2-COLOR LASER PHOTOELECTRON-SPECTROSCOPY OF ELECTRONICALLY EXCITED CATIONS - VIBRATIONALLY RESOLVED SPECTRUM OF THE (2)A(2) STATE OF ANILINE

Two-color ionization photoelectron spectra of aniline via the neutral molecule vibronic states S-1(0(0)(0)) and S-1(6a(0)(1)) are presented. The intermediate vibrational states of the S-1 manifold are prepared by a picosecond laser pulse near 290 nm, and the subsequent ionization is induced by a time delayed 200 nm laser pulse. Mixing of molecular orbitals leads to an unexpecttd optical transition from the S-1(B-1(2)) State to the electronically excited (2)A(2) State of the cation. The ionization potential of the latter state is found to be 9.031 +/- 0.010 eV, slightly higher than the He I photoelectron spectroscopy value reported in the literature. Comparison of the spectra obtained via the two different vibronic resonances allows us to assign a 65 meV progression of vibrational peaks in the cation (2)A(2) spectrum to the 6a mode. The partial ionization cross section to the excited ion (2)A(2) State is measured to be 7 +/- 2% relative to the cross section to the ionic ground state. INDO/l calculations suggest that the optical transition to the (2)A(2) State is due to initial state configuration interaction, i.e., a mixing of the S-1 state with higher electronic states in the neutral molecule.