The Ultraviolet Photoelectron Spectroscopy of Aliphatic Hydrocarbons and Tetramethylsilane in the Solid State

He I, Ne I, and Ar I ultraviolet photoelectron spectra were measured for solid hexane, 3-methylpentane, 2,2-dimethylbutane, neopentane, tetramethylsilane, cyclohexane, and 1-hexene deposited on a substrate at the temperature of liquid nitrogen. The spectra of all the compounds except hexane showed valence-band features. The threshold ionization potential was 7.6–8.9 eV, with a lowering of the threshold from the gas to the solid phase (polarization energy PS) of 1.2–1.8 eV. These PS values are in reasonable agreement with theoretical model calculations. To clarify the effect of intra- and intermolecular factors on PS, the observed PS values were compared with those of liquid-phase and solid-aromatic hydrocarbons. For compounds in which the bottom of the conduction band lies above the vacuum level, the polarization energy data showed that electrons with energies between these states are also emitted, possibly without any excitation of electrons to the conduction band in the bulk of the solid.