The optimum deposition condition in liquid source metalorganic chemical vapor deposition (MOCVD) of (Ba,Sr)TiO3 films was significantly dependent on the chemical structures of titanium source molecules. To clarify the origin of this dependence, we investigated the reaction mechanisms of the individual titanium sources by in situ infrared absorption spectroscopy. A systematic study on the reaction mechanism of MOCVD source molecules was carried out using a novel titanium source molecule, Ti(MPD)(DPM)(2) [methylpentanediolbis(dipivaloylmethanato)titanium]. The obtained data on Ti(MPD)(DPM)(2) were discussed by comparing with those on the conventional titanium CVD sources such as Ti(t-BuO)(2)(DPM)(2) [bis (tert-butoxy)bis(dipivaloylmethanato)titanium] and Ti(i-PrO)(2)(DPM)(2) [bis(iso-propoxy)bis(dipivaloylmethanato)titanium]. Ti(MPD) (DPM)(2) is about as thermally stable as Ti(t-BuO)(2)(DPM)(2) and more stable than Ti(i-PrO)(2)(DPM)(2). The thermal stability of the organometaltic molecules as a whole is determined by the stability of the moieties other than the DPM ligands. The addition of O-2 have little influence on the temperature dependence of the infrared absorption of Ti(MPD)(DPM)(2) in the gas phase under the actual CVD conditions. The competition between thermal decomposition and oxidation of titanium sources is also sensitive to the structures of their ligand groups other than DPM groups. (C) 2004 The Electrochemical Society.