The species resulting from a microwave discharge in polyhalogenated methanes were investigated using their reactivity with Ar+, Cl-, and FeCO+ probe ions. With discharge off, reaction of FeCO+ with most of these substrates led mainly to halomethyl cations along with a (XFeCO) neutral species in which the CO molecule probably remains bound to the metal. With discharge on, completely different products were observed : for fluorinated substrates Pyrex etching yielded silicon and boron fluorides, with COBr2 formation in the case of CF3Br. Molecular chlorine or bromine were formed from chlorine- or bromine-containing halomethanes, along with hydrogen halides in the case of hydrogen-containing substrates. Discharge mixtures from CFCl3 or CHCl3 contained CCl4. No recombination by carbon-carbon bond formation leading to dimers or oligomers was detected.