Weighted average IR spectra of CO3 center dot-center dot nH(2)O (n = 1-6) clusters are reported and compared with those of CO32-center dot nH(2)O (n = 1-6) clusters based on quantum chemical calculations. Simulated annealing combined with the Monte Carlo sampling method is also applied to locate the global minimum energy structure. It is observed that hydrated clusters of CO3 center dot- ion having cyclic water networks are the most stable structure in each size of hydrated cluster. IR bands at the lower side of the O-H stretching region of water correspond to single/double hydrogen bonding interaction, and those in the higher side correspond to inter water hydrogen bonding for the lower clusters (n = 2-3). For the tetrahydrated cluster of CO3 center dot- ion, a complete crossover of the IR spectra in the O-H stretching region occurred. Cyclic water networks having three or four solvent water molecules are characterized by strong peaks at 3550 and 3450 cm(-1). In the case of CO3 center dot-center dot nH(2)O clusters, O-H stretching bands of all of the solvent water molecules are above 3100 cm(-1) in contrast to that of CO32-center dot nH(2)O clusters showing distinctive IR signature. This suggests that size selected hydrated clusters of CO3 center dot- and CO32- ions can easily be distinguished on the basis of their IR spectra.