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

Abstract

The emission spectrum of the molecule OH (A 2Σ→X 2Π, 0–0) during a high-voltage, bi-directional pulsed corona discharge consisting of a gas mixture of N 2 and H 2O 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 N 2 (C, v′) have also been determined. Due to the difficulty of determining the exact overlapping spectral line shape function of the OH (A 2Σ→X 2Π, 0–0) and the Δ v=+1 vibrational transition band of N 2 (C 3Π u→B 3Π g), a practicable Gaussian form is used for calculating the emission intensity of OH (A 2Σ→X 2Π, 0-0) and the Δ v=+1 vibrational transition band of N 2 (C 3Π u→B 3Π g). The emission intensity of OH (A 2Σ→X 2Π, 0–0) has been evaluated with a satisfactory accuracy by subtracting the emission intensity of the Δ v=+1 vibrational transition band of N 2 (C 3Π u→B 3Π g) from the overlapping spectra. The relative population of OH (A 2Σ) has been obtained by the emission intensity of OH (A 2Σ→X 2Π, 0–0) and Einstein's transition probability. The influences of peak voltage, pulse repetition rate and O 2 flow rate on the relative population of OH (A 2Σ) radicals have also been investigated. We found that the relative population of OH (A 2Σ) rises with an increase in both the peak applied voltage and the pulse repetition rate. When oxygen is added to an N 2 and H 2O gas mixture, the relative population of OH (A 2Σ) radicals decreases exponentially with an increase in added oxygen. The main physicochemical processes involved are also discussed in this paper.