By using Fourier transform infrared spectroscopy (FTIR) we have witnessed the sequential steps of surface diffusion, weak chemical bonding, and decomposition of dimethyl methylphosphonate (DMMP) on TiO2 powder. At temperature lower than similar to 160 K, DMMP condenses as an ice layer on the outer surface of the TiO2 sample. Tn the temperature range 160-200 K, diffusion into the TiO2 interior occurs and hydrogen bonding of DMMP to isolated TiOH groups is observed. In addition, bonding to Lewis acid sites occurs. Above 214 K, cleavage of P-OCH3 groups takes place, with the production of Ti-OCH3 surface species and this is accompanied by the consumption of surface hydroxyl groups. A reduction of P-O bond order then occurs as adsorbed phosphonate species are formed.