Resonance Two-Photon Ionization Spectroscopy of the Aniline Dimer

The resonance two-photon ionization (R2PI) spectra of the jet-cooled aniline dimers (An- d 0 ) 2, (An- d 5 ) 2, and (An- d 7 ) 2 have been recorded; the first 225 cm -1 region above the (An- d 0 ) 2 origin was also reproduced by fluorescence excitation spectroscopy. Relatively sharp structure near the origin of the local excited state is attributed to intermolecular modes, perhaps of multiple conformers. Broader features at higher energies are assigned to symmetric ring modes coupled to an underlying excimer state. The dispersed fluorescence spectrum excited at the dimer electronic origin suggests that excimer formation occurs soon after the local excited state is pumped. Molecular dynamics simulations support the inference from the spectroscopic observations that hydrogen bonding governs the structure of the aniline dimer.