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Sean A. Peebles, Ph.D.

Associate Professor - Physical Chemistry

B.Sc., University of Exeter (UK), 1992
Ph.D., University of Exeter (UK), 1995
EIU, 2001

Courses Taught

CHM 1310, 1410, 1510 General Chemistry I, II
CHM 1315, 1415, 1515 General Chemistry Laboratory I, II
CHM 3910 Physical Chemistry I (Thermodynamics)
CHM 3915 Physical Chemistry Laboratory
CHM 3920 Physical Chemistry II (Quantum Chemistry)
CHM 4770 Molecular Spectroscopy
CHM 5300 Graduate Molecular Spectroscopy

Click here for Dr. Peebles' personal page

Research Interests

My current research interests focus on the characterization of weakly bound complexes via Fourier-transform microwave spectroscopy and theoretical methods. The spectroscopic studies utilize a Fourier-transform microwave spectrometer. This technique involves the supersonic expansion of a gas mixture (in argon or helium/neon) into an evacuated vacuum chamber where the molecules are subsequently probed by microsecond pulses of microwave radiation. The adiabatic cooling process cools the molecular expansion to just a few degrees kelvin and hence allows isolation of very weakly bound complexes, effectively freezing them out of the gas mixture and providing no mechanism by which they can fall apart.

Currently, I am interested in the study of weak complexes that have the potential to form so-called C-H hydrogen bonds. These types of forces are considerably weaker than the conventional hydrogen bonds that are observed to form between atoms like N-H..O or O-H..O.  Despite their very weak nature, it is important to study such interactions and quantify their effects to understand their influence on important biological processes such as protein folding and carbohydrate structures. More details of the experimental aspects of my research may be found on the following page http://ux1.eiu.edu/~cfsap/microwave.htm      

The theoretical studies involve both semi-empirical and ab initio calculations of the structures and properties of molecules and complexes, with a particular focus on the changes in various molecular properties that occur upon complexation (such as bond lengths, electric field gradients, barriers to rotation of methyl groups etc.). For these calculations we utilize the Department of Chemistry Tru64 Unix workstation as well as a dedicated PC in my lab. The theoretical computations complement the spectroscopic work and aid in spectral assignment as well as providing a means to understanding the balance of forces that lead to the geometries that we observe for the weak complexes studied.      

The long term goals of my research are to formulate a better understanding of the balance of forces responsible for the geometries of molecular clusters, ultimately leading to a quantitative understanding of the interactions in macroscopic condensed phases.

Representative Publications (undergraduate coauthors underlined)

• Rotational Spectrum, Structure and Modeling of the OCS-CS₂ van der Waals Complex, J.J.Newby, M.M. Serafin,* R.A. Peebles and S.A. Peebles, Phys. Chem. Chem. Phys., 7, (2005), 487-492.
• The heavy atom structure of 3-butyn-1-ol from microwave spectroscopy and an ab initio investigation of the conformers, E.D. Slagle, R.A. Peebles, S.A. Peebles, J. Mol. Struct., 693, (2004), 167-174.
• The Dimethyl Ether-OCS dimer: Rotational Spectrum, Structure and Ab Initio calculations, J.J.Newby, R.A. Peebles and S.A. Peebles, J. Phys. Chem. A, 108, (2004), 7372-7378.
• Structure of the Dimethyl Ether-CO₂ van der Waals Complex from Microwave Spectroscopy, J.J.Newby, R.A. Peebles and S.A. Peebles, J. Phys. Chem. A, 108, (2004), 11234-11240.
• The microwave spectrum, ab initio analysis, and structure of the fluorobenzene-hydrogen chloride complex, M.E. Sanz, S. Antolinez, J.L. Alonso, J.C. Lopez, R.L. Kuczkowski, S.A. Peebles, R.A. Peebles, F.C.Boman, E. Kraka, D. Cremer, J. Chem. Phys., 118, (2003), 9278-9290. 
• Microwave Spectra and Molecular Structures of (Z)-Pent-2-en-4-ynenitrile and Maleonitrile, R.J. Halter, R.L. Fimmen, R.J. McMahon, S.A. Peebles, R.L. Kuczkowski and J.F. Stanton, J. Am. Chem. Soc., 123, (2001), 12353-12363.