A general sticking coefficient theory for neutral and photochemically excited molecules

This paper discusses a general sticking coefficient theory for both neutral molecules (no photochemical reaction effects) and photochemically excited molecules in a solar vacuum ultraviolet (VUV) radiation environment. For neutral-molecule problems, the theory is based on the classical adsorption kinetics concept for either a single-component or multi-component gas on a surface with a constant incident flux. The theory has been verified satisfactorily with available DC-704 test data For photochemically induced adsorption problems, a sticking coefficient model modified from that in the literature is proposed. This model asserts that photochemical reactions can take place only if the neutral-molecule residence time is longer than the photoexcitation dwell time (or whether the photoexcitation rate is higher than the thermal desorption rate). The total (effective) sticking coefficient is the sum of the neutral-molecule sticking coefficient and the photoexcited-molecule sticking coefficient. The photochemically induced deposition enhancement predicted by the present theory shows reasonable agreement with data presented in the literature.