microscopic parameters in the excited state of toluene and some of its haloderavatives

the ultraviolet-visible (uv) spectra of toluene, ortho-bromo and para-bromo toluene in different solvents have been studied. the electric dipole moments and polarizabilities in the molecular excited electronic states were determined. it was found that the electric dipole moments for the excited states (µ*) and the ground states (µ) of these compounds are equal, and the change in dipole moment is zero. this implies, in part, little or no change in potential energy surfaces of the ground and the excited states. the negative values obtained for the change in polarizabilities (??) for the lb state in various transitions indicate contraction in the excited state relative to the ground state, because the polarizability is proportional to the molecular volume.