Dynamical traps lead to the slowing down of intramolecular vibrational energy flow

Abstract

The phenomenon of intramolecular vibrational energy redistribution (IVR) is at the heart of chemical reaction dynamics. Statistical rate theories, assuming instantaneous IVR, predict exponential decay of the population with the properties of the transition state essentially determining the mechanism. However, there is growing evidence that IVR competes with the reaction timescales, resulting in deviations from the exponential rate law. Dynamics cannot be ignored in such cases for understanding the reaction mechanisms. Significant insights in this context have come from the state space model of IVR, which predicts power law behavior for the rates with the power law exponent, an effective state space dimensionality, being a measure of the nature and extent of the IVR dynamics. However, whether the effective IVR dimensionality can vary with time and whether the mechanism for the variation is of purely quantum or classical origins are issues that remain unresolved. Such multiple power law scalings can lead to surprising mode specificity in the system, even above the threshold for facile IVR. In this work, choosing the well-studied thiophosgene molecule as an example, we establish the anisotropic and anomalous nature of the quantum IVR dynamics and show that multiple power law scalings do manifest in the system. More importantly, we show that the mechanism of the observed multiple power law scaling has classical origins due to a combination of trapping near resonance junctions in the network of classical nonlinear resonances at short to intermediate times and the influence of weak higher-order resonances at relatively longer times.phase space | wavelets | Arnold web | Fermi resonance | mode specificity U nderstanding, quantifying, and manipulating chemical reactions have been holy grails of chemical physics for nearly a century. In this continuing quest a fundamental and formidable phenomenon that needs to be reckoned with is that of intramolecular vibrational energy redistribution (IVR) (1-5). Although models of reaction rates like the Rice-Ramsperger-Kassel-Marcus (RRKM) theory and transition state theory (TST) continue to be of immense value in terms of their conceptual elegance and ease of application, the deviations from these paradigms due to incomplete IVR can lead to a deeper understanding of reaction dynamics and control (6, 7). Recent studies in both gas (8, 9) and condensed phases (10, 11) indicate that a detailed knowledge of the mechanism of IVR is a prerequisite for formulating dynamically consistent rate theories and, possibly, novel control strategies. Despite the challenges that arise due to the sheer complexity and richness of the IVR process (1), significant advances have been made over the past couple of decades, using a combination of innovative experimental techniques (12, 13) and novel theoretical approaches (14, 15).The present work focuses on one such novel theoretical approach, based on an analogy between IVR and the phenomenon of Anderson localization, proposed in the seminal work of Logan ...

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“…section II A for details). There are reasons to believe that these junctions are the seeds for classically nonstatistical dynamics [42,70,74]. It is therefore of some interest to investigate as to whether the signatures of such resonance junctions manifest in the corresponding quantum dynamics.…”

What is the mechanism of power-law distributed Poincaré recurrences in higher-dimensional systems?

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