The mechanism of TiO2 thin film deposition on single crystal TiO2 by chemical vapor deposition (CVD) using tetrakis(isopropoxo)titanium(IV) (TTIP) has been investigated. The structure of the rutile(100) surface has been shown to form a 1 X 3 reconstruction using reflection high-energy electron diffraction. Temperature programmed reaction spectroscopy and molecular beam scattering have been employed to probe the kinetics of the reaction of TTIP and to identify reaction products. The deposition mechanism involves two parallel pathways to form TiO2 : at lower temperatures (500-650 K) propene and isopropanol are formed as products; at higher temperatures (>650 K) propene and water are formed as products in a second pathway that becomes dominant. An activation energy of 57 +/- 8 kJ/mol has been measured for the first pathway. The results for the single crystal surface are compared to earlier work on polycrystalline substrates.