John S. Winn
Professor of Chemistry
Professor Winn received SB degrees in Chemistry and Physics from M.I.T. in 1969 and a Ph.D. in Chemistry from the University of California at Berkeley in 1973 working in the area of ion-molecule scattering. Following two years of post-doctoral research at Harvard on van der Waals molecules, he returned to Berkeley to join the faculty. He joined the Dartmouth faculty in 1982.
Research Interests
Our research centers around the information on molecular structure and dynamics that can be attained from high resolution spectroscopy. Three experimental techniques-molecular beams, Fourier transform spectroscopy, and matrix isolation spectroscopy-are currently being used to study such problems. In one study, we have coupled our high resolution interferometric spectrometer to a 120 m path length multi-pass gas cell to study the overtone spectra of acetylene from the fundamental near 3000 cm–1 to overtones in the 15000 cm–1 region. We have been able to assign these spectra and analyze them in a way that allows better understanding of the coupling of energy among bending and stretching vibrational modes at these energies. In the matrix isolation work, we have used a new theoretical model of the infrared lineshape of species isolated in simple cryogenic solids to understand the packing of the matrix (solid Ar) around a simple linear solute. In the case of solvated OCS, comparisons of the theoretical lineshapes to the experimental data show two major matrix sites. In one, the site is described by the relaxation of a perfect Ar crystal with a double substitutional site for OCS. In the other, the site is more akin to the sequential addition of Ar after Ar to the OCS. The site structures are very similar in gross appearance, but they have dramatically different effects--a factor of ten--on the linewidth. We have extended this method to the study of pure CO in Ar as well as to CO fragments produced by photolysis in the matrix. We have shown, for example, that the CO fragment from OCS is in a very different environment from that around pure CO in an Ar matrix. In addition, photoejection of CO from metal carbonyls lead to a variety of sites with unique transition frequency shifts and widths.