A reinvestigation of the gas phase reaction of boron atoms, 11B(2Pj)/10B(2Pj) with acetylene, C2H2(X1Σg+)

The reaction dynamics of ground state boron atoms, B(2Pj), with acetylene, was reinvestigated and combined with novel electronic structure calculations. Our study suggests that the boron atom adds to the carbon-carbon triple bond of the acetylene molecule to yield initially a cyclic intermediate undergoing two successive hydrogen atom migrations to form ultimately an intermediate i3. The latter was found to decompose predominantly to the c-BC2H(X2A′) isomer plus atomic hydrogen via a tight exit transition state. To a minor amount, an isomerization of i3-i4 prior to a hydrogen atom ejection forming the linear structure, HBCC(X1Σ+), has to be taken into account. Since the c-BC2H(X2A′) and HBCC(X1Σ+) isomers are separated by an isomerization barrier to ring closure of only 3 kJ mol−1, internally excited HBCC(X1Σ+) products can isomerize to the c-BC2H(X2A′) structure and vice versa.