Cluster ion formation of alkali halides by electrospray droplet impact

Positive and negative cluster ions formed by electrospray droplet impact on the alkali halides (MX) were measured for all alkali halides. Small amounts of powder samples deposited and crushed into thin films on the metal substrate were served for the measurement. The size distribution of cluster ions is very limited for LiF, CsF, and LiI. Little or no fluoride cluster ions F−(MF)n were detected. In general, distribution of n for negative cluster ions X−(MX)n is narrower than that for positive cluster ions M+(MX)n, probably due to the instability caused by the mutual Coulomb repulsion between the larger-size halide ions than alkali ions. While the cubic-like structures are preferred for alkali halides with smaller ionic radii, the stacked hexagonal structures with n = 3, 6, and 9 are preferred for those with larger ionic radii.