Low-frequency large-amplitude vibrations of julolidine in the S0 and S1 states

The vibrational modes of julolidine in the ground- and the first-excited states have been investigated by laser-induced fluorescence (LIF), multiphoton ionization (MPI) and dispersed emission spectroscopy. In the observed LIF excitation spectrum the mode 140 cm−1 appears and is assigned to the N-inversion mode of the S1 state which gets coupled with the ring puckering modes of the fused saturated six-membered ring. A progression of 148 cm−1 intervals appears in the dispersed emission spectra, which on the basis of semi-empirical calculations has been identified as the N-inversion mode of the ground state.