Reactions during the atomic layer deposition (ALD) process of ZrO2 from CP2Zr(CH3)2 and deuterated water as precursors were studied with a quadrupole mass spectrometer (QMS) at 210-440 degrees C. The detected reaction byproducts were CpD (m/z = 67) and CH3D (m/z = 17). Almost all (90%) of the CH3 ligands were released during the CP2Zr(CH3)(2) precursor pulse because of exchange reactions with the OD-terminated surface, and the rest, during the D2O pulse. About 40% of the CpD was released during the metal precursor pulse, and 60%, during the D2O pulse. ALD-type self-limiting growth was confirmed from 210 to 400 degrees C. However, below 300 degrees C the growth rate was low. Precursor decomposition affected the film growth mechanism at temperatures exceeding 400 degrees C.