HEAT OF FORMATION OF HO2 - A DIRECT DETERMINATION FROM GUIDED ION-BEAM STUDIES OF O-2+(2-PI-G,V=0)+CH4

The heat of formation of the hydroperoxyl radical, HO2, and the ionization energy of methane, IE(CH4), are measured directly, by using guided ion beam mass spectrometry to study the reaction of O2+(2Πg,v=0) + CH4. The O2+ ions are produced in a flow tube source and are shown to be completely thermalized. The thermodynamic values derived are IE(CH4) = 12.54 ± 0.07 eV, ΔfH298(HO2) = 3.8 ± 1.2 kcal/mol, D298°(H-OO) = 48.3 ± 1.2 kcal/mol, and D298°(H-OOH) = 88.4 ± 1.2 kcal/mol (where the uncertainties represent our 95% confidence limits). The present values are compared to prior experimental and theoretical values. © 1990 American Chemical Society.