Push-Pull Molecules in the Gas Phase:Stark-Effect Measurements of the Permanent Dipole Moments of p-Aminobenzoic Acid in Its Ground and Electronically Excited States

摘要

Stark effect measurements of the permanent electric dipole moments of p-aminobenzoic acid(PABA)in the gas phase are reported based on studies of its fully resolved S1<-S0 electronic spectrum in the presence of an electric field.Ground-state(So)PABA has mu=3.3 D,whereas excited-state(S1)PABA has mu=4.4 D.Despite PABA's reputation as a"push-pull"molecule,the photon-induced change in both the magnitude and orientation of mu is relatively small.Possible reasons for this behavior are discussed.