Singlet Molecular Oxygen Formation by O-Atom Recombination on Fused-Quartz Surfaces

Abstract

Experimental results demonstrate () formation by catalytic O-atom surface recombination in a room-temperature fused-quartz flow-tube reactor. Resonance-enhanced multiphoton ionization is used to detect () downstream of a nitrogen discharge flow titrated with nitric oxide to introduce oxygen atoms. A calibration procedure based on ozone photodissociation is developed to quantify () resonance-enhanced multiphoton ionization signals. Partial pressures of () in the range of 2.9 to are measured in the ionization cell for O-atom partial pressures of 1.4–2.9 mtorr atomic oxygen introduced at the titration port. () could not be detected; an upper limit for the () partial pressure is one-fifth of the () partial pressure. A simple chemical kinetics model demonstrates that measured pressures cannot be explained by gas-phase chemistry alone and must involve O atoms participating in surface reactions. It is found that collisional deactivation of on the tube walls must be included to satisfactorily model the experimentally observed pressures and trends. Modeling results also suggest that the surface production yield is 10% or more.