Theoretical study on the mechanism of the reaction: HCCCH2(+)+C2H2 -> c-C3H3(+)+C2H2

The gas phase ion-molecule reaction of propargylium (HCCCH2+) with acetylen e (C2H2) to produce cyclopropenylium (c-C3H3+) with C2H2 has been investiga ted theoretically at the B3LYP/6-31G(d) and single-point QCISD/6-311G(d,p) levels. The detailed mechanism for the observed isotope exchange between HC CCH2+ and C2D2 has also discussed. Three intermediates 1 CH2CCH2CCH+, 2 H2C 2. CHCCH2+ and 3 c-C4H3-CH2+ are shown to play important roles in the produ ct formation and isotope exchange processes, rather than the low-lying isom ers 4 c-C3H2-CH2+, 7 c-(CH)(5)(+) and 8 pyramidal C5H5+. Our calculated res ults agree well with the available experimental data and may be helpful for understanding the mechanism for combustion processes. (C) 2001 Elsevier Sc ience B.V. All rights reserved.