Condensation of supersaturated vapor. VII. The photoinduced nucleation of o-tolualdehyde and its underlying reaction mechanism

Abstract

On illuminating a supersaturated vapor containing a low concentration of o-tolualdehyde with ultraviolet light, nucleation occurs. This paper presents values for the diffusivity of the photonucleator and measurements of the quenching effects of NO on the rate of nucleation. These diffusivities lead to lower limits for the radius of the photonucleators of 4.5 to 8.7 Å, depending on which supersaturated vapor is used. A numerical simulation of the quenching effects of NO, assuming photoinduced nucleation occurs via a radical mechanism, was also made. The measured quenching effect agree qualitatively with those predicted by the simulation. We conclude that the photonucleators are photoproducts resulting from the reaction of photoexcited o-tolualdehyde with other vapor phase molecules. The reaction mechanism depends on the wavelength of the ultraviolet excitation light and the chemical reactivity of the supersaturated vapor, and may be a radical reaction mechanism. In the presence of NO, the reaction mechanism changes.