Formation of 1,3-hexadiene-5-yne by two-photon chemistry of benzene via hot molecule

The two-photon chemistry of gaseous benzene was studied by laser flash photolysis using an ArF laser (193 nm) pumping to the S2 state. The major product was assigned to 1,3-hexadiene-5-yne, and one of the minor products was the phenyl radical. The formation mechanism is suggested to be as follows: hot benzene (S0**) is formed by internal conversion from the S2 state, and hot benzene with two-photon energy (S0***) is formed from an excited state of S0**. S0*** is produced by a two-photon process, and its internal energy reaches 1243 kJ/mol. 1,3-Hexadiene-5-yne can form at rates much faster than the collision frequency (∼1010 s−1) under benzene 0.53 kPa in the presence of 51 kPa of propane. Collisional cooling is expected to quench the slow processes from S0** as well as the decomposition of 1,3-hexadiene-5-yne. 1,3-Hexadiene-5-yne and the phenyl radical can be the primary products of the two-photon fragments, which have been found by a multimass ion imaging technique.