Atmospheric-pressure Penning ionization of aliphatic hydrocarbons.
A study has been made of the atmospheric-pressure Penning ionization (APPeI) of aliphatic hydrocarbons (pentane, hexane, heptane, and octane) with long-lived rare gas atoms (Rg*). The metastable rare gas atoms (He*, Ne*, Ar* and Kr*) were generated by the negative-mode corona discharge of atmospheric-pressure rare gases. In the Rg*APPeI mass spectra for aliphatic hyrocarbons, the relative abundances of fragment ions were found to increase in the order of He* --> Ne* --> Ar* --> Kr*. The order is in the opposite direction to the internal energies of the Rg*. The less fragmentation observed for He* may be because the nascent molecular ions [M(+.)]* formed by Penning ionization have lifetimes long enough for them to be collisionally deactivated in the atmospheric-pressure ion source. It was found that the relative abundances of fragment ions in Ar*APPeI increased when the sample pressure in the ion source was reduced. This is attributed to the collision of Ar* with molecular ions followed by fragmentation.
Hiraoka
Kenzo
K
Clean Energy Research Center, University of Yamanashi, Kofu 400-8511, Japan. hiraoka@yamanashi.ac.jp
Furuya
Hiroko
H
Kambara
Shizuka
S
Suzuki
Shigeo
S
Hashimoto
Yutaka
Y
Takamizawa
Atsushi
A