We report structural and kinetic studies of the reactions of hydride species in Si thin films with atomic deuterium (Dat). Infrared (IR) spectroscopy is used to obtain Si-H bonding information, and direct recoiling methods are used to measure reaction rates. Two kinds of films are prepared by filament-assisted growth from Si2H6 and are characterized by IR spectroscopy. A film containing only monohydride hydrogen is grown at 200 °C, and a polymer containing tri-, di-, and monohydride is grown at -110°C. Rates of H abstraction by Dat, and of Dat insertion into Si-Si bonds, are reported. The abstraction rate of H by Dat in both films is similar to the abstraction rate on H-terminated crystal Si surfaces. The insertion rate into Si-Si bonds in both films is about one-tenth the rate of abstraction. A qualitative study of the etching reaction of Dat with the polymeric film is reported, and a strong temperature dependence is observed.