Spectroscopic Investigations of Vibrational Potential Energy Surfaces and Molecular Structures in Singlet and Triplet Electronic Excited States

Texas A&M Research Foundation, College Station TX

Investigators

Abstract

Abstract Proposal : CHE-0131935 PI : Laane, J. There has been great interest in potential energy surfaces (PESs) in recent years, particularly in those for electronic excited states, since they can provide a wealth of data on molecular structure, bonding, and photochemical and photophysical processes. However, very few experimental PESs, rigorously determined from vibronic data, have been reported. Several different spectroscopic methods will be used to map the vibronic energy levels for structurally and conformationally important vibrations. The computational methodology for kinetic and potential energy calculations will be applied to determine the PESs of several types of electronic excited states in several different kinds of molecules. For singlet states (generally S1) laser induced fluorescence (LIF) spectroscopy of jet-cooled molecules and ultraviolet absorption spectroscopy will be utilized to establish the vibronic levels while far-infrared and Raman spectra will provide the complementary ground state data. A time of flight mass spectrometer, which allows mass resolution, will be used for ionization detection and resonance enhanced multiphoton ionization (REMPI) studies. This will allow access to non-fluorescing states and to transitions forbidden in one-photon LIF studies. Two-color experiments will be carried out to study higher singlet states. Considerable use will be made of sensitized phosphorescence excitation spectroscopy (SPES) for studying triplet states. Aryl ketones will be thoroughly investigated as these molecules show strong phosphorescence and are thus ideal for SPES studies of triplet states. The triplet and higher singlet states for molecules in the indan family will also be investigated. Several molecules with unusual bonding properties, such as the anomeric effect, will also be studied in ground and excited states in order to ascertain the effect of the electronic transitions on the bonding and structure. Spectroscopic methods using lasers for the absorption of light will be used to study the structures and energies of molecules in both their normal and "excited" forms. The excited forms are produced when electrons are excited by light to attain higher energies. Photochemistry, such as photosynthesis, typically occurs only after molecules have been excited in this manner. The goal of this research is to characterize the excited molecules and to compare them to their normal forms. The results of this work can prove beneficial to a variety of areas based on the interaction of light with molecules, such as the development of solar energy devices or the design of photochemical reactions. Students and postdoctoral research associates will participate in this research and will receive training to prepare them for entry into the scientific/technical workforce.