David M. Hanson
Biochemistry and Cell Biology
Stony Brook University
United States of America
DAVID M. HANSON, joined as Professor of Department of Biochemistry and Cell Biology,The Stony Brook University School of Medicine.
Ask yourself the question, "What happens to a molecule when it absorbs around 300 eV of energy and a carbon 1s electron is ionized?" The common answer is " It flies apart!" This intuition is consistent with early studies that led to the term "Coulomb explosion," but new experiments have shown that the relaxation processes following such excitation can be highly selective. My research group is investigating the reasons for this selectivity and is exploring potential applications to microfabrication technology. This technology is directed at producing mechanical and electronic devices on the incredibly small scale of nanometers. The inner shell electrons in molecules are called core electrons, and many of these have binding energies of hundreds of electron volts and are localized to particular atoms in a molecule. This localization can lead to a very desirable result--atom selective photochemistry! Photons with these high energies lie in the soft X-ray region of the spectrum. Such photons can be used either to ionize the core electrons or excite them to different kinds of bound states. The absorption spectrum of a molecule in the soft X-ray region therefore consists of sharp structure due to the bound states, and broad features due to the ionization. The sharp structure and the details of the broad features are very sensitive probes of the bonding properties of molecules and are being used to learn about the nature of bonds in molecules chemisorbed on surfaces. Such knowledge is necessary, for example, to understand the catalytic activity of solids.