Abstract
The multiphoton ionization (MPI) and two-photon fluorescence excitation (TPFE) spectra of triethylenediamine (DABCO) are obtained and analyzed. A low-lying state (0–0 at 35 795 cm−1) is observed as a two-photon resonance in the four photon ionization spectrum and also in the TPFE spectrum. Circular vs linear laser polarization studies give an A′1 symmetry for this state. The state results from a 3s (+) ←n (+) orbital promotion. The vibrational progressions and sequences observed are also analyzed. The lifetime of the fluorescence resulting from two-photon 1A′1←1A′1 excitation compares well with the lifetime observed upon one-photon ?←? excitation,suggesting that the 1A′1 state is the emitting state. This 1A′1← 1A′1 one photon forbidden, two-photon allowed, transition is most probably responsible for the very weak long wavelength absorption reported in previous conventional spectroscopic studies. The MPI spectra and laser polarization characteristics of the strong (0–0 at 39 825 cm−1) transition of DABCO are also investigated. The transition is found to be both one- and two-photon allowed and is assigned as 1E″[3px,y (+)]←1A1[n (+)].
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