In this project in the Physical Chemistry Program of the Chemistry Division, Professor Jaan Laane of Texas A. and M. University will study vibrational potential energy surfaces in electronically excited states of molecules in a supersonically cooled jet. Fluorescence excitation spectra and sensitized phosphorescence excitation spectra will be recorded for four-, five-, and six-membered ring compounds as well as for various carbonyl and aromatic molecules. A comparison with potential functions and conformations for ground singlet and excited singlet and triplet states will be made. Ab initio calculations will also be carried out to help provide a better theoretical basis for understanding the changes resulting from electronic excitation. %%% The study of large-amplitude vibrational motions of non-rigid molecules provides information about the forces and energies which govern the conformational changes in these floppy molecules, that is, the changes from one "stable" structure to another "stable" structure. This information can be described by a mathematical function called a potential energy surface. Information about the rate at which one structure will convert to another and back again is also provided by such studies. This project will gather information about potential energy surfaces of several types of non-rigid ring molecules, emphasizing the changes in the surfaces that occur when the molecule is supplied enough energy to excite an electron to higher energy states. Calculations will also be carried out to provide a theoretical basis for understanding the structural and potential energy changes resulting from electronic excitation.
