Mobilities and Formation Kinetics of NH4+(NH3)n Cluster Ions (n=0-3) in helium and helium/ammonia mixtures

Published

January 1, 1997

Author(s)

M Krishnamurthy, J A. de Gouw, L N. Ding, V M. Bierbaum, S R. Leone

Abstract

NH₄⁺(NH₃)_n (n=1-3) cluster ions are formed in a field free flow tube section of a selected ion flow-drift tube (SIFDT) apparatus. The rate constants or the cluster ion formation and dissociation reactions are measured. Cluster ion mobilities measured in mixtures of HE and NH₃ are used to obtain the individual mobilities in helium and ammonia by applying Blanc's law to the mixtures. NH₄⁺ ion mobilities in helium, obtained by using Blanc's law, compare very well with those measured in pure helium and also with previous measurements. The zero-field mobilities of the cluster ions in helium (22.1 +or-}0.3 cm²V^-1s^-1 for NH₄⁺, 16.6 +or-} 0.2 cm²V^-1s^-1 for NH₄⁺(NH₃), 12.2 +or-} 0.3 cm²V^-1s^-1 for NH₄⁺(NH₃)₂ and 12.1 +or-}0.4 cm²V^-1s^-1 for NH₄⁺(NH₃)₂) decrease with increasing size of the cluster, which can be explained in terms of the geometric cross sections of the different cluster ions. The zero-field mobilities of NH₄⁺(0.94 +or-} 0.15 cm²V^-1s^-1) and NH₄⁺9NH₃)(0.83 +or-} 0.16 cm²V^-1s^-1) in ammonia compare very well with those computed by calculating the collision cross section, with the ion-dipole interactions taken into account. The zero-field mobilities of the larger clusters (0.45 +or-} 0.20 cm²V^-1s^-1 for NH₄⁺(NH₃)₂ are significantly lower than the computed values, possibly due to more prominent solvent exchange reactions and efficient transfer of kinetic energy into internal energy of the cluster ion and the buffer gas molecules.

Citation

Journal of Chemical Physics

Volume

106

Issue

No. 2

Pub Type

Journals

Keywords

cluster ion mobilities, ion-dipole interactions, kinetics

Citation

Krishnamurthy, M. , de Gouw, J. , Ding, L. , Bierbaum, V. and Leone, S. (1997), Mobilities and Formation Kinetics of NH₄⁺(NH₃)_n Cluster Ions (n=0-3) in helium and helium/ammonia mixtures, Journal of Chemical Physics (Accessed December 12, 2024)