Mass spectroscopic investigation of the CH3 radicals in a methane rf discharge

Abstract

Neutral CH₃ radicals in a capacitively coupled rf discharge in methane have been detected with a quadrupole mass spectrometer utilizing a threshold ionization technique. The absolute density of CH₃ radicals was measured at pressures from 0.5 to 20 mTorr, together with the ionic composition of the methane plasma. The principal ionic species were CH⁺₅ and C₂H⁺₅ , except in the low‐pressure region, suggesting the importance of ion‐molecule reactions in the plasma. The lifetime of CH₃ radicals in the afterglow of pulsed rf discharges was measured and explained in terms of the recombination reaction CH₃ +CH₃ →C₂ H₆.