Efficient Electron-promoted Desorption of Benzene from Water Ice Surfaces

Desorption of benzene (C₆H₆) from solid water surfaces [compact amorphous solid water (c- ASW) and crystalline ice (CI)] during irradiation of ultrathin solid films with low energy (250-300 eV) electrons has been investigated. The observed desorption behaviour is complex but typically two desorption components, with particularly large cross-sections, were present in the observed signal. A fast component, with a cross-section up to 10⁻¹⁵ cm², is attributed to desorption of isolated C₆H₆ molecules that are hydrogen-bonded to small clusters of water (H₂O) molecules on the solid water surface. A slower component, with a cross-section of ca. 10⁻¹⁷ cm², is attributed mainly to desorption from larger C₆H₆ islands on the solid water surface. Possible desorption mechanisms are proposed and astrophysical implications are discussed.