Discussion
This simulation shows photoionization of the 5a1 (C–I σ-bonding electron) in CF3I, but now with a fully random light polarization direction assumed. Consequently, both electric dipole allowed channels, 5a1 → ka1 and 5a1 → ke, are excited. At low energies the ionization is dominated by a broad intense ke shape resonance centred at 2.5 eV.
At energies just above the shape resonance the predicted MF-PAD has been partially confirmed by experiments that effectively fix the molecular orientation in a gas phase sample from the correlation between electron and fragment ion recoil directions — see P. Downie & I. Powis, Phys. Rev. Lett., 82 (1999), 2864; J. Chem. Phys., 111 (1999), 4535).
Once again it may be noted how richly structured the MF-PAD is at any energy compared the maximum cos2θ form expected for lab frame PADs; this is because of the smearing out and loss of detail caused by averaging the distribution over all possible molecular orientations in the lab frame.
The Animation
This animation shows the results of photoionization calculations made using the CMS-Xα method. The molecule-frame photoelectron angular distribution (MF-PAD) prediction that is obtained appears here in a three dimensional representation indicating the relative probability of electron ejection in a given direction specified in the molecular coordinate frame. The orientation of the molecule can be identified from the transluscent atomic spheres; as the electron energy is scanned from threshold up to around 20 eV the molecule is allowed to rotate around its axis to help reveal the 3-D characteristics of the MF-PAD. An inset panel shows the total (integrated) photoionization with a marker point that moves along the cross-section curve as the energy is scanned.
