Physical Chemistry Seminar: "Structural, Dynamical and Thermodynamic Properties of Water Clusters"

Abstract: 

Water clusters constitute an important class of chemical species due to their central role in many physico-chemical and biological processes, in particular, atmospheric processes. Their physical and chemical properties are particularly sensitive to size and finite-temperature effects, which makes them particularly difficult to characterize experimentally. This work was focused on the theoretical investigation of the structural, dynamical and thermodynamic properties as well as on the reactivity of various water clusters with the aim to implement appropriate modeling tools to enable a more detailed description of the systems. To do so, we used the parallel-tempering molecular dynamics approach that was coupled with calculations of energies and gradients carried out by the Self-Consistent-Charge Density-Functional based on Tight-Binding (SCC-DFTB) method. 

The three main areas were addressed during the work. In the first part, a detailed analysis of the structure of water clusters (H₂O)_nSO₄^2- and (H₂O)_nH₂SO₄ with n = 1-20 was performed. This study highlights the influence of the nature of the sulfur impurity on the hydrogen bond network of these species. 

The second part of this work was focused on the study of the “solid liquid” phase transition in various water clusters. In addition to the sulfur-containing water clusters mentioned above, we also investigated protonated water clusters containing from 19 to 23 water molecules. To better understand the phase transition mechanism, we considered various structural changes associated with the transition, such as the evaluation of the distributions of intermolecular angels and the evolution of the number of molecular rings in the cluster. We also characterized the phase transition through dynamical indicators such as the crossover frequency of the excess proton.

The last part of the work was devoted to the study of the influence of small water clusters (from 1 to 10 water molecules) on the recombination reaction between the H atom and the CO molecule. This reaction is the first step in the formation of simple oxygenated organic molecules in the interstellar medium. It is therefore of particular interest. Due to the analysis of collisional dynamics between H and CO and the calculation of effective reaction cross sections were shown that the presence of water molecules plays an important role in the HCO radical formation.

Speakers:

• Dr. Kseniia Korchagina (Schwartz Lab)

PRESENTER

Dr. Kseniia Korchagina, Schwartz Lab