Department of Physics and Astronomy: Publications and Other Research
Date of this Version
2009
Citation
Published in Physical Chemistry Chemical Physics 11 (2009), pp 8448–8455
DOI: 10.1039/b908770b
Abstract
The temporary anion states of gas-phase trans-azobenzene are characterized by means of electron transmission spectroscopy (ETS) in the 0–6 eV range. The measured energies of vertical electron attachment are compared with the energies of the π* virtual orbitals of the neutral molecule supplied by HF (at MP2 optimized geometries) and B3LYP calculations. The calculated energies, scaled with empirical equations, reproduce quantitatively the energies of the corresponding spectral features and predict a positive vertical electron affinity of 0.83 eV.
The total anion current at the walls of the collision chamber and the mass-selected molecular anion current are also reported as a function of the impact electron energy. In agreement with previous data, long-lived (>1 μs) parent molecular anions are detected at zero eV and near 1 eV. The close similarity of the electron transmission spectrum with the derivatives with respect to energy of the anion currents suggests strongly that shape resonances produced by electron capture into empty π* orbitals are the initial step in formation of the long lived molecular anions. This appears to rule out mechanisms in which direct formation of core-excited anion states are invoked. However, according to DFT calculations, conversion of the shape resonances around 1 eV to longer-lived σ–π* core-excited doublet anion states is possible on energetic grounds
Comments
Physical Chemistry Chemical Physics is copyright © 2009 the Royal Society of Chemistry. Used by permission.