Modulations in the abundance of salt clusters in electrosprays

The abundance of tetraheptylammonium bromide clusters produced from formamide solutions by electrospray ionization (ESI) is investigated. It exhibits a wavy pattern when plotted as a function of cluster size, successive waves being ordered according to the initial cluster charge z. This structure confirms the ion evaporation mechanism of Iribarne and Thomson and simplifies drastically the determination of the distribution of cluster charge z and radius R, from which the kinetics of ion evaporation from charged drops can be inferred.