RADIO-FREQUENCY PLASMA DECOMPOSITION OF AMMONIA - A COMPARISON WITH RADIATION-CHEMISTRY USING THE G-VALUE

We have measured G(-NH3) for ammonia vapor passing through a 13.56 MHz , inductively coupled discharge operating within a wide range of press ures (3.5-40 Torr), flow rates (1-3 L/min (STP)), and absorbed power ( 0.2-1.4 kW). Under these conditions, we found values of G(-NH3) lying between 4.2 and 30 molecules/100 eV. By comparison, under similar cond itions, the efficiency of ammonia conversion by a radio frequency, cap acitatively coupled discharge is 6.0-20 molecules/100 eV (Baird, J. K. ; Miller, G. P.; Li, N. J. Appl. Phys. 1990, 68, 3361), while for ioni zing radiation it is 2.7-10 molecules/100 eV (Peterson, D. B. The Radi ation Chemistry of Gaseous Ammonia, Report No. NSRDS-NBS 44, U.S. Depa rtment of Commerce, Washington, DC, 1974). The differences are probabl y due to the specific form assumed by the electron velocity distributi on in each case. The similarities with respect to order of magnitude, however, may have their origin in a common reaction mechanism. Exploit ing this hypothesis, we have derived a formula for G(-NH3) in terms of scattering cross sections, the electron velocity distribution, and ap propriate photochemical quantum yields.