CALCULATIONS OF THE ENERGIES AND GEOMETRIES OF THE GROUND AND 1ST EXCITED-STATES OF PHENYLALANINE AND TYROSINE

We attempt to interpret the fluorescence of phenylalanine and tyrosine from ab initio calculations of the ground states and the lowest excit ed singlet states of the two molecules. We determine the energy minima and the optimized geometries of the molecular ground states from HF/6 -31G computations and the energy minima and optimized geometries of th e lowest excited singlet states from CIS/6-31G computations. All compu tations are based on the GAUSSIAN 92 program package. We try to explai n the nature of the excitation by comparing the geometries and charge densities of the ground and excited states of the two molecules.