The atmospheric pressure Penning ionization was applied to the analysis of atmospheric-pressure ambient gaseous samples. The metastable rare gas atoms (Rg῏) were produced by a negative-mode corona discharge of reagent rare gas (Rg). The rare gas containing Rg῏ in the discharge cell flowed out into the ion source cell through a nozzle with an inner diameter of 1 mm as a jet stream. The jet stream acts as a gas-jet pump and the pressure of the ion source cell becomes somewhat lower than the atmospheric pressure. The sample gas at ambient atmospheric pressure was sucked into the reduced-pressure ion source cell through the stainless steel tube (10 cm in length, 1 mm in diameter). The sample gases introduced in the ion source cell are ionized by Penning ionization. This technique was found to be applicable to various gaseous samples such as aromatic compounds, oxygen-and nitrogen-containing compounds, etc. However, no ion signal could be detected for aliphatic hydrocarbons. This may be due to the much smaller ionization cross sections for these compounds than N2 and O2 molecules which are introduced into the ion source together with sample gases.
Gas-phase ion/molecule reactions in tetrafluoroethylene (C2F4) were studied with a pulsed electron beam mass spectrometer. When a few Torr of major gas, N2, containing 1῎10 mTorr C2F4 was ionized by 2 keV electrons, CF3ῌ and C2F4 ῌ were formed as major ions. CF3 ῌ reacted with C2F4 rapidly to form C3F7 ῌ . The rate constant of reaction C2F4 ῌ ῌC2F4ΐC3F5 ῌ ῌCF3 was measured to be (1.5῍0.5)῎10῍11 cm 3 /moleculeῌs and found to be temperature-independent in the range of 180῎310 K.
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