Comparison of the experimental mobility equivalent diameter for small cluster ions with theoretical particle diameter corrected by effect of vapour polarity

We investigate the effect of the vapour polarity on the mobility and size of ion clusters. The interaction of the neutral polar molecules with the electrical field of the charged particle/cluster may lead to significant change in the theoretical particle diameter and the corresponding mean ion mobility. The observed deviation between the theoretical Kelvin–Thomson diameter and the Millikan–Fuchs mobility equivalent diameter derived from the experimental data is explained. We suggest that in the size range of ∼1–2 nm the classical Millikan–Fuchs relationship remains valid and propose a modified version of the Kelvin–Thomson equation accounting for the dipole-charge interaction.