Excitation of NH Stretching Modes in Aromatic Molecules: o-Toluidine and α-Methylbenzylamine

초록

Selectively excited o-toluidine and & alpha;-methylbenzylaminehave been studied with quasi-classical trajectory procedures to determinethe extent and timescales of intramolecular energy flow. The initialexcitation is in the stretching mode of the para-CHbond, and its flow is initiated by interaction with an argon atom.Energy flow to the NH stretching mode is the dominant relaxation pathway,and its effectiveness is enhanced strongly by the methyl-NHinteraction. Energy flow characteristics in both molecules are similar,but the flow is more effective in o-toluidine thanin & alpha;-methylbenzylamine because the methyl group bonded to thebenzene ring exerts stronger perturbation on the energy-flow pathwaythan the group bonded to the side chain. The relaxation of the initiallyexcited CH completes on a timescale of several picoseconds, but themain part of energy flow to the NH occurs on a subpicosecond scale.In o-toluidine, carbon-carbon overtone modeslead to ring-CC bonds gaining and transporting more energythan high-frequency CH bonds, but they all gain far less energy thanthe NH stretching mode.

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