Stark effects in gas-phase electronic spectra.  Dipole moment of aniline in its excited S(1) state. 
Measurements of the Stark effect on the rotationally resolved S(1)<--S(0) fluorescence excitation spectrum of aniline are 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 approximately 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.