On the formation of ethynylbiphenyl (C₁₄D₅H ₅; C₆D₅C₆H₄CCH) isomers in the reaction of D5-phenyl radicals (C₆D₅; X ²A₁) with phenylacetylene (C₆H ₅C₂H; X¹A₁) under single collision conditions

Reaction dynamics of the D5-phenyl radical with phenylacetylene were investigated in crossed molecular beams at a collision energy of 120.7 kJ mol^-1 supported by ab initio calculations. The reaction displays indirect, complex forming scattering dynamics, and adduct formation, with D5-phenyl attacking the phenyl ring of phenylacetylene at the ortho, meta and para positions over small entrance barriers. The adduct (C₆D ₅C₈H₆) undergoes hydrogen emission through tight exit transition states of 34-47 kJ mol^-1 above the separated products. The phenyl addition-hydrogen elimination mechanism produces various ethynylbiphenyls exoergically by 25-38 kJ mol^-1. No phenanthrene was formed under our experimental conditions.