Dr. Brian Vest (Postdoctoral Fellow)

Centre for Theoretical Chemistry and Physics Bldg.44, NZ Institute for Advanced Study Massey University (Albany Campus) Private Bag 102904 North Shore MSC, Auckland New Zealand Phone +64 9 414 0800 ext. 9622 Fax +64 9 443 9779 Email: B.Vest@massey.ac.nz

Research Interests

Transition metal halides have a vast number of uses in industry. These compounds are widely used as catalysts and in the lamp industry. They are also used in gas-transport systems for the chemical vapor deposition of metal complexes. Hence, a good understanding of their structural and electronic properties is imperative to improve these systems.
Structural determination of the first row transition metal dihalides in the gas-phase has been difficult and filled with controversy. Many of these molecules suffer from low-energy bending modes in the monomeric form. Since high temperatures are required for experimentalists to study these compounds in the gas-phase, their data are often complicated from the occupation of excited vibrational levels. Hence, it is quite difficult to obtain accurate bond distances and bond angles from infrared spectroscopy. Further complications arise from the presence of dimeric, trimeric, and tetrameric forms of these metal halides in the gas-phase and often lead to inaccurate experimental results in electron diffraction experiments. Since cluster contamination can be as high as 50% for some of these molecules, an accurate determination of the clusters' geometries and thermodynamic properties is necessary.
Theoretical calculations on the gas-phase transition metal dihalides are also filled with complications. The combination of significant s-d mixing and the strong p-donor properties of the halides result in many low-level, closely lying energy states. These energy states are very sensitive to the level of electron correlation as well as the level of relativistic effects considered. Failure to account for these two properties result in incorrect ground states being calculated. Each of these states also has vastly different electronic and geometrical properties. The barrier of inversion for bending these molecules is often very small and results in a very shallow potential well. The small barrier makes it difficult to determine a true minimum or even know if the monomers are bent. Many theoretical studies have been done on the monomers of the first-row transition metal dihalides; however, very little is known about the properties of the higher order clusters they form in the gas phase.
This research project focuses on the dihalides of chromium (CrX2) and iron (FeX2); X = F, Cl, Br, I. The ground state geometries and energies of the monomers, dimers, trimers, and tetramers will be determined and compared with any available experimental/theoretical data. An examination of the clusters' thermodynamic properties will provide clues as to the relative proportions in the gas phase. These calculations will provide an important step for both experimentalists and theoreticians in understanding these deceptively simple molecules.
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