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

TL;DR

This study uses VUV photoelectron spectroscopy to analyze DABCO, revealing precise ionization energy, vibrational modes, and how vibrational excitation affects photoelectron angular distribution due to Rydberg state interactions.

Contribution

First detailed VUV photoelectron study of DABCO, identifying vibrational modes and their influence on angular distributions with implications for molecular scattering mechanisms.

Findings

Accurate ionization energy of DABCO at 7.199 eV.

Resolved vibrational progressions at 847 and 1257 cm⁻¹.

Vibrational excitation influences photoelectron angular distribution.

Abstract

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 $7.199\pm0.006$~eV. Two vibrational progressions of DABCO cation ground state are resolved at $847~\text{cm}^{-1}\pm27~\text{cm}^{-1}$ and $1257~\text{cm}^{-1}\pm67~\text{cm}^{-1}$, which we assign to modes of $e'$ 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.