The kinetics and the reaction patterns of the HO3+ and H2O3+ ions toward a variety of inorganic and organic substrates have been investigated by using Fourier-transform ion cyclotron resonance (FT-ICR) spectrometry. The thermochemistry of the HO3+ and H2O3+ ions is evaluated from correlations between their proton transfer (PT) efficiencies and the proton affinity (PA) of the selected substrates. Similarly, thermochemical data on HO3 and H2O3 species are inferred from a comparison between the electron transfer (PT) efficiencies of their cationic counterparts and the standard ionization energies (IE) of the substrates. Thus, in striking contrast with most literature theoretical and empirical estimates, an experimental value of -1 +/- 5 kcal mol(-1) is obtained for the standard heat of formation of HO3. Accordingly, ground-state HO3 ((2)A) is thermochemically stable toward dissociation to HO((2) Pi) and O-2((3) Sigma(g)(-)), and therefore, its existence as a true intermediate in key ionic reactions occurring in the upper atmosphere cannot be excluded. The standard formation enthalpy of H2O3+ (198 +/- 5 kcal mol(-1)) is evaluated by two independent approaches, while that of the HOOOH neutral molecule is estimated as less than or equal to-26 kcal mol(-1). The HO3+ ion displays a variegated chemistry. Depending of the nature of the reactive centers of the neutral substrate, the HO3+ ion may react as a Bronsted or a Lewis acid, as an oxenium ion or an oxygen-centered free radical. When all these pathways are thermochemically precluded, as with CO, a ligand swiching process takes place in HO3+ to give the CHO2+ ion, which may promote a three-step acid-catalyzed cycle for the O-3 oxidation of CO to CO2 and O-2. Likewise, the less reactive H2O3+ ion undergoes ligand swiching by water.