 15 have studied the equilibrium geometries, energies, and properties of the BrO hydrates by means of ab initio calculations.…”

“…16 In another study, Hoehn et al employed RCCSD(T)/aug-cc-pVQZ level electronic structure calculations to derive an analytic potential energy function for the interaction between a BrO radical and a water molecule. 10 Most studies of the BrO radical have been focused on the gas-phase interaction. Detailed information about the physico-chemical behavior of the BrO radical at the surface of atmospheric aerosols and cloud droplets is still not fully understood.…”