High sensitivity temperature-programmed desorption mass spectrometry (TPDMS) was employed in order to investigate the desorption kinetics of CCl 4 from thin (∼500 ML (ML: monolayer)) amorphous D 2 O ice films. TPDMS experiments demonstrate that at low coverages CCl 4 is trapped in the pores near the surface of microscopically rough ice. Three distinct desorption features, µ-, δ-, and -CCl 4 , consistent with the release of trapped CCl 4 were observed. The µ-, δ-, and -CCl 4 desorption yields demonstrate high sensitivity to the temperature and rate of ice film deposition. We interpret these results as evidence of the existence of three metastable forms of microporous amorphous ice, I µ , I δ , and I . Measurements of the relative desorption yields from CCl 4 species trapped at the surface of ice films prepared at different temperatures and deposition rates were used in order to estimate the barriers to the diffusion of D 2 O on the surface of I δ (E Dδ ) and I (E D ). The values obtained were E Dδ ) 5 ( 1 kcal mol -1 and E D ) 9 ( 2 kcal mol -1 . We suggest that I µ , I δ , and I can be characterized respectively by the relative abundances of two-, three-, and four-coordinated D 2 O molecules at the ice surface. A proposed phase diagram for thin D 2 O ice films is presented.