title: Alternating-gradient focusing of the benzonitrile-argon van der Waals complex.
abstract: We report on the focusing and guiding of the van der Waals complex formed between benzonitrile molecules (C(6)H(5)CN) and argon atoms in a cold molecular beam using an ac electric quadrupole guide. The distribution of quantum states in the guided beam is non-thermal, because the transmission efficiency depends on the state-dependent effective dipole moment in the applied electric fields. At a specific ac frequency, however, the excitation spectrum can be described by a thermal distribution at a rotational temperature of 0.8 K. From the observed transmission characteristics and a combination of trajectory and Stark-energy calculations we conclude that the permanent electric dipole moment of benzonitrile remains unchanged upon the attachment of the argon atom to within ±5%. By exploiting the different dipole-moment-to-mass ([micro sign]/m) ratios of the complex and the benzonitrile monomer, transmission can be selectively suppressed for or, in the limit of 0 K rotational temperature, restricted to the complex.
authors.affiliation: Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin, Germany.
authors.forename: Stephan
authors.initials: S
authors.lastname: Putzke
authors.forename: Frank
authors.initials: F
authors.lastname: Filsinger
authors.forename: Jochen
authors.initials: J
authors.lastname: Küpper
authors.forename: Gerard
authors.initials: G
authors.lastname: Meijer
mesh_terms: D001128:Argon / Q000737:chemistry*; D057927:Hydrophobic and Hydrophilic Interactions; D009570:Nitriles / Q000737:chemistry*
chemical_list: D009570:Nitriles; D001128:Argon; C014356:benzonitrile