Ion mobility of precritical clusters in supersaturated vapors: Condensation of supersaturated methanol vapor induced by toluene and styrene ions

A new method for measuring the ion mobility of precritical clusters in supe rsaturated vapors is reported. The method is based on the REMPI (Resonance Enhanced Multiphoton Tonization) nucleation technique, which allows the gen eration of selected ions within a supersaturated host vapor held in a diffu sion cloud chamber. The precritical cluster ions drift under the influence of a uniform electric field to the nucleation zone, where they become conde nsation nuclei and rapidly grow into macroscopic liquid droplets that can b e detected by light scattering. The reduced mobility of the precritical clu sters in the toluene(+)/methanol and styrene(+)/methanol systems decreases with increasing methanol supersaturation, which reflects the increase in th e size of the solvated ion in agreement with Thomson's model for ion-induce d nucleation.