The adsorption of PMeCl(2) and of mixtures of PMeCl(2) and PCl3 on silica have been studied using infrared spectroscopy and P-31 solid-state NMR. PMeCl(2) gives a single phosphorus containing product (A) as a result of a reaction with surface SiOH groups, SiOP=O(H,Me); HCl and surface SiCl are byproducts of the reaction. A reaction mechanism has been devised. The rate of reaction is slow and high pressures of reactant (10 to 80 Torr) are required. Commercially available PMeCl(2) samples are usually contaminated with PCl3 at the 2 to 5 mol % level. At the pressures needed to effect chemisorption of PMeCl(2), the contaminant PCl3 has a significant influence on the course of the reaction. The major feature with such low levels of PCl3 as an impurity is the conversion of A to a second species B, (SiO)(2)P=O(H), with minor amounts of SiOP=O(H,OH). A plausible sequence of reaction steps leading to this product has been elaborated, but the chemistry is complex.