Gas Phase Reactions between Acetylene Radical Cation and Water. Energies, Structures and Formation Mechanism of C2H3O+ and C2H4O+• Ions

Reactions of the acetylene radical cation (C2H2 +•) with H2O were investigated using ion mobility mass spectrometry. The primary products are the C2H3O+ and C2H4O+• ions, produced with an overall rate coefficient k(300 K) = 2(±0.6) × 10−11 cm3 s−1 that increases with decreasing temperature. The C2H4O+• (adduct) vs C2H3O+ (H loss) ratio also increases with decreasing temperature, and with increasing third-body pressure. Ab initio calculations on the products showed seven stable C2H3O+ isomers and eleven stable C2H4O+• isomers. In the C2H4O+• adduct channel, the reactivity and energetics suggest that the adduct is the H2CCHOH+• (vinyl alcohol) ion. In the C2H3O+ channel, the H loss occurs exclusively from water. The C2H3O+ product ion undergoes slow deprotonation by water to form H+(H2O) n clusters. The reactivity, combined with energetics, suggests that the protonated ketene CH2COH+ is the most likely observed C2H3O+ ion probably with some contribution from the cyclic c-CH2CHO+ ion.