Experimental results demonstrate O 2 a 1 Δ g (υ 0) formation by catalytic O-atom surface recombination in a room-temperature fused-quartz flow-tube reactor. Resonance-enhanced multiphoton ionization is used to detect O 2 a 1 Δ g (υ 0) 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 O 2 a 1 Δ g (υ 0) resonanceenhanced multiphoton ionization signals. Partial pressures of O 2 a 1 Δ g (υ 0) in the range of 2.9 to 14 μtorr are measured in the ionization cell for O-atom partial pressures of 1.4-2.9 mtorr atomic oxygen introduced at the titration port. O 2 a 1 Δ g (υ 1) could not be detected; an upper limit for the O 2 a 1 Δ g (υ 1) partial pressure is one-fifth of the O 2 a 1 Δ g (υ 0) partial pressure. A simple chemical kinetics model demonstrates that measured O 2 a 1 Δ g 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 O 2 a 1 Δ g on the tube walls must be included to satisfactorily model the experimentally observed pressures and trends. Modeling results also suggest that the O 2 a 1 Δ g surface production yield is 10% or more.
Nomenclatureaverage thermal speed; 8RT∕πM p , m · s −1 γ = reaction efficiency χ = mole fraction Subscripts ac = absorption cell ave = average cal = calibration d = dissociation ep = endpoint ft = flow tube in = input J = rotational level N = atomic nitrogen NO = nitric oxide N2 = molecular nitrogen O = atomic oxygen O2= molecular oxygen O2Δ = singlet delta molecular oxygen O3 = ozone rc = resonance-enhanced multiphoton ionization cell tp = titration port υ = vibrational level w = wall