The products of the insertion reaction of Hg(P-3(1)) in the SiH (SiD) bond of h- or d-silane in nitrogen and rare gas matrixes are observed by FTIR spectroscopy. This study has shown that the reaction takes place without activation energy. Disilane molecules are formed from the dimers of parent molecules close to mercury or from the complexes of the insertion products with the parent molecules. In this last case a weak isotopic effect shows that the reaction probably takes place through a small barrier. In the krypton matrix the formation of SiH2 and SiH radicals is observed by a mercury-sensitized two-photon excitation. The SiH3 radical is produced upon annealing. A mixed CH4/SiH4 experiment gives the ratio of the insertion rates in these two molecules.