The adsorption, thermal stability, and photochemical reactions of N(C2H5)(3) on powdered TiO2 have been studied by Fourier transform infrared spectroscopy (FTIR). N(C2H5)(3) molecules are adsorbed molecularly on TiO2 at 35 degreesC and can be removed from the surface at 300 degreesC in a vacuum. In the presence of O-2, N(C2H5)(3) starts to decompose on TiO2 at a temperature of similar to215 degreesC. N(C2H5)(3) on TiO2 is desorbed from the surface upon photoirradiation. In the presence of O-2, the photodesorption process is suppressed and photoreactions of N(C2H5)(3) are promoted. CO2(g), H2O(a), NCO(a), HCOO(a), CH3COO(a), and surface species containing NHx, Cdouble bondO, C-N, or C-N-C groups are detected during N(C2H5)(3) photodecomposition on TiO2. As H2O is added to the photoreaction system of N(C2H5)(3) on TiO2 in O-2, the amounts of NCO(a) and NHx, detected during photoirradiation decrease, but with appearance of Cdouble bondN groups. Most importantly, it is found that H2O participates in the HCOO(a) and CH3COO(a) formation.