Angle-resolved photoelectron spectroscopy of the DABCO molecule probed with VUV radiation

We report a study of the diazabicyclo[2.2.2]octane (DABCO) molecule photoionized using VUV synchrotron radiation in combination with an ion–electron coincidence spectrometer. We determine accurately the adiabatic ionization energy to $7.199\pm 0.006$~eV. Two vibrational progressions of DABCO cation ground state are resolved at $847{\text{cm}}^{-1}\pm 27{\text{cm}}^{-1}$ and $1257{\text{cm}}^{-1}\pm 67{\text{cm}}^{-1}$, which we assign to modes of $e^{\mathrm{\prime }}$ symmetry. Analysis of the photoelectron angular distribution shows that the anisotropy parameter depends on the vibrational excitation. This dependence of the $\beta$ parameter with the vibrational excitation is attributed to the scattering of the outgoing wavefunction mediated by high-lying Rydberg states.