The adsorption of zirconium nitrate [Zr(NO3)(4), ZN] on thin films of polycrystalline zirconia (ZrO2) was investigated with temperature-programmed reaction mass spectrometry (TPR) and X-ray photoelectron spectroscopy (XPS). TPR measurements demonstrate that adsorbed ZN undergoes competitive desorption and reaction near 340 K. The reaction is the first in a series of steps that ultimately leads to ZrO2 formation. Several gas-phase products are formed as a result of ZN decomposition, including NO, NO3, and O-2. The gas-phase products evolve from two temperature envelopes centered at similar to350 and similar to400 K, with the O-2 envelopes at somewhat higher temperature than the NO and NO3 envelopes. Partitioning between the desorption and decomposition pathways is a function of the heating rate, beta, during TPD, with the ZN desorption fraction varying between 0.05 at beta = 1 K s(-1) and 0.4 at beta 5 8 K s(-1). The XPS measurements reveal that the zirconium oxidation state is constant at +4 during the decomposition sequence. However, the identities of the gas-phase products suggest that the NO3 ligands undergo oxidation-reduction chemistry during decomposition. On the basis of the TPR and XPS measurements, it is proposed that adsorbed peroxides of formula Zr(NO3)(2)(O-2) and ZrO(O-2) are intermediates on the decomposition pathway. Both peroxides contain states of oxygen that are oxidized relative to oxygen in ZN.