Quantum dynamics of energy transfer between bonds in coupled Morse oscillator systems

Abstract

The quantum dynamic flow of energy between coupled anharmonic bonds is calculated and analyzed for ABA triatomics with a massive central atom. The time dependence of quantum ‘‘normal mode’’ states is found to be classical in nature, but for states which are classically local, purely quantum energy flow between bonds occurs. We show that the mechanism for this quantum energy flow between local modes can be understood as an indirect state-to-state flow of probability, involving normal mode intermediary states. In particular, there is a regime in which rapid energy flow—which is classically forbidden—occurs from nonclassical states in the quantum case. Criteria are presented for the existence of purely quantum, and classically impossible, flow of energy between oscillators. Initially prepared states are accordingly classified as normal mode states, quantum local mode states, or nonclassical states, according to the extent and rate of bond–bond energy flow, the sensitivity of the process to small asymmetries, and the participation of intermediary states in the probability flow. Implications for intramolecular energy flow in large molecules and the connection with ‘‘dynamic tunneling’’ are discussed.