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



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


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.
Journal of Chemical Physics
No. 2


cluster ion mobilities, ion-dipole interactions, kinetics


Krishnamurthy, M. , de Gouw, J. , Ding, L. , Bierbaum, V. and Leone, S. (1997), Mobilities and Formation Kinetics of NH<sub>4</sub><sup>+</sup>(NH<sub>3</sub>)<sub>n</sub> Cluster Ions (n=0-3) in helium and helium/ammonia mixtures, Journal of Chemical Physics (Accessed July 18, 2024)


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Created December 31, 1996, Updated October 12, 2021