The Mobilities of NO+(CH3CN)n Cluster Ions (n=0-3) Drifting in helium-Acetonitrile Mixtures

Published

December 1, 1996

Author(s)

J A. de Gouw, L N. Ding, M Krishnamurthy, H S. Lee, E B. Anthony, V M. Bierbaum, S R. Leone

Abstract

The mobilities of NO+(CH₃CN)_n cluster ions (N=0-3) drifting in helium and in mixtures of helium and acetonitrile (CH₃CN) are measured in a flow-drift tube. The mobilities in helium decrease with cluster size (the mobility at zero field, K_o^(o), is 22.4+or-}0.5 cm² V^-1s^-1 for NO⁺, 12.3+or-}0.3 cm² V^-1s^-1 for NO+(CH₃CN)₂ and 7.9+or-}02 cm² V^-1s^-1 for NO⁺(CH₃C)_{3) but depend only weakly on the characteristic parameter E/N (electric field strength divided by the number density of the buffer gas). The size dependence is explained in terms of the geometric cross sections of the different cluster ions. The rate constants for the various cluster formation and dissociation reactions have also been determined in order to rule out the possibility that reactions occurring in the drift region influence the measurements. Since high pressures of acetonitfile are required to form NO}u+^(CH₃CN)₂ and NO⁺(CH₃CN)₃, the drift velocities for these ions are found to be strongly dependent on the acetonitrile concentration, as a result of the anomalously small mobilities of these ions in scetonitrile (K_o^(o)=0.041+or-}0.004 cm²V^-1s^-1 for NO⁺(CH₃CN)₂ and 0.044+or-}0.004 cm₂V^-1s^-1 for NO⁺(CH₃CN)₃). These values are at least an order of magnitude smaller than any previously reported ion mobility, and can be partly explained by the large ion-permenent dipole interaction between the cluster ions and acetonitrile. The remaining discrepancies may be the result of ligand exchang or the transfer of kinetic energy into internal energy of the cluster ion and the buffer gas molecule.

Citation

Journal of Chemical Physics

Volume

105

Issue

No. 23

Pub Type

Journals

Keywords

cluster ions, ion mobility

Citation

de Gouw, J. , Ding, L. , Krishnamurthy, M. , Lee, H. , Anthony, E. , Bierbaum, V. and Leone, S. (1996), The Mobilities of NO⁺(CH₃CN)n Cluster Ions (n=0-3) Drifting in helium-Acetonitrile Mixtures, Journal of Chemical Physics (Accessed May 1, 2024)