Argon mediated electron impact ionization of Arn(CH3OH)m heteroclusters

In this paper we have contrasted electron impact cluster mass spectra of a methanol/argon expansion with a methanol/helium expansion and have measured appearance potentials for several of the prominent ions in each case. We have observed a number of ionic species in the argon expansion (i.e., CHxO+ where x=0–4) which are not observed in the helium expansion. Appearance potentials for these species fall in the region 11.3–11.8 eV indicating that the threshold ionization of Arn(CH3OH)m heteroclusters is mediated by the Ar 4s excited states (3P2,0;11.55 and 11.72 eV). This represents the first time that intracluster Penning ionization has been positively identified using electron impact measurements.