Knowing the tautomeric form of malonic acid (MA) in concentrated particles is critical to understanding its effect on the atmosphere. Energies and vibrational modes of hydrated MA particles were calculated using density functional theory (DFT) at the B3LYP/6-31G(d,p) level and the effective fragment potential (EFP) method. Visualization of the keto and enol isomer vibrational modes enabled the assignment of keto isomer peaks in. the 1710-1750 cm(-1) range, and previously unidentified experimental IR peaks in the 1690-1710 cm(-1) can now be attributed to the enol isomer. Comparison of calculated spectra of pure hydrated enol or keto isomers:confirm recent experimental evidence; presented by Ghorai et al. (I. Phys. Chem. A 2011, 115, 4373-4380) of a shift in the keto-enol tautomer equilibrium when MA exists as concentrated particles.