Ion/molecule reaction pathways and reaction rate coefficients for both cyclic (cyclo-propenylium) and linear (propargylium) C3H3isomers reacting with aromatic hydrocarbons (benzene, toluene, indene, naphthalene, 1 - and 2-methyl naphthalenes) and alcohols (methanol, ethanol, n-butanol) at low pressures and near room temperature have been determined using ion cyclotron resonance (icr) mass spectrometric techniques. Rate coefficients near the Langevin limit were found for reactions of the propargylium isomer with most of the aromatic hydrocarbons, with charge and hydride transfer reactions predominating. Somewhat lou,er rate coefficients were determined for reactions of the propargylium isomer with the three alcohols, with proton, hydride, and OH-transfer representing the major reaction channels. Implications of these results for an ionic soot formation mechanism are discussed.