Vibrational energy transfer in shocked molecular crystals

Hooper, Joseph P.

doi:10.1063/1.3273212

Cited by 28 publications

(39 citation statements)

References 47 publications

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“…III, were performed for spatially resolved regions containing contiguous molecular layers (e.g., ignoring minus signs, layers 1-2, 1-10, 61-80, etc.). Immediately behind the shock front the five two-layer-thick regions (again, ignoring minus signs) 1-2, 3-4, 5-6, 7-8, and 9-10 were used to define a ten-layer-thick one (1)(2)(3)(4)(5)(6)(7)(8)(9)(10). Throughout the analysis we considered only layers −1 to −220 behind the shock front and layers +1 to +20 ahead of the shock front.…”

Section: Of Ref 3 For An Illustration Of the Simulation Cellmentioning

confidence: 99%

“…[5][6][7][8] The large anisotropic strains and high strain rates imposed by shock wave passage through a crystal result in molecules containing relatively large amounts of energy that is, in general, non-thermally distributed immediately behind the shock front. Phonon and molecular modes that are close to mechanical resonances with the shock wave are preferentially excited, after which redistribution of the shock excitation energy to the remaining modes of the system occurs; this mechanism is widely accepted 9,10 and has come to be known as vibrational multi-phonon up-pumping. 11,12 Particularly in the case of strong, narrow shock waves, it is possible that the kinetic energies in the subset of modes initially excited by the shock are not Maxwell-Boltzmann distributed.…”

Section: Introductionmentioning

confidence: 99%

“…Hooper 10 has recently presented a theory for relaxation of crystals following shocks based on basic theory of energy relaxation. He gives a comprehensive, but terse, review of the theories that have been advanced for the relaxation of shocked materials.…”

Section: Introductionmentioning

confidence: 99%

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Post-shock relaxation in crystalline nitromethane

Rivera‐Rivera

Sewell

Thompson

2013

The Journal of Chemical Physics

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Molecular dynamics simulations of shocked (100)-oriented crystalline nitromethane were carried out to determine the rates of relaxation behind the shock wave. The forces were described by the fully flexible non-reactive Sorescu-Rice-Thompson force field [D. C. Sorescu, B. M. Rice, and D. L. Thompson, J. Phys. Chem. B 104, 8406 (2000)]. The time scales for local and overall thermal equilibration in the shocked crystal were determined. The molecular center-of-mass and atomic kinetic energy distributions rapidly reach substantially different local temperatures. Several picoseconds are required for the two distributions to converge, corresponding to establishment of thermal equilibrium in the shocked crystal. The decrease of the molecular center-of-mass temperature and the increase of the atomic temperature behind the shock front exhibit essentially exponential dependence on time. Analysis of covalent bond distance distributions ahead of, immediately behind, and well behind the shock front showed that the effective bond stretching potentials are essentially harmonic. Effective force constants for the C-N, C-H, and N-O bonds immediately behind the shock front are larger by factors of 1.6, 2.5, and 2.0, respectively, than in the unshocked crystal; and by factors of 1.2, 2.2, and 1.7, respectively, compared to material sufficiently far behind the shock front to be essentially at thermal equilibrium.

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Section: Of Ref 3 For An Illustration Of the Simulation Cellmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Post-shock relaxation in crystalline nitromethane

Rivera‐Rivera

Sewell

Thompson

2013

The Journal of Chemical Physics

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“…Additional support for the elastic spring model comes from shockwave studies (31)(32)(33)(34)(35). In an experiment by Dlott and coworkers, a 50-µm-thick aluminum plate hits a solid polymer target with a velocity of 1 km/s (35).…”

Section: Q Reversibly Deposits Energy In the Scatterermentioning

confidence: 99%

The role of momentum transfer during incoherent neutron scattering is explained by the energy landscape model

Frauenfelder

Young

Fenimore

2017

Proc. Natl. Acad. Sci. U.S.A.

