title: Atmospheric-pressure Penning ionization of aliphatic hydrocarbons.
abstract: 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.
authors.affiliation: Clean Energy Research Center, University of Yamanashi, Kofu 400-8511, Japan. hiraoka@yamanashi.ac.jp
authors.forename: Kenzo
authors.initials: K
authors.lastname: Hiraoka
authors.forename: Hiroko
authors.initials: H
authors.lastname: Furuya
authors.forename: Shizuka
authors.initials: S
authors.lastname: Kambara
authors.forename: Shigeo
authors.initials: S
authors.lastname: Suzuki
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Hashimoto
authors.forename: Atsushi
authors.initials: A
authors.lastname: Takamizawa