Experimental Determination of Vibrational Potential Energy Surfaces and Molecular Structures in Electronic Excited States

Abstract

For more than three decades far-infrared and Raman spectroscopies, along with appropriate quantum mechanical computations, have been effectively used to determine the potential energy functions which govern the conformationally important large-amplitude vibrations of nonrigid molecules. More recently, we have utilized laser-induced fluorescence (LIF) excitation spectroscopy and ultraviolet absorption spectroscopy to analyze the vibronic energy levels of electronic excited states in order to determine the potential energy surfaces and molecular conformations in these states. Transitions from the ground vibrational state in an S0 electronic state can typically be observed only to several excited vibronic levels. Hence, the LIF of the jet-cooled molecules generally provides data on only a few excited state levels. Ultraviolet absorption spectra recorded at ambient temperatures, however, often provide data on many additional excited vibronic levels. However, these can only be correctly interpreted if the elec...