Dynamics of Methyl Radical Formation Following 266 nm Dissociative Photoionization of Dimethyl- and Trimethyl- Pyridines

The 266 nm photolysis of various positional isomers of dimethylpyridines (DMPs) and trimethylpyridine (TMP) was investigated by measuring the translational energy distribution of methyl radical following {sp2}C−C{sp3} bond dissociation. The observed translational energy distribution is attributed to the dissociative photoionization in the cationic ground state following [1+1+1] three-photon absorption. The translational energy distribution profiles of the methyl radical were broad with the maximum translation energy in the excess of 2 eV, which originates due to the dissociation of {sp2}C−C{sp3} bond ortho to nitrogen atom in the ring. The dynamics of {sp2}C−C{sp3} bond dissociation in the cationic ground state of methyl pyridines is marginally dependent on the number and position of the methyl groups, however is site selective with preferential cleavage of the C−C bond in the ortho position to the pyridinic nitrogen atom.