We have investigated the thermochemistry and ion energetics of the oxybenzone (2-hydroxy-4-methoxy-benzophenone, C14H12O 3, 1H) molecule. The following parameters have been determined for this species: gas-phase enthalpy for the of neutral molecule at 298.15K, (ΔfHm0(g) = -303.5 ± 5.1 kJ·mol-1). the intrinsic (gas-phase) acidity (GA(1H) = 1402.1 ± 8.4 kJ·mol-1), enthalpy of formation for the oxybenzone anion (Δf Hm0(1-,g) = -402.3 ± 9.8 kJ·mol-1). We also have obtained the enthalpy of formation of, 4-hydroxy-4′-methoxybenzophenone (ΔfHm0(g) = -275.4 ±10 kJ·mol-1) and 3-methoxyphenol anion (ΔfH m0(C7H7O2-,g) = -317.7 ± 8.7 kJ·mol-1). A reliable experimental estimation of enthalpy related to intramolecular hydrogen bonding in oxybenzone has also been obtained (30.1 ±6.3 kJ·mol-1) and compared with our theoretical calculations at the B3LYP/6-311++G** level of theory, by means of an isodesmic reaction scheme. In addition, heat capacities, temperature, and enthalpy of fusion have been determined for this molecule by differential scanning calorimetry. © 2008 American Chemical Society.