Heterogeneous reactions of hydrogen atoms and methyl radicals with a diamond surface in the 300-1133 K temperature range

The heterogeneous reactions of H atoms and CH[sub 3] radicals with a polycrystalline diamond surface have been studied using discharge flow and pulsed excimer-laser photolysis techniques coupled with photoionization mass spectrometry. A random walk Monte Carlo solution of the three-dimensional diffusion equation was used to interpret the experimental data and to obtain the collisional efficiency for removal of hydrogen atoms by the diamond surface ([gamma][sub w]) over the temperature range 300-1119 K. The result expressed in Arrhenius form is [gamma][sub w](H on diamond) = 10[sup [minus]3.4[plus minus]0.3] + 10[sup 0.29[plus minus]0.15] exp(-(6020 [plus minus] 470)cal/RT). The second term is assigned to reaction 1, surface H atom abstraction by gas-phase H atoms, followed by the fast recombination reaction 2 of gas-phase H atom with the surface sites created by reaction 1. The experimentally measured [gamma][sub w] yielded the rate constant of reaction 1 (assuming the surface concentration of H atom, [H[sub s]] = 1.8 [times] 10[sup 15] molecule cm[sup [minus]2], and k[sub 2] [much gt] k[sub 1]): k[sub 1] = 10[sup [minus]10.06[plus minus]0.15] exp(-(6680 [plus minus] 470)cal/RT) cm[sup 3] molecule[sup [minus]1] s[sup [minus]1]. This expression for the rate constant is in good agreement with that for the gas-phase abstraction of tertiarymore » hydrogen atoms. The CH[sub 3](g) radical decay above the diamond film was studied over the temperature range 739-1133 K. 64 refs., 5 figs., 1 tab.« less