Research

For recent projects click here  

The AirUCI Collaborative Research
I am involved in a long-term international project within the scope of the AirUCI Environmental Molecular Sciences Institute funded by U.S. National Science Foundation that is focused on understanding processes at the air-water interface in the atmosphere and their impacts on air quality and global climate change. This institute, directed by Prof. Barbara Finlayson-Pitts of University of California, Irvine (UCI), involves her research group as well as those of Professors R. Benny Gerber, John C. Hemminger, Sergey Nizkorodov and Douglas J. Tobias in the UCI Department of Chemistry, Prof. Donald Dabdub in the UCI Department of Mechanical & Aerospace Engineering, Prof. Pavel Jungwirth and myself of our Department of Molecular Modelling, Prof. Leon Phillips of the University of Canterbury, New Zealand, and Prof. Yulii Gershenson of the Russian Academy of Sciences. In addition, nine scientists from the U.S. Department of Energy National Laboratories (Pacific Northwest National Laboratory, Lawrence Berkeley National Laboratory and Lawrence Livermore National Laboratory) participate as collaborators. In the Institute, experimentalists, theoreticians and chemical kinetics and molecular modellers are combined to provide a unique approach to understanding processes at the air-water interface and their implications for atmospheric chemistry.

Using molecular dynamics simulations, I study with a molecular resolution the structure and properties of aqueous interfaces as well as various aspects of processes taking place at liquid surfaces. In one of our current projects, we model the uptake of water vapor, hydroxyl radical and ozone by liquid water and aqueous salt solutions. The figure below shows schematically the possible outcomes of a gas phase molecule collision with a liquid surface.

From a large set of such scattering trajectories, we were able to calculate the thermal and mass accommodation coefficients for a water molecule and a hydroxyl radical at liquid water. The thermal accommodation coefficient is defined as the probability that a molecule impinging on the interface from the gas phase side reaches the thermal equilibrium with the liquid. Analogically, the mass accommodation coefficient determines the probability that a molecule impinging on the interface enters into the bulk liquid phase. These two parameters are crucial for modeling the transport of molecules across the air/water interface, however, their experimental determination is a complicated task, as the coefficients are not directly measurable quantities. On the contrary, their determination from a molecular dynamics simulation is straightforward based on the observed trajectory statistics.

M. Roeselova, J. Vieceli, L. X. Dang, B. C. Garrett, D. J. Tobias: Hydroxyl radical at the air/water interface. J. Am. Chem. Soc. 126 (2004) 16308-16309

J. Vieceli, M. Roeselova, D. J. Tobias: Accommodation coefficients for water vapor at the air/water interface. Chem. Phys. Lett. 393 (2004) 249-255

J. Vieceli, M. Roeselova, N. Potter, L. X. Dang, B. C. Garrett, D. J. Tobias: Molecular dynamics simulations of atmospheric oxidants at the air-water interface: Solvation and accommodation of OH and O₃. J. Phys. Chem. B 109 (2005) 15876-15892

Another of our projects concerns atmospheric chemistry of sea-salt aerosols. This picture shows, how sea-salt aerosols consisting of concentrated salt solution particles (microdroplets, microbrines) are created by the breaking waves...

... and this is a picture of the aerosol chamber laboratory of Prof. Barbara Finlayson-Pitts at the University of California in Irvine, where the reactivity of the aerosols is studied under controlled laboratory conditions.

In one of their experimental studies, the Finlayson-Pitts group have shown that molecular chlorine (Cl2) or bromine (Br2) are produced from a reaction of OH with deliquesced NaCl or NaBr particles. In the case of NaBr aerosol, Br2 can also be produced from a reaction of ozone with the NaBr particles. In order to help elucidating the reaction mechanism, we carried out molecular dynamics simulations, in which we have been looking at interaction of OH and O3 with 6M NaCl and NaBr solutions. The picture below shows a patch of 30-by-30 Angstroms of the surface of the two solutions (6M NaCl solution on the left, 6M NaBr solution on the right).

Based on the experimentally measured kinetics and a chemical kinetics computer model, a heterogeneous reaction between the gas phase oxidant (OH or ozone) and the halide ion exposed on the surface of the solution was proposed. With our MD simulations, we were able to support the feasibility of this hypothesis by observing a strong preference for partial (surface) solvation for both OH and O3 as well as their frequent contacts with halide ions in the interfacial region. The picture below shows a hydroxyl radical (its oxygen depicted in blue) in contact with a chloride ions at the surface of the 6M NaCl solution. (Color coding same as above.)

M. Roeselova, D. J. Tobias, R. B. Gerber, P. Jungwirth: Impact, accommodation, and trapping of hydroxyl radical and ozone at aqueous salt aerosol surfaces: A molecular dynamics study. J. Phys. Chem. B 107 (2003) 12690-12699

S. W. Hunt, M. Roeselova, W. Wang, L. M. Wingen, E. M. Knipping, D. J. Tobias, D. Dabdub, B. J. Finlayson-Pitts: Formation of molecular bromine from the reaction of ozone with deliquesced NaBr aerosol: Evidence for interface chemistry. J. Phys. Chem. A 108 (2004) 11559-11572

 

Electron Photodetachment in Halide-Water Clusters

My Ph.D. work in the group of Prof. Pavel Jungwirth concerned the ultrafast dynamics of neutral halogen-water clusters X(H2O)n following the electron photodetachment in their anionic X-(H2O)n precursors which I studied using computer simulations. I used the Wigner trajectories approach, i.e. a combination of quantum initial state and classical molecular dynamics. In the case of the smallest cluster, X...H2O, also a numerically exact 3-D quantum propagation was feasible which allowed us to model the experimental photoelectron (ZEKE) spectra. The picture below illustrates the unusual dynamics following electron photodetachment in the chloride-water complex. For more detailes, see my thesis (pdf file, 3.9 MB).

M. Roeselova, M. Mucha, B. Schmidt, P. Jungwirth: Quantum dynamics and spectroscopy of electron photodetachment in Cl-...H2O and Cl-...D2O complexes. J. Phys. Chem. A 106 (2002) 12229-12241

M. Roeselova, U. Kaldor, P. Jungwirth: Ultrafast dynamics of chlorine-water and bromine-water radical complexes following electron photodetachment in their anionic precursors. J. Phys. Chem. A 104 (2000) 6523-6531

P. Jungwirth, M. Roeselova, R. B. Gerber: Optimal coordinates for separable approximations in quantum dynamics of polyatomic systems: Coordinate choice criteria and error estimates. J. Chem. Phys. 110 (1999) 9833-9841

M. Roeselova, G. Jacoby, U. Kaldor, P. Jungwirth: Relaxation of chlorine anions solvated in small water clusters upon electron photodetachment: The three lowest potential energy surfaces of the neutral Cl...H2O complex. Chem. Phys. Lett. 293 (1998) 309-316  

Jahn-Teller Effect in Cyclobutadiene Radical Cation

Before my Ph.D. studies, I was involved in ab initio quantum chemistry calculations. My main project in this field concerned the electronic structure and rearrangements of Jahn-Teller active organic radical cations (C4H4.+).

V. Hrouda, M. Roeselova, T. Bally: The C4H4.+ potential energy surface. 3. The reaction of acetylene with its radical cation. J. Phys. Chem. 101 (1997) 3925-3935

M. Roeselova, T. Bally, P. Jungwirth, P. Carsky: Cyclobutadiene radical cation. An ab initio study of the Jahn-Teller surface. Chem. Phys. Lett. 234 (1995) 395-404