title: Anomalous decline of molecular ion mobility in cooled helium gas.
abstract: We present a first successful theoretical account of the ion mobilities of and in helium gas at 4.3 K. Measured mobilities of various molecular ions at low effective temperatures reportedly tend to values smaller than their polarization limits, with the exception of N(2)(+). The present theoretical results obtained by the classical trajectory calculations agree with the experimental ones very well, and make it definitive that the anomalous decline of molecular ion mobility is caused by a Feshbach-like resonance due to the anisotropic interaction potential between a molecular ion and a helium atom. The mechanism thus revealed is supported by quantitative quantum mechanical calculations. The process appears very similar to that of laser cooling.
authors.affiliation: Department of Applied Physics and Chemistry, The University of Electro-Communications, Chofu, Tokyo 182-8585, Japan. ohtsuki@e-one.uec.ac.jp
authors.forename: Kazumasa
authors.initials: K
authors.lastname: Ohtsuki
authors.forename: Masatoshi
authors.initials: M
authors.lastname: Hananoe
authors.forename: Michio
authors.initials: M
authors.lastname: Matsuzawa