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Physical Review C

Quantum-classical correspondence in microscopic and mesoscopic complex collisions

S. Yu. Kun, Alexei Vagov, Walter Greiner

Published Dec 20, 2000• 9 citations
Publisher

Abstract

We propose a novel method to study quantum-classical correspondence in complex, e.g., heavy-ion, atomic, molecular, and atomic cluster collisions. The many-body rotating wave packets are formed spontaneously and their stability is due to the slow decoherence between highly excited strongly overlapping states of the intermediate complex. The phenomenon is illustrated by analyzing the ${}^{12}{\mathrm{C}+}^{24}\mathrm{Mg}$ collision. The significant deviations from the random-matrix theory are reproduced in terms of the macroscopically rotating molecule formed in this collision.

DOI
10.1103/physrevc.63.014608

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•Aug 30, 2018•0 citations
We propose a novel method to study quantum-classical correspondence in complex, e.g., heavy-ion, atomic, molecular, and atomic cluster collisions. The many-body rotating wave packets are formed spontaneously and their stability is due to the slow decoherence between highly excited strongly overlapping states of the intermediate complex. The phenomenon is illustrated by analyzing the 12C+24Mg{}^{12}{\mathrm{C}+}^{24}\mathrm{Mg}12C+24Mg collision. The significant deviations from the random-matrix theory are reproduced in terms of the macroscopically rotating molecule formed in this collision.
We demonstrate a breakdown in the macroscopic (classical-like) dynamics of wave-packets in complex microscopic and mesoscopic collisions. This breakdown manifests itself in coherent superpositions of the rotating clockwise and anticlockwise wave-packets in the regime of strongly overlapping many-body resonances of the highly-excited intermediate complex. These superpositions involve $\ensuremath{\sim}{10}^{4}$ many-body configurations so that their internal interactive complexity dramatically exceeds all of those previously discussed and experimentally realized. The interference fringes persist over a time-interval much longer than the energy relaxation-redistribution time due to the anomalously slow phase randomization (dephasing). Experimental verification of the effect is proposed.
We study the effect of phase relaxation on coherent superpositions of rotating clockwise and anticlockwise wave packets in the regime of strongly overlapping resonances of the intermediate complex. Such highly excited deformed complexes may be created in binary collisions of heavy ions, molecules, and atomic clusters. It is shown that phase relaxation leads to a reduction of the interference fringes, thus mimicking the effect of decoherence. This reduction is crucial for the determination of the phase-relaxation width from the data on the excitation function oscillations in heavy-ion collisions and bimolecular chemical reactions. The difference between the effects of phase relaxation and decoherence is discussed.
We study coherent superpositions of clockwise and anticlockwise rotating intermediate complexes with overlapping resonances formed in bimolecular chemical reactions. Disintegration of such complexes represents an analog of a famous double-slit experiment. The time for disappearance of the interference fringes is estimated from heuristic arguments related to fingerprints of chaotic dynamics of a classical counterpart of the coherently rotating complex. Validity of this estimate is confirmed numerically for the H+D2\mathrm{H}+{\mathrm{D}}_{2}H+D2​ chemical reaction. Thus we demonstrate the quantum-classical transition in temporal behavior of highly excited quantum many-body systems in the absence of external noise and coupling to an environment.
Flashing coherently rotating carbon sticks in 24^{24}24Mg+24^{24}24Mg collision
The present discussion rises a number of the questions. For example, is rotational coherence of large molecules necessarily destroyed in the conventionally statistical limit of structureless non-selective continuum (for fixed total spin and parity values) under the conditions of complete intramolecular energy redistribution and vibrational dephasing in the regime of strong ro-vibrational coupling? For the slow cross-symmetry phase relaxation, quantum coherent superpositions of a large number of complex configurations with, e.g., many different total angular momenta produce image of a rotation of macroscopic object with classically fixed (single) total angular momentum. Suppose that the quantum coherent superpositions involving a very large number of different good quantum numbers play a role, in a hidden form, in a formation of macroscopic world. Then why these quantum superpositions are so stable against quick aging/decay of ordered complex structures preventing or slowing down tendencies towards uniform occupation of the available phase space as prescribed by the random matrix theory? And what kind of complex macroscopic phenomena may reveal traces of partially coherent quantum superpositions involving a huge number of quantum-mechanically different integrals of motion behind of what is referred to as conservation laws in classical physics employed for the description of the macroscopic world?
Collisional complexes, which are formed as intermediate states in molecular collisions, are typically short-lived and decay within picoseconds. However, in ultracold collisions involving bialkali molecules, complexes can live for milliseconds, completely changing the collision dynamics. This can lead to unexpected two-body loss in samples of nonreactive molecules. During the past decade, such "sticky" collisions have been a major hindrance in the preparation of dense and stable molecular samples, especially in the quantum-degenerate regime. Currently, the behavior of the complexes is not fully understood. For example, in some cases, their lifetime has been measured to be many orders of magnitude longer than recent models predict. This is not only an intriguing problem in itself but also practically relevant, since understanding molecular complexes may help to mitigate their detrimental effects. Here, we review the recent experimental and theoretical progress in this field. We treat the case of molecule-molecule as well as molecule-atom collisions.
Thermal collisions between potassium Rydberg atoms with intermediate values of quantum number n and target molecules that capture free low-energy electrons are investigated. The velocity, binding energy, and angular distributions of heavy-Rydberg ion-pair states formed through such collisions are measured. The experimental data are analyzed with the aid of semiclassical Monte Carlo simulations to investigate the dynamics of electron attachment to a variety of target species. Multiple reaction channels involving short- and long-lived intermediates are seen for electron capture by 1,1,1-C2Cl3F3 and CBrCl3 (where dissociation of CBrCl3 intermediates involves production of Br- and Cl- ions). Electron attachment to BrCN produces long-lived BrCN-* intermediates whose dissociation results in the creation of rotationally-hot CN- anions. Electron capture by Fe(CO)5 leads to formation of Fe(CO)5-* intermediates which can fragment producing Fe(CO)4- anions, either directly or after partial redistribution of the excess energy within the intermediate has occurred. Electron transfer in Rydberg atom collisions with C2Cl4 provide no evidence of formation of long-lived C2Cl4 ions, only Cl- ions are seen. Moreover, strong Rydberg atom scattering is observed following collisions of K(12p) Rydberg states with CH3NO2. This finding is consistent with a theory which predicts that collisions between Rydberg atoms with intermediate values of n and polar molecules can lead to strong resonant quenching of Rydberg states, i.e., n and l changing, through formation of short-lived K+...CH3NO2- ion-pair states. Finally, the improvements in sensitivity to electron capture reaction dynamics that might be achieved using different Rydberg species and a crossed molecular beam are examined. Simulations are performed to demonstrate that the use of a hyperthermal helium Rydberg atomic beam and a crossed beam of target molecules such as CCl4, BrCN and CF3I can provide new insights into dissociative electron attachment reactions. The calculations show that not only can much detailed information on translational energy release distributions and intermediate lifetimes be obtained, but also on the electron radial probability density distributions in the Rydberg atoms themselves.