Stark effects in gas-phase electronic spectra.: Dipole moment of aniline in its excited S1 state

Measurements of the Stark effect on the rotationally resolved S-1<--S-0 fluorescence excitation spectrum of aniline an reported, providing quantitative information about the degree of charge transfer in the electronic transition. We find that <mu>(a)(S-1) = 2.801 +/- 0.007 D, a value that is similar to 150% larger than the ground state, mu (a)(S-0) = 1.129 +/- 0.005 D. The enhanced value of the dipole moment in the S-1 state is attributed to more efficient electron donation by the quasi-planar amino group to the aromatic ring.