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William A Goddard - One of the best experts on this subject based on the ideXlab platform.
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anisotropic shock sensitivity for β octahydro 1 3 5 7 tetranitro 1 3 5 7 tetrazocine energetic material under compressive shear loading from reaxff lg reactive dynamics simulations
Journal of Applied Physics, 2012Co-Authors: Tingting Zhou, Sergey Zybin, Yi Liu, Fenglei Huang, William A GoddardAbstract:We report here the predictions on anisotropy of shock sensitivity and of chemical process initiation in single crystal β-octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (β-HMX) using compressive shear reactive dynamics (CS-RD) model with ReaxFF-lg reactive Force Field. Analysis of resolved shear stress induced by uniaxial compression along three shock directions normal to (110), (011), and (010) planes leads to identify eight slip systems as candidates for shear deformation. For each of the eight slip systems, non-equilibrium reactive dynamics simulations were carried out to determine thermal, mechanical, and chemical responses to shear deformation. Shock direction normal to (010) plane exhibits large shear stress barriers arising from steric hindