Structures and Vibrational Frequencies of Pure Halocarbon Clusters, and Mixed Clusters with Water

Principal Investigator

Gad Fischer

Chemistry

The Faculties

The adverse environmental effects of the halocarbons are well documented. Not only are they destructive of the stratospheric ozone layer but they are also powerful greenhouse gases. Although considerable data on the infrared absorption by these molecules has been reported recently, little is known about the role played by dimers and larger clusters of these molecules, and their concentrations in the atmosphere. The low temperatures encountered at high altitudes favour the formation of clusters.

Co-Investigators

Xiaolin Cao

Chemistry

The Faculties


Projects

u54 - PC

What are the results to date and the future of the work?

The initial approach to this project involved characterization of the monomer species of the perfluoro cycloalkanes. High level ab initio calculations, (HF/6-31G*, MP2/6-31G* and B3LYP/6-31G*), on the ground state optimized geometry and force field have been completed for perfluorocyclobutane. Barrier heights to the ring-puckering motion have been determined from molecular orbital calculations, and together with the calculated puckering vibrational frequency have been used to model the infrared spectrum with a quadratic-quartic potential. An explanation has been obtained for the lack of puckering structure in the infrared spectrum. Calculations, but at a lower level, have yet to be undertaken for perfluorocyclohexane, and for the cluster molecules. A sample calculation on a dimer molecule of purine at the HF/6-31G* and B3LYP/6-31G* levels proved successful.

What computational techniques are used?

The calculations were carried out for the electronic ground state with the GAUSSIAN molecular orbital programs: HF, MP2, and B3LYP all with the 6-31G* basis. Optimized geometries and vibrational frequencies were determined under two different symmetry constraints.

Publications

G. Fischer, R.L. Purchase and D.M. Smith,The ring-puckering motion in perfluorocyclobutane, J. Mol. Struct. in press

- Appendix A