Heterogeneous quenching of O2(1Deltag) molecules in H2:O2mixtures

Quenching of O 2 ( 1 g ) molecules both in the gas phase and on a reactor surface has been investigated in binary mixtures of hydrogen and oxygen by using the fast-flow quartz reactor and infrared emission spectroscopy. Rate constants of the O 2 ( 1 g ) deactivation by H 2 and O 2 at room temperature have been determined to be (1.5±0.5) 10 -18 cm 3 s -1 and (1.6±0.2) 10 -18 cm 3 s -1 , respectively. Heterogeneous quenching of O 2 ( 1 g ) on quartz walls has been studied both in pure oxygen and in H 2 :O 2 mixtures. A model of O 2 ( 1 g ) heterogeneous quenching in binary mixtures has been developed and has allowed us to describe all observed features of singlet oxygen kinetics. Active surface complexes formed by `chemisorbed' atomic oxygen and `physadsorbed' molecules of O 2 and H 2 are assumed to be responsible for the O 2 ( 1 g ) heterogeneous deactivation. It has been shown that the higher rate of O 2 ( 1 g ) quenching in pure oxygen is connected with a quasi-resonant transfer of the O 2 ( 1 g ) electronic excitation to physadsorbed oxygen molecules. The observed effect of the wall passivation by hydrogen is conditioned both by the absence of the similar resonance in the hydrogen surface complex and by the higher bond energy of H 2 in this complex. Bond energies of O 2 (3750±450 K) and H 2 (4050±450 K) in the surface complexes have been determined from the model parameters by fitting calculations to experimental results.