CF3I MF-PAD Animation || Polarization

Powis Group

MF-PAD for CF3I Photoionization

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Discussion

The simulations here concern photoionization of the 5a1 C–I σ-bonding electron in CF3I. With the polarization set parallel to the molecular axis, selection rules dictate that the photoelectron enters a similarly symmetric ka1 continuum function.

Notice how highly structured the PAD in this fixed molecular axis reference frame is, varying smoothly, but very substantially, over most of the energy range spanned. Classical reasoning might readily suggest that an electron would find it easier to escape from one end of a molecule than the other, but the detail observed here can only arise through a full quantum scattering treatment of the photoionization dynamics.

This photoionization may be compared with the analogous 5a1ka1 ionization of CF3Cl that appears elsewhere. The shape resonant enhancement of the cross-section, visible at 3.5 eV, is, however, much less prominent in this instance. Nevertheless the rate of change in the MF-PAD still accelerates in the region of this weaker resonance.

It may again be noted how richly structured (with many spherical harmonics) the MF-PAD is at any energy compared to 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. Although undoubtedly a more challenging experiment, this level of additional detail indicates how much more useful fixed-molecule photoionization studies may prove.

The Animation

This animation shows calculated molecule-frame photoelectron angular distributions (MF-PADs) made, using the CMS-Xα method, for a photoionization of CF3I.

The MF-PAD appears 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 cross-section curve with a marker point that moves along the cross-section curve as the energy is scanned.