Influence of vibrational frequency mismatch on phase-space bottlenecks to intramolecular energy redistribution and molecular fragmentation

Abstract

We report studies of classical models of unimolecular fragmentation of van der Waals complexes using the methodologies of Hamiltonian mappings and flows. The effect of frequency mismatch between harmonic molecular vibrations of a host molecule and the van der Waals bond-stretching motion is shown to dominate vibrational energy redistribution and fragmentation. Our results show that a crossover exists when the frequency mismatch is increased from a stochastic regime of resonances between the nonlinear oscillators to a regular regime where the system behaves like an integrable system. Our model systems include both collinear and T-shaped oscillator displacement configurations, as well as a many-oscillator system that included both classes of motions. Oscillator parameter ranges were used that approximate vibrations in C6H6⋅He and C6H6⋅Ar van der Waals complexes.

New developments in classical chaotic scattering

“…Even if the motion is simple in the field free case, external driving generically destroys integrability and leads to fragmentation or ionization. The study of such systems has also attracted recent interest and serves as a useful model for the dissociation of molecules (see [76]) or ionization of atoms [77]. The contribution shown in [78] is devoted to a periodically driven scattering system and points out that parabolic orbits also generate a power law decay.…”

Microcanonical rates, gap times, and phase space dividing surfaces

“…The multimode case remains less thoroughly explored and understood. Methods for defining approximate intramolecular bottlenecks and reactive dividing surfaces have been devised 78,79,80,81,82,83,84 . Although the Arnold web of resonances provides a useful framework for mapping and analyzing evolution of phase points in near-integrable multimode systems 51,85 , so-called "Arnold diffusion" 51,86 has become a convenient but often ill-defined catchall term employed to describe a variety of possibly distinct phase space transport mechanisms in N ≥ 3 DoF systems 87 .…”

“…Methods for defining approximate intramolecular bottlenecks and reactive dividing surfaces have been devised. [115][116][117][118][119][120][121] Although the Arnold web of resonances provides a useful framework for mapping and analyzing evolution of phase points in near-integrable multimode systems, 86,122 so-called Arnold diffusion 86,123 has become a convenient but often ill-defined catchall term employed to describe a variety of possibly distinct phase space transport mechanisms in N Ն 3 DoF systems. 124 The possible role of "Arnold diffusion" in multimode molecular systems has been studied in IVR ͑Refs.…”

Scaling Perspective on Intramolecular Vibrational Energy Flow: Analogies, Insights, and Challenges

“…Instead, the hydrogen atom remains tethered to the HCO moiety. The weak tether in this case is reminiscent of earlier studies on the vibrational predissociation dynamics [49] of van der Waals molecules wherein IVR dynamics plays a central role. Second point is that the roaming mechanism was theoretically confirmed by Bowman and coworkers using classical dynamics on the ab initio potential energy surface.…”