Permanent Electric Dipole of Gas-Phase p-Amino Benzoic Acid

By coupling a matrix-assisted laser desorption source to an electric beam deflection setup, we have measured the permanent electric dipole moment of the isolated p-amino benzoic acid (PABA) molecule in the ground state along its principal axis. This is the first measurement of the electric dipole of an isolated push−pull molecule. The experimental value is compared to different calculations, and the accuracy of Hartree−Fock and density functional approaches to predict the electronic properties of π-conjugated systems is discussed.