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		Philip M. Johnson Professor B.S., 1962, University of Washington; Ph.D., 1967, Cornell University; Postdoctoral Fellow, University of Chicago, 1966-68; Visiting Fellow of the Joint Institute for Laboratory Astrophysics, 1976-77; Guggenheim Fellow, 1982-83; Fellow of the American Physical Society. (631) 632-7912 Email: philip.johnson@sunysb.edu Publications

	PHYSICAL CHEMISTRY: MOLECULAR SPECTROSCOPY AND PHOTOPHYSICS The extremely high light levels available in pulsed lasers have created a rapid development in the understanding of the structure and dynamics of gas phase molecules and how they interact with the light. Our laboratory is actively involved in creating new techniques for the use of lasers in studying molecules and applying these techniques to prototype molecular systems. Many of the methods we have developed involve the ionization of the target molecules. In the high light flux from pulsed lasers the molecules keep absorbing the light until they lose an electron. The details of this electron loss, such as the wavelength dependence and the energy of the departing electron, give a great deal of information about both the bound and ionic states of the target molecule as well as indications about the photophysics of the various excited states. The gas phase systems we study range from small molecules such as nitric oxide and carbon dioxide to larger species including aromatics and molecular clusters. We have frequently discovered new excited electronic states of these systems, observed novel photochemical pathways, seen new physical phenomena, and refined our knowledge of the vibrational motions and geometric structures of excited states. In our analyses of the molecular spectra we are often guided by theoretical electronic structure calculations. Various techniques we have developed are in use in laboratories throughout the world in such practical applications as the determination of the details of combustion processes and the analysis of atmospheric gases. Recent developments in lasers and computers promise to enable even more powerful experiments to get at the details of molecular structure, photochemistry, and photophysics. Recently we have been exploiting the properties of Rydberg molecules (where one electron is almost removed from the molecule and placed into a giant orbit) to develop new methods for obtaining the high resolution spectra of molecular cations. The exploitation of Rydberg molecules has enabled orders-of-magnitude increases in the resolution available for recording the spectra of molecular ions. A newly developed technique is called photoinduced Rydberg ionization spectroscopy (PIRI), providing high resolution access to the spectroscopy of the excited electronic states of ions. To accomplish this, we create a highRydberg state just below an ionic threshold and then excite the ion core. The spectrum of the resulting photoinduced autoionization is therefore basically that of the ion and has the resolution of the laser, while providing the information superior to a photoelectron spectrum. Photoinduced Rydberg Ionization Spectroscopy

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