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We recently introduced a model of incoherent quasielastic neutron scattering (QENS) that treats the neutrons as wave packets of finite length and the protein as a random walker in the free energy landscape. We call the model ELM for "energy landscape model." In ELM, the interaction of the wave packet with a proton in a protein provides the dynamic information. During the scattering event, the momentum Q(t) is transferred by the wave packet to the struck proton and its moiety, exerting the force F(t) = dQ(t)/dt. The resultant energy E is stored elastically and returned to the neutron as it exits. The energy is given by E = k B (T 0 + χQ), where T 0 is the ambient temperature and χ (≈ 91 KÅ) is a new elastobaric coefficient. Experiments yield the scattering intensity (dynamic structure factor) S(Q; T) as a function of Q and T. To test our model, we use published data on proteins where only thermal vibrations are active. ELM competes with the currently accepted theory, here called the spatial motion model (SMM), which explains S(Q, T) by motions in real space. ELM is superior to SMM: It can explain the experimental angular and temperature dependence, whereas SMM cannot do so.QENS | de Broglie neutron wave packet | pressure-temperature equivalence | transient energy transfer I ncoherent quasielastic neutron scattering (QENS) is used to study, for instance, the dynamics of complex systems (1, 2). In these experiments, the scattering intensity S (Q, ω, T ) is measured as function of temperature T , momentum transfer Q, and energy transfer ω. "Incoherent" essentially means that the neutron scatters from only one proton, and thus interference from different protons does not contribute. To extract the information from the data, a model is needed. The currently accepted model, used for > 50 y, assumes that the observed effects are due to spatial motions. We call it the spatial motion model (SMM). We recently introduced a model in which S (Q, ω, T ) is based on motions in the conformational free energy landscape (FEL) (3, 4). We call the model ELM, for energy landscape model. ELM assumes that the effects observed in QENS are predominantly due to changes in the population of the FEL. ELM as introduced in ref. 4 explained the neutron scattering from proteins, but left the role of the momentum transfer Q in limbo. The Q dependence is noteworthy because, although the physics of n-p scattering at low energies is s-wave (isotropic), the observed scattering from proteins is Q-dependent (see Fig. 3A), meaning anisotropic. We have now found that Q plays an important role: It creates an inhomogeneity in the target during the passage of the neutron.Consider a neutron with wave vector q that hits a proton in a protein. S (Q, ω, T ) is measured as a function of the temperature T at different scattering angles, characterized by their wave vectors q . The wave vectors q and q determine the transferred wave vector, Q = q − q. Q is related to the momentum by P = Q. E = ω is the energy change of the neutron when it has completed its scatter...

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“…The shock compression of condensed matter may lead to chemical reactions through the generation of high temperatures, high pressures [1], and transient non-equilibrium phenomena [2]. The reaction pathways accessed by shock compression are difficult to track experimentally owing to the inherently short time scales and the rapid onset of optical opacity.…”

Section: Introductionmentioning

confidence: 99%

Self-consistent tight-binding molecular dynamics simulations of shock-induced reactions in hydrocarbons

Cawkwell

Sanville

Mniszewski

et al. 2012

AIP Conference Proceedings

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Abstract.A series of reactive molecular dynamics (MD) simulations of the shock compression of liquid ethane and ethene have been performed using a self-consistent tight-binding (SC-TB) model for hydrocarbons. We employ a recursive purification algorithm for the computation of the density matrix that enables a rapid evaluation of interatomic forces using dense matrix algebra on graphics processing units (GPUs) or sparse matrix algebra for O(N) performance. We achieve a precise long-term conservation of the total energy during microcanonical MD by propagating self-consistently calculated quantities using the extended Lagrangian Born-Oppenheimer MD scheme. No shock-induced reactions were observed during our simulations of liquid ethane, but liquid ethene underwent radical chain polymerization reactions under relatively weak shocks.

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Vibrational energy transfer in shocked molecular crystals

Cited by 28 publications

References 47 publications

Post-shock relaxation in crystalline nitromethane

Post-shock relaxation in crystalline nitromethane

The role of momentum transfer during incoherent neutron scattering is explained by the energy landscape model

Self-consistent tight-binding molecular dynamics simulations of shock-induced reactions in hydrocarbons

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