Diagnosis of OH radical by optical emission spectroscopy in a wire-plate bi-directional pulsed corona discharge

The emission spectrum of the molecule OH (A2Σ→X2Π, 0–0) during a high-voltage, bi-directional pulsed corona discharge consisting of a gas mixture of N2 and H2O in a wire-plate reactor has been successfully recorded under severe electromagnetic interference at atmospheric pressure. The relative vibrational populations and the vibrational temperature of N2 (C, v′) have also been determined. Due to the difficulty of determining the exact overlapping spectral line shape function of the OH (A2Σ→X2Π, 0–0) and the Δv=+1 vibrational transition band of N2 (C3Πu→B3Πg), a practicable Gaussian form is used for calculating the emission intensity of OH (A2Σ→X2Π, 0-0) and the Δv=+1 vibrational transition band of N2 (C3Πu→B3Πg). The emission intensity of OH (A2Σ→X2Π, 0–0) has been evaluated with a satisfactory accuracy by subtracting the emission intensity of the Δv=+1 vibrational transition band of N2 (C3Πu→B3Πg) from the overlapping spectra. The relative population of OH (A2Σ) has been obtained by the emission intensity of OH (A2Σ→X2Π, 0–0) and Einstein's transition probability. The influences of peak voltage, pulse repetition rate and O2 flow rate on the relative population of OH (A2Σ) radicals have also been investigated. We found that the relative population of OH (A2Σ) rises with an increase in both the peak applied voltage and the pulse repetition rate. When oxygen is added to an N2 and H2O gas mixture, the relative population of OH (A2Σ) radicals decreases exponentially with an increase in added oxygen. The main physicochemical processes involved are also discussed in this paper.