Faculty Interaction

Mónica Martínez-Avilés

Department of Chemistry
Purdue University

Brief Project Description:

The following calculations are part of the research work of Mónica Martínez-Avilés, a Ph.D. student in Professor Francisco's group in the Department of Chemistry at Purdue University. She is studying the kinetics and mechanisms involved in the atmospheric degradation of bromoethane, bromopropane and its by-products. These studies can shed light on the processes involved in events such as atmospheric ozone depletion and global warming.

Several Gaussian jobs comprised some of the calculations involved in determining the degradation mechanism of bromopropane. These jobs were very resource-intensive and used about 200 hours of wallclock time on 12 processors of a 16-processor POWER4 (1.7 GHz, 128 GB memory) IBM Regatta. The scratch files for these jobs used approximately 150 GB of disk space. These were among the most resource intensive jobs to be successfully completed at Purdue University. (Thanks to Professor Gerhard Klimeck for allowing us use of his IBM Regatta.)

As part of the agreements of the Montreal Protocol on Substances that Deplete the Ozone Layer, there has been an increasing interest in replacing chlorofluorocarbons (CFCs) and several other halocarbons. Bromopropane (BrCH2CH2CH3) has been considered as a replacement for HCFC-141b, a chlorofluorocarbon used as the active component in many industrial cleaning solvents. The proposed mechanism for the atmospheric oxidation of bromopropane has been studied via ab initio methodology using the Gaussian 03 suite of programs. The structure and energetics of the 58 species and transition states involved in the atmospheric oxidation of bromopropane was examined. From these calculations, reaction enthalpies (ΔH) and activation energies (Ea) were determined to characterize the potential energy surface of the proposed mechanisms for the complete atmospheric degradation. The studies revealed that the hydrogen abstraction from the beta carbon has the lowest activation energy barrier of all the possible abstractions, making this pathway the most energetically favored pathway for the atmospheric oxidation process. The calculations for the atmospheric degradation of bromopropane show that the major oxidation specie is bromoacetone (BrCH2C(O)CH3) which is the main component of tear gas. Other brominated species that result from the oxidation are BrCH2CH2C(O)H, BrC(O)CH2CH3 and BrC(O)H. Many of these species have not been identified in any of the experimental studies as yet. However, results from this work have provided new insight into how these species can be characterized.

Following is a figure illustrating the degradation mechanism of bromopropane.