Optical properties of some aromatic liquids in the vacuum ultraviolet

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Abstract
The optical properties of benzene, pyridine, quinoline, and 2‐ethylnaphthalene in the liquid state have been studied for photon energies from 2 to 10.6 eV. For each liquid the extinction coefficient k has been obtained from transmission measurements, and self‐consistent values of the refractive index n calculated over the experimental energy range by a Kramers‐Kronig analysis. The calculated absorption cross sections per liquid molecule have been compared with the corresponding absorption cross sections per vapor molecule, where the vapor data have been obtained from the literature. The absorption cross section spectra for liquid and vapor are very similar in the energy region studied, such that the observed absorption can be attributed to the same electronic excitations in both phases. In addition, evidence of collective excitations of electrons, not seen in the vapor state, is seen in all four liquids.