On the formation of ethynylbiphenyl (C14D5H5; C6D5C6H4CCH) isomers in the reaction of D5-phenyl radicals (C6D5; X2A1) with phenylacetylene (C6H5C2H; 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 (C6D5C8H6) 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.