Intramolecular energy flow

Shirts R B and Reinhardt W P 1982 Approximate constants of motion for classically chaotic vibrational dynamics vague tori, semiclassical quantization, and classical intramolecular energy flow J. Cham. Phys. 77 5204-17... 

D. Shemesh and R. B. Gerber. Classical trajectory simulations of photoionization dynamics of tryptophan intramolecular energy flow, hydrogen-transfer processes and conformational transitions, J. Phys. Chem. A, 110 8401-8408 (2006). 

A similar restriction in intramolecular energy flow has been postulated for metalloenzyme systems [41]. In particular, in the formation of the enzyme substrate complex, the energy of binding can be trapped at the metal active site. The... 

Coulomb Force and Intramolecular Energy Flow Effects for Vibrational Energy Transfer for Small Molecules in Polar Solvents... 

Further insights into reaction dynamics can be obtained by analyzing the stability of classical trajectories. Presumably, stable periodic orbits will be restricted to KAM tori and therefore be nonreactive and unstable periodic orbits will provide information about the location of resonances and therefore some quahtative features of the intramolecular energy flow. 

The existence of bottlenecks to Hamiltonian transport suggests that intramolecular energy flow can be highly nonergodic. Thus, accounting for the bottlenecks should greatly improve chemical reaction rate theories. For example, for the 4 1 resonance shown in Figs. 2 and 3, the intramolecular bottleneck should be located at... 

Gaspard and Rice also considered a kicking field with several minima and maxima such that the mapping has several bottlenecks, with each bottleneck associated with particular fixed points. The existence of several bottlenecks allows their model to better mimic some properties of intramolecular energy flow. Specifically, they chose... 

The most important element of the Davis-Gray theory of unimolecular reaction rate is the identification of bottlenecks to intramolecular energy flow and the intermolecular separatrix to molecular fragmentation. Davis and Gray s work was motivated by the discovery of bottlenecks in chaotic transport by MacKay, Meiss, and Percival [8,9] and by Bensimon and Kadanoff [10]. 

The fact that classical unstable periodic trajectories can manifest themselves in the Wigner function implies that nonstatistical behavior in the quanmm dynamics can be intimately related to the phase-space structure of the classical molecular dynamics. Consider, for example, the bottlenecks to intramolecular energy flow. Since the intramolecular bottlenecks are caused by remnants of the most robust tori, they are presumably related to the least unstable periodic trajectories. Hence quantum scars, being most significant in the case of the least unstable periodic trajectories, are expected to be more or less connected with intramolecular bottlenecks. Indeed, this observation motivated a recent proposal [75] to semiclassically locate quantum intramolecular bottlenecks. Specifically, the most robust intramolecular bottlenecks are associated with the least unstable periodic trajectories for which Eq. (332) holds, that is,... 

In the more general case that allows for intramolecular energy flow, the effective Hamiltonian must include another perturbation term H so that... 

The effective Hamiltonian approach clearly shows the important role of intramolecular energy flow in the quantum dynamics of unimolecular dissociation. It suggests that unless intramolecular energy flow is dominantly rapid, there exist two drastically different time scales in the reaction dynamics. This is consistent with the classical concept that nonstatistical behavior in intramolecular energy flow, such as bottleneck effects, can dramatically alter the kinetics of unimolecular reaction. 

The data on Infrared photodlssoclatlon of vdW molecules provides, In principle. Information on several topics of great current Interest In addition to colllslonal resonances. One of these Is the structure of weakly bound systems. Another Is the rate of "intramolecular" energy flow from the vibration which Is initially localized within A or B Into the vdW coordinates which express the... 

Finally, we discuss the way in which these pictures of energy flow within molecules modify our expectations about unimolecular reaction rates. Both the simple pictures and approximate calculational methods discussed here, as well as the detailed calculations, are still in a very early stage of development. In the last section we mention some of the open problems facing those who wish to picture quantized intramolecular energy flow. 

The computation described above is completely classical the nuclear motion is assumed to be well described by Newton s equations. The extent to which classical mechanics provides a useful description of intramolecular energy flow is another focus of current research in this area. As one example of the validity of classical mechanics, consider the bound-state dynamics of a three-atom system confined to a line, that is. A—B—C. Computations on the case where the A—B and B—C bonds are anharmonic have been performed using both classical and quantum... 

Although we shall not deal with Hamilton-Jacobi theory here, the concept of a set of constants of the motion is vital to an understanding of the issue of intramolecular energy flow and statistical vs nonstatistical behavior. In essence, the number of global constants of the motion provides a method for grouping systems into general categories. 

To appreciate the desired description of energy flow in chemistry, recall the historical origin of the interest in intramolecular energy flow. The most prominant case is that of unimolecular decay, in which a molecule, sufficiently energized, breaks into a variety of products (e.g., ABC A -I- BC). In this case the focus of attention, and therefore of the measurement, is on the energy content of the A—B bond. This is typical of chemical descriptions in which the analysis is in terms of subunits of the molecule that are not, in themselves, naturally distinct subcomponents of the molecule. Such a description results when a zero-order basis set is used. Specifically, consider the Hamiltonian for a two-degrees-of-freedom system written, as in the classical case, in the form... 

As in the classical case, the question of the nature of intramolecular energy flow—whether it is statistical or whether it displays a specific pathway— is of interest. Unfortunately, few quantum calculations on realistic molecular systems have been performed. The example of the dynamics of benzene, initially prepared in an excited state of the C—H bond, has, however, been treated quantum mechanically. Here, the relevant zero-order Hamiltonian is of the form... 

Very few experiments providing direct information about the pathways of intramolecular energy flow in van der Waals complexes have been reported to date. In most cases studied so far, distinct channels for IVR and vibrational predissociation (VP) could not be detected separately. Among the polyatomic van der Waals complexes the cluster T Ar of s-tetrazine and argon is one of the few favourable exceptions. It exhibits several channels for... 

To focus on the question of surface effects on vibrational energy relaxation rate, without the complications of intramolecular energy flow, Benjamin and coworkers studied the vibrational relaxation of a diatomic solute molecule (single vibrational mode) at various liquid/vapor and liquid/liquid interfaces." " The solute is modeled using the Morse potential ... 

Motion for Classical Chaotic Viabrational Dynamics. Vague Tori, Semiclassical Quantitiza-tion, and Classical Intramolecular Energy Flow. 

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