Temperature-Dependent Ultraviolet Photoemission Linewidths of Molecular Solids: Isopropyl Benzene

Abstract

The temperature ($T$) dependence of the width of the first ionization potential of condensed films of isopropyl benzene has been measured by ultraviolet photoelectron spectroscopy with use of synchrotron radiation. Over the range $15°\mathrm{K}<~T<~150°\mathrm{K}$, the linewidth exhibits the form ${\delta }^2\mathrm{}\left(T\right)={\delta }^2\mathrm{}\left(0\right)+c^{2}T$, where $c=4.4\mathrm{} (\pm 0.8)\times {10}^{-2\mathrm{}}$ eV/${\left(\mathrm{°}\mathrm{K}\right)}^{\mathrm{½}}$. This $T$ dependence originates from the interaction of the photogenerated localized molecular hole states with low-energy vibrational modes of the film.