Observation of CH2 radical and comparison with CH3 radical in a rf methane discharge

Methylene radical (CH2) in a rf methane discharge was detected using threshold ionization mass spectrometry. The absolute density of CH2 radical (∼109 cm−3) for the discharge in 10 mTorr CH4 with 10 W rf power was two orders of magnitude less than the density of methyl radical (CH3). The CH2 density in the afterglow of a pulsed rf discharge turned out to decay on a time scale (≤10 ms) much shorter than the decay time of CH3 radical (∼100 ms). The observed rapid loss of CH2 radical was attributed to a large sticking coefficient and the resultant surface loss, in addition to gas phase losses due to the CH2 reactions with CH3 and CH4.