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Abstract

A radical beam source for methyl radicals (CH3) was characterized applying ionization-threshold mass spectrometry .The beam source is based on thermal dissociation of methane (CH4) or azomethane (N2(CH3)2) in a heated tungsten capillary. A flux of (3 1) E13 cm{-2} sec{-1} CH3 radicals is produced using methane as precursor gas and a capillary temperature of 1650 K. Alternatively, a flux of (3 1) E14 cm{-2} sec{-1} CH3 is produced using azomethane as precursor gas and a capillary temperature of 1150 K. The dominant production of methyl from the precursor methane occurs due to reaction 2 CH4+M--2 CH3+H2+M at the hot tungsten surface. The dominant production of methyl from azomethane occurs due to the reaction N2(CH3)2-- 2 CH3+N2. Besides methyl radicals, only stable molecules contribute to the emitted flux; within the detection limit, no atomic hydrogen is observed. From the comparison of ionization-threshold mass spectrometry and standard mass spectrometry, it is concluded that the cracking pattern of methane varies with the methane gas temperature. This is explained by the vibrational assisted dissociation of methane.

Additional information

Authors: SCHWARZ-SELLINGER T, Max-Planc Institut fur Plasmaphysik, Euratom Association, Boltzmannstrausse 2, D-85748 Garching bei Munchen (DE);DOSE V, Max-Planc Institut fur Plasmaphysik, Euratom Association, Boltzmannstrausse 2, D-85748 Garching bei Munchen (DE);JACOB W, Max-Planc Institut fur Plasmaphysik, Euratom Association, Boltzmannstrausse 2, D-85748 Garching bei Munchen (DE);VON KEUDELL A, Max-Planc Institut fur Plasmaphysik, Euratom Association, Boltzmannstrausse 2, D-85748 Garching bei Munchen (DE)
Bibliographic Reference: Article: J. Vac. Sci. Technol. A 19(1) (2001), pp. 101-107
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