it is small. If Ear = 0, then D(HaB-BH3) = 38.5 kcal and will be reduced by 2Ear if E,,r # 0. It is reasonable to assume 0 5 Ear 5 2 kcal and thus 34 5 D(HaBBHa) 5 38 kcal. To place this determination in perspective, Figure 11 shows the values of b, expected for critical energies corresponding to D(HaB-BH3) values of 28.4, 35.0, and 59.0 kcal. Our data for the homogeneous reaction are also shown. Additional support for our value of the diborane bond energy is obtained by noting that the magnitude of the inverse isotope effect expected for the homogeneous reaction depends on the critical energy. Figure 12 shows this dependence, and we have indicated the expected isotope effects corresponding to values of D(H3B-BH3) of 28.4, 35.0, and 59.0 kcal. Although the measured isotope effect suffers from considerable scatter, it appears good enough to exclude the high value for D(HaBBHa).If one accepts the hypothesis concerning the surface reaction, a value for D(H3B-BH3) can also be calculated from these data. The activation energy for this reaction is a "high-pressure" value and is slightly lower than the true value due to the weak surface interaction. Once again making the approximation that the reverse reaction has negligible activation energy, a value of D(HaB-BH3) of 36 kcal/mol is obtained.Besides the assumption concerning Ear above there are a number of other sources of error which we have estimated as follows. By comparison with the CHaNC the estimated error in the calculation of the absolute rate is about a factor of 2 in the rate or 1 kcal in EBf. The measurement of the area of the reactor exit orifice is probably good to 20% or 0.5 kcal in Eaf. The uncertainty in temperature gives an error of 0.6 kcal in E, ' and the random error in the measurement of b, yields an error of 0.4 kcal in E,'. We conclude that D(H3B-BHa) is 36 f 3 kcal.The lifetimes of positrons in the oxyacid-water systems, H3P04, HzSO4, HC104, "08, and water, and in the hydrogen compound-water systems, HCl, HF, "3, HzO2, and water, were determined. The short lifetime component ( T I ) , the long lifetime component ( 7 2 ) , and the intensity (12) of the long lifetime component were derived from the composite lifetime data. The connection between changes in 12, the solution composition, and hot radical reactions is discussed. Data are discussed in terms of a proposed oxidation of positronium (Ps) by H+ and of possible chemical reactions leading to compounds of Ps and some estimates of bond energies are made: PsO (2.2 The unknown bond strength of 041 in Clod-is estimated as 3.3 f 0.5 eV. 0.5 eV), PsOH ( <1.5 eV) , PsF (2.9 f 0.5 eV) , and PsCl(2.0 i 0.5 eV).