Laser-Induced Ionization and Mobility Measurements of Very Small Particles in Premixed Flames at the Sooting Limit

Laser-induced ionization signals are observed in a premixed C2H2/air flame at the sooting limit and are attributed to thermal ionization of very small particles. The mobilities of these species are derived from ion velocity measurements and compared with the mobility of Na+ for identical flame conditions. From a series of measured mobilities, estimates are made for the particle mass (2300-6100 amu) and diameter (1.6-2.2 nm). This experimental method is thus a new optical means for probing the early stages of soot formation.