Optical and dielectric functions of liquid hexamethylphosphoric triamide between 2 and 25 eV

The reflectance of liquid hexamethylphosphoric triamide has been determined between 2 and 9 eV by the semicylinder method and between 10 and 25 eV by the double ionization chamber method. Kramers-Kronig analysis of the data gave the optical and dielectric functions, the energy loss functions, and the effective number of electrons, all as a function of photon energy. Structure in the absorption spectrum and the imaginary part of the complex dielectric function at 7.5 and 11.5 eV are associated with excitation of π and σ electrons, respectively. The σ→σ* excitation is shifted in the energy loss function −Im(1/ε) to 21 eV, indicating an appreciable degree of collective behavior. Of the total 68 valence electrons, the number of electrons taking part in optical processes and energy loss processes increases to 38 and 25, respectively, at 25 eV.