Classical and quantum dynamical manifestations of index-2 saddles: concerted versus sequential reaction mechanisms

• URL: http://arxiv.org/abs/2009.07716v1
• Date: Wed, 16 Sep 2020 14:39:20 GMT
• Title: Classical and quantum dynamical manifestations of index-2 saddles: concerted versus sequential reaction mechanisms
• Authors: Priyanka Pandey, Shibabrat Naik and Srihari Keshavamurthy
• Abstract summary: We study the presence of higher index saddles on a multidimensional potential energy surface. We show that the ultrafast shift of the mechanism from a concerted to a stepwise one is essentially a classical dynamical effect.
• Score: 0.0
• License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/
• Abstract: The presence of higher index saddles on a multidimensional potential energy surface is usually assumed to be of little significance in chemical reaction dynamics. Such a viewpoint requires careful reconsideration, thanks to elegant experiments and novel theoretical approaches that have come about in recent years. In this work, we perform a detailed classical and quantum dynamical study of a model two degree of freedom Hamiltonian, which captures the essence of the debate regarding the dominance of a concerted or a stepwise reaction mechanism. We show that the ultrafast shift of the mechanism from a concerted to a stepwise one is essentially a classical dynamical effect. In addition, due to the classical phase space being a mixture of regular and chaotic dynamics, it is possible to have a rich variety of dynamical behaviour, including a Murrell-Laidler type of mechanism, even at energies sufficiently above that of the index-2 saddle. We rationalize the dynamical results using an explicit construction of the classical invariant manifolds in the phase space.

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