Reactions of titanium dioxide with acetylene molecules have been studied using matrix isolation infrared absorption spectroscopy. The titanium dioxide molecules were prepared by the reactions of laser-ablated titanium atoms with dioxygen. In solid argon, titanium dioxide molecule reacted with acetylene to form the TiO2-C2H2 complex spontaneously on annealing. The complex underwent photochemical rearrangement to the OTi(OH)CCH and H2Ti(CO)(2) isomers upon UV-visible photolysis. The product absorptions were identified by isotopic substitutions and density functional calculations of isotopic frequencies.