John P. Lowe
- Professor Emeritus of Chemistry
Research Interests
Quantum chemistry; relations between Huckel and LCAO-MO-SCF methods; MO approaches to chemisorption, catalysis, and cancer; theory of organic conductors; band structures of polymers; Graph Theory.
Molecular Orbital Studies of Carcinogenicity and of Periodic Structures
The general theme of Professor Lowe's research is finding the qualitative picture underlying molecular orbital calculations of chemical phenomena. A good example is his recent series of papers in the area of carcinogenicity of polycyclic aromatic hydrocarbons. These studies, performed in collaboration with Dr. B. D. Silverman of IBM, have shown interesting and useful relationships between a molecule's carcinogenic activity and such structural features as the presence of bends in the aromatic chain; the presence and positions of methyl substituents on the molecule; the presence of heteroatoms, like nitrogen, in the molecular framework; and the existence of odd-membered cycles in a molecule. The relationship (and essential agreement) of two seemingly different theories of carcinogenicity, the K-region theory and the bay-region theory, has been demonstrated.
When atoms combine to form huge periodic structures, like polymers, molecular orbitals become crystalline orbitals, and energy-level diagrams become energy-band diagrams. Just as it is often useful to understand how MO energies are affected by chemical substitution, it is desirable to understand how a polymer's energy bands are influenced by changes in chemical composition. Such changes can alter the electronic properties of polymers, an area of great current interest. Research on this question in Professor Lowe's group has led to an extremely simple, very general way to understand how chemical substitution in polymers affects band energies.
The surface of graphite is a quasi-two-dimensional periodic structure of great interest in chemistry and physics. When atoms chemisorb onto a graphite surface, they interrupt the p-electron conjugation. This means that different patterns of chemisorption will have different energies, even when the percent of coverage is the same. Professor Lowe's group has examined the relative stabilities of H-atom patterns on graphite as predicted by elementary MO theory using band theory and cluster models, and they have shown how the results relate to frontier orbital theory.
