A comparative examination of ejection dynamics in the UV irradiation of CH3I and CD3I films (lambda = 248 nm) is presented. Deuteration is shown to result in an increase of the ablation threshold and in a decrease of the ejection efficiencies, while the effect on the translational distributions is rather weak and due to the difference in the desorbing amount. These effects are shown to be largely due to the change in the heat capacity of the system. Independently of the specific conclusion, the examination of deuterium substitution effects in UV ablation of molecular solids provides a potentially interesting method for assessing the nature of the photophysical/chemical processes of the phenomenon. (C) 2002 Published by Elsevier Science B.V.