Ionisation and appearance potentials of CH4by electron impact

Authors:
  • PPP Plessis
    P Plessis
  • PMP Marmet
    P Marmet
  • RDR Dutil
    R Dutil
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Abstract
The CH4+electroionisation efficiency curve and the CH3+, CH2+, CH+and C+appearance potential curves are presented. The data were obtained by an apparatus of very high sensitivity with an improved electron monochromator. The CH4+ionisation potential is measured to be 12.63+or-0.02 eV. The results show that some previously reported appearance potential values should be corrected, in some cases by several electron volts. This is attributed to superior apparatus sensitivity. Ion-pair formation is clearly observed for the CH3+and CH+fragments. The CH+and C+appearance potentials have been detected down to adiabatic threshold. The stable fragment CH22+, is also observed.

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