Pulse Radiolysis Studies. XX. Kinetics of Some Addition Reactions of Gaseous Hydrogen Atoms by Fast Lyman-α Absorption Spectrophotometry

The pulse radiolysis technique combined with fast Lyman-α absorption spectrophotometry, has been used to study the kinetics of several addition reactions of gaseous hydrogen atoms. The following absolute rate constants, at 298°K, have been obtained: H+O2+Ar=HO2+Ar, (5.9 ± 0.7) × 109M−2·sec−1, H+CO+H2=HCO+H2, (4.0 ± 0.6) × 107M−2·sec−1, H+CO+Ar=HCO+Ar, (2.6 ± 0.4) × 107M−2·sec−1, H+NO+H2=HNO+H2, (1.4 ± 0.2) × 1010M−2·sec−1. These results, and our earlier value for k1 with H2 as third body, give values of k1H2 / k1Ar = 2.9 and k2H2 / k2Ar = 1.5 for the relative third-body efficiencies of hydrogen and argon. The high-pressure limiting rate constant for H-atom addition to ethylene, obtained directly in the high-pressure region, was found to be H+C2H4=C2H5*, (5.5 ± 0.5) × 108M−1·sec−1, with both H2 and Ar as third body.