Ab initio study of C4H3 potential energy surface and reaction of ground-state carbon atom with propargyl radical

The potential energy surface for the reaction of the ground-state carbon atom [C(Pj)] with the propargyl radical [HCCCH2(XB1)] is investigated using the G2M(RCC,MP2) method. Numerous local minima and transition states for various isomerization and dissociation pathways of doublet C4H3 are studied. The results show that C(Pj) attacks the π system of the propargyl radical at the acetylenic carbon atom and yields the n-C4H3(2A′) isomer i3 after an 1,2-H atom shift. This intermediate either splits a hydrogen atom and produces singlet diacetylene, [HCCCCH (p1) + H] or undergoes (to a minor amount) a 1,2-H migration to i-C4H3(2A′) i5, which in turn dissociates to p1 plus an H atom. Alternatively, atomic carbon adds to the triple C≡C bond of the propargyl radical to form a three-member ring C4H3 isomer i1, which ring opens to i3. Diacetylene is concluded to be a nearly exclusive product of the C(Pj) + HCCCH2 reaction. At the internal energy of 10.0 kcal/mol above the reactant level, Rice–Ramsperger–Kassel–Marcus calculations show about 91.7% of HCCCCH comes from fragmentation of i3 and 8.3% from i5. The other possible minor channels are identified as HCCCC + H2 and C2H + HCCH. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 1522–1535, 2001 Correspondence to: A. M. Mebel; e-mail: [email protected]. edu.tw ∗Present address: Department of Chemistry, University of York, York YO10 5DD, U.K. Contract/grant sponsors: Petroleum Research Fund of Taiwan; Academia Sinica Contract/grant sponsor: National Science Council of Taiwan, R.O.C.; contract/grant numbers: 8902113-M-001-034 and 8902113-M-001-069 This article includes Supplementary Material available from the authors upon request or via the Internet at ftp.wiley. com/public/journals/jcc/suppmat/22/13 or http://www.interscience.wiley.com/jpages/0192-8651/suppmat/v22.1522.html Journal of Computational Chemistry, Vol. 22, No. 13, 1522–1535 (2001) © 2001 John Wiley & Sons, Inc. PES FOR C(Pj) REACTION WITH HCCCH2(XB1)