One-photon and Two-photon Electronic Spectra of Two Caged Amines

Abstract

Abstract The one-photon fluorescence excitation and two-photon resonant multiphoton ionization spectra of the S1←S0 transition of 1,4-diazabicyclo[2.2.2]octane (DABCO) in a supersonic free jet have been obtained and analyzed. It was found from the vibrational analysis that the S1←S0 transition is one-photon forbidden, two-photon allowed and the one-photon absorption appears by the vibronic interaction between the S1 and S2 states through the e′ vibrations. In addition, from the fluorescence spectrum and the polarization studies of the two-photon spectrum using the two linearly polarized laser beams of different wavelengths, it was concluded that the S1 state is 1A1′. The sequence structure involving the low-frequency cage torsional vibration has been observed in the two-photon resonant multiphoton ionization spectra of DABCO and 1-azabicyclo[2.2.2]octane (ABCO). The potential functions with respect to the torsional motion for both ground and excited states have been determined by utilizing the observed vibrational levels. It was found that the torsional potential has a broad minimum near the D3h (for DABCO) and C3V (for ABCO) conformations.