The chemistry of ionized acetone/Ar mixtures under varying gas flow and mole ratio conditions: a matrix-isolation study.

The chemistry of ionized acetone:Ar mixtures under varying total gas flow rate and acetone:Ar mole ratio conditions has been studied using matrix-isolation techniques. Gaseous acetone diluted in excess argon gas was subjected to electron bombardment with 300-eV electrons. The products of subsequent reaction processes were matrix isolated and analyzed by Fourier transform infrared (FTIR) absorption spectroscopy. Products included 1-propen-2-ol (the enol isomer of acetone), methane, ketene, carbon monoxide, ethane, ethene, acetylene and tricarbon monoxide. Variations in the total flow rate of gas resulted in changes in the efficiency of product formation without significant changes in the relative amounts of the major species formed. Variations in the acetone:Ar mole ratio at fixed total gas flow resulted in striking variations in the products formed, demonstrating a shift from single acetone molecule-derived charge-transfer ionization chemistry at low acetone mole ratios, to processes consistent with the participation of two or more acetone molecules at intermediate mole ratios. These results are interpreted in the context of ion-molecule reaction processes, the onset of which occurs at intermediate acetone mole ratios. Ethane dehydrogenation products are proposed to result from product secondary ionization, a process that is prevalent at high ionizing electron fluxes.