The dependence of the near-edge X-ray absorption fine structure (NEXAFS) spectrum of molecules on the photon electric field direction is investigated by means of first-principles simulations based on density functional theory with the transition-potential approach. In addition to the well-known dependence of the NEXAFS resonances on the orientation of the electric field with respect to the molecular plane, we demonstrate that for planar molecules with sufficient in-plane anisotropy such as pentacene a dichroic effect is found with a splitting of the sigma* resonance as a function of the azimuthal orientation of the photon electric field in the molecular plane. The sigma* splitting is investigated as a function of the length of acenes and closely related molecules. A proper assignment of such spectral features guided by theory together with variable polarization experiments may allow one to completely determine the orientation of molecules at interfaces.
Azimuthal Dichroism in Near-Edge X-ray Absorption Fine Structure Spectra of Planar Molecules
Luca Floreano;
2013
Abstract
The dependence of the near-edge X-ray absorption fine structure (NEXAFS) spectrum of molecules on the photon electric field direction is investigated by means of first-principles simulations based on density functional theory with the transition-potential approach. In addition to the well-known dependence of the NEXAFS resonances on the orientation of the electric field with respect to the molecular plane, we demonstrate that for planar molecules with sufficient in-plane anisotropy such as pentacene a dichroic effect is found with a splitting of the sigma* resonance as a function of the azimuthal orientation of the photon electric field in the molecular plane. The sigma* splitting is investigated as a function of the length of acenes and closely related molecules. A proper assignment of such spectral features guided by theory together with variable polarization experiments may allow one to completely determine the orientation of molecules at interfaces.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.