Conical shape fluctuations determine the rate of ion-evaporation and the emitted cluster-size distribution from multiple-charged droplets

The ion-evaporation mechanism (IEM) is perceived to be a major pathway for disintegration of multiple-ion charged droplets found in atmospheric and sprayed aerosols. However, the precise mechanism of IEM and the range of its validity have not been established yet despite its broad use in mass spectrometry and atmospheric chemistry over past half century. Here we present direct computational evidence of the mechanism by performing a systematic study over several kosmotropic and chaotropic ions. We find that in the parent droplet multiple kosmotropic ions are buried deeper below the droplet surface than chaotropic ions. This differentiation in the ion location is only captured by a polarizable model. We demonstrate that the emitted cluster-size distribution is determined by dynamic conical deformations and not from the equilibrium ion-depth within the parent droplet as the IEM models assume. We present critical factors that determine the cluster-size distribution such as the charge sign asymmetry that have not been considered in models and in experiments. We argue that the existing IEM analytical models do not establish a clear difference between IEM and Rayleigh fission.We propose a shift in the existing view for IEM from the equilibrium properties of the parent droplet to the chemistry in the conical shape fluctuations that lead to a single solvated-ion emission. Consequently, chemistry in the conical fluctuations may also be a key element to explain charge states of macromolecules in mass spectrometry and may have potential applications in catalysis.