Increased recombination of CH3 radicals on stainless steel

By using a so-called ‘stream technique’, which consists of flowing gas in laminar regime along a quartz tube, we determine that CH3 radicals are completely removed from the pumped mixture (CH4/CXHY/H2/H/CH3) after several hundred collisions with the inner surface of a stainless steel insert (T = 380–470 K). The methyl sticking coefficient decreased to ∼10−6 and the recombination coefficient increased up to ∼0.01 at impingement with the metal surface. After passing through the heated zone no hydrocarbon deposition occurred at 300 K. However, unsaturated hydrocarbons, which formed in discharge zone and appeared as a result of interaction of radicals with stainless steel, condensed in a liquid phase at a temperature of ∼130 K and partial pressure of 0.01–0.1 Pa. Liquid films underwent partial polymerization and formed island deposits, which were stable at 300 K.