DIAGNOSTICS AND MODELING OF RF DISCHARGE DISSOCIATION IN N2O

We measured the RF discharge dissociation of N2O in a parallel-plate reactor by downstream mass spectrometry. We used a wide range of gas flows and powers at 10 KHz and 13.56 MHz. The results show that the mass 44 signal (N2O+), which is a measure of the amount of undissociated N2O, is a function of the discharge input energy per N2O molecule (eV/N2O). The amount of dissociation increases as eV/N2O increases. The primary downstream products are N2, O2, and NO. The densities of these product species also depend only on eV/N2O. With the same eV/N2O value, the dissociation rate is similar at both frequencies. A plug flow, rate equation model of the discharge was used to predict the experimental dissociation rates. A dc Monte Carlo simulation was used to calculate rate coefficients for electron-impact neutral dissociation, ionization, and dissociative ionization. The E/n value assumed in the Monte Carlo calculation was the time- and space-averaged value of E/n in the discharge. Published vibrational and electronic excitation cross sections were used, together with an estimated momentum transfer cross sections and measured N2O+ and dissociative ionization cross sections. The neutral dissociation rate coefficient was estimated by assuming that the lowest electronic state of N2O is dissociative. The rate equation model also includes reactions among the dissociation products of N2O and species which are synthesized in the discharge, as well as neutral and electron-ion recombination at the electrodes. Published rate coefficients were used for the gas phase heavy-particle reactions. The ion recombination rate coefficients were estimated from measured ion mobilities. The rates for the neutral recombination reactions were estimated by comparing predicted and measured results. The predicted values of the downstream product densities versus eV/N2O agree with the experimental results. The model predictions identify the major reaction pathways and the sensitivities of the results to the rate coefficient values used.