High Resolution Electronic Spectroscopy of o- and m-Toluidine in the Gas Phase. Barrier Height Determinations for the Methyl Group Torsional Motions

High resolution electronic spectra of o- and m-toluidine have each been recorded for the S(1)<--S(0) origin band transitions of the isolated molecules. Each spectrum is split into two sub-bands owing to tunneling motions along the methyl group torsional coordinate. Analyses of these data provide information about the preferred configurations of the methyl groups and the barriers opposing their motions in both the ground and excited electronic states. Despite their apparent similarities, the experiments reveal that these properties are quite different in the two molecules. Possible reasons for this behavior are discussed.