Tn. Le et al., Ab initio MO study of the triplet C3H4 potential energy surface and the reaction of C(P-3(j)) with ethylene, C2H4, J PHYS CH A, 105(10), 2001, pp. 1847-1856
The potential energy surface for the reaction of C(P-3(j)) with ethylene, C
2H4((XAg)-Ag-1), has been investigated using the G2M method. Structures of
the stationary points and transition states for various isomerization and d
issociation pathways of triplet C3H4 have been studied. The results show th
at at the initial step of the C(P-3(j)) + C2H4(X(1)A(g)) reaction carbon at
om attacks the pi -orbital of the C2H4 molecule yielding cyclopropylidene i
i without entrance barrier, ii then isomerizes to the triplet allene i3 via
ring opening. The latter either splits a hydrogen atom producing the propa
rgyl radical p3 + H or undergoes a 1,2-H shift to vinylmethylene, which in
turn gives H2CCCH (p3) + H. The propargyl radical is concluded to be a near
ly exclusive product of the C(P-3) + C2H4 reaction. At the internal energy
of 9.2 kcal/mol above the reactants level, Rice-Ramsperger-Kassel-Marcus ca
lculations show about 93% of H2CCCH comes from fragmentation of triplet all
ene and 7% from vinylmethylene. The formation of CH2(B-3(1)) + C2H2 via the
vinylmethylene intermediate gives only 2% of the reaction products; the fo
rmation of triplet C3H2 + Hz is unlikely. This study completes a comprehens
ive investigation of the C(P-3(j)) + C2H4 reaction; its rate constants have
been measured in a broad temperature range from 10 to 800 K, the reaction
dynamics has been unraveled by crossed molecular beam experiments, and the
reaction potential energy surface has now been explored by ab initio calcul
ations.