Behaviour of atomic oxygen in a pulsed dielectric barrier discharge measured by laser-induced fluorescence

Atomic oxygen is measured in a pulsed dielectric barrier discharge (DBD) using two-photon absorption laser-induced fluorescence (TALIF). The ground-level atomic oxygen is excited to the 3p 3P state by two-photon absorption at 226 nm. Negative (-40 kV) or positive (+30 kV) pulsed DBD occurs in an O2-N2 mixture at atmospheric pressure. The pulse width of the DBD current is approximately 50 ns. The TALIF experiment shows that the decay rate of atomic oxygen increases linearly with O2 concentration. This result proves that atomic oxygen decays mainly by the third-body reaction, O + O2 + M → O3 + M. The rate coefficient of the third-body reaction is estimated to be 2.2 x 10-34 cm6 s-1 in the negative DBD and 0.89 x 10-34 cm6 s-1 in the positive DBD. It is shown that the decay rate of atomic oxygen increases linearly with humidity. This can explain the well-known fact that ozone production in DBD is suppressed by increasing humidity