Momentum dependence of π–π∗ excitations of benzene rings in condensed phases

What is it about?

Inelastic X-ray scattering (IXS) spectra for the pi-pi* excitation of benzene, toluene, polystyrene, and benzene-hexane solutions have been measured at medium momentum transfers (q), 0.35 less than or equal to q less than or equal to 1.5 Angstrom (-1). IXS profiles of these substances closely resemble each other. The pi-pi* peak of the pure substances shows a negative q-dispersion (~0.5 eV), while diluted benzene does not. For benzene, the loss function and the real (e1) as well as the imaginary (e2) parts of the dielectric function were deduced. It is shown that the pi-pi* excitation in liquids is well-localized and the q-dispersion can be interpreted by changes of the shielding factor. The properties of the loss function for molecular condensates are discussed.

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