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Summary

Our research combines theory with experiment. One focus of my research addresses the question: What happens when molecules are energized by light? Our current experiments involve both one- and two-laser excitation of a supersonic jet in which high-pressure gas is expanded through an orifice to reach supersonic speed and becomes very cold. Molecular spectra are greatly simplified at the low temperature of the jet, and high resolution becomes possible.

From these experiments we are getting new information on some very well studied molecules, that could never be found from traditional spectra. The result is a recalibration of our ideas on potential surfaces for both ground and excited states of polyatomic molecules. For example, our ideas show that for molecules containing methyl groups (e.g., acetone and dimethyl ether) our view of methyl rotation has been conceptually deficient and that new ways of thinking about rotation are needed.

Another component of our research addresses, through high-level ab initio supercomputer computations, the question: Where do potential barriers come from? These calculations indicate that steric repulsion is not generally the origin of torsional barriers. The understanding of the relationship between electronic and molecular structure that we have obtained from these studies has potential for drug design.

Methyl Torsion in Propene Initiates Ethylenic Hydrogen Wagging and Twisting. L. Goodman, J. Leszczynski and T. Kundu. J. Am. Chem. Soc.115, 11991 (1993).

Torsional Vibrations in Jet Cooled Acetaldehyde. H. Gu, T. Kundu, and L. Goodman. J. Phys. Chem. 97, 7194 (1993).

Energetic Consequences of the Multidimensional Nature of Internal Rotation in Acetaldehyde, L. Goodman, T. Kundu, and J. Leszczynski, J. Am. Chem. Soc. 117, 2082 (1995).

Where does the Dimethyl Ether Internal Rotation Barrier Come From? L. Goodman and V. Pophristic, Chem. Phys. Lett. 259, 287 (1996).

Getting the Shape of Methyl Internal Rotation Potential Surfaces Right. L. Goodman, T. Kundu and J. Leszczynski, J. Phys. Chem. 100, 3026 (1996).

Role of Lone-Pairs in Internal Rotation Barriers, V. Pophristic, L. Goodman, and N. Guchhait, J. Phys. Chem. 101, 4290 (1997).

Density Functional Theory of Formaldehyde Harmonic Vibrational Spectrum, J. Leszczynski, L. Goodman, and J. S. Kwiatkowski, Theor. Chem. Accounts, 97, 195 (1997).

Coupled Cluster and Density Function Calculations of Methanol Harmonic
Force Constants, J. Florian, J. Leszczynski, B. G. Johnson, and L. Goodman, Mol. Phys. 91, 439 (1997).

Flexing Analysis of Steric Exchange Repulsion Accompanying Ethane Internal Rotation, L. Goodman and H. Gu, J. Chem. Phys. 109, 72 (1998).

Two-Color ZEKE-PFI Spectroscopy of the Acetone n-Radical Cation: the a₂ Torsional Vibration, R. T. Wiedmann, L. Goodman, and M. G. White, Chem. Phys. Lett. 293, 391 (1998).

Rotational Barriers: Barreir Origins, L. Goodman and V. Pophristic, Chapter in The Encyclopedia of Computational Chemistry, Vol. IV pp 2577-98, Ed. P.v. R. Schleyer, Wiley, (1998).

Flexing Analysis of Ethane Internal Rotation Energetics, L. Goodman, H. Gu, and V. Pophristic, J. Chem. Phys. 110, 4268 (1999).

Origin of Methyl Rotational Barriers, L. Goodman and V. Pophristic and F. Weinhold, Accounts of Chemical Research December (1999).

Acetone n-radial cation internal rotation spectrum. The torsional surface, D.A. Slea, L. Goodman, and M.G. While, J. Chem. Phys, in press.

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