Mechanism of Formation of o-Methylbenzyl Radical by Photodissociation of o-Xylene in Solution

Article abstract of DOI:10.1021/j100073a020

Photodissociation of o-xylene in room temperature n-heptane solution has been studied by means of two-pulse laser-induced fluorescence and transient absorption spectroscopy.Excitation of o-xylene at 266 nm into the S₁ state causes the molecule to undergo carbon-hydrogen bond homolysis in its methyl group, resulting in formation of the o-methylbenzyl radical.The fluorescence of the o-methylbenzyl radical has been observed around 500 nm with a lifetime of 4.1 +/- 1.0 ns, when it has been excited with a 308-nm pulse after the photolysis pulse.The absorption of the o-methylbenzyl radical has been obtained with maxima at 309 and 320 nm.The formation raet constant of the o-methylbenzyl radical, (3.1 +/- 0.4)E7 s^-1, agrees with the decay rate constant of the fluorescence of o-xylene, (2.7 +/- 0.3)E7 s^-1.It is concluded that excitation with one photon at 266 nm followed by vibrational relaxation populates the thermal equilibrium.S₁ state of o-xylene, from which predissociation occurs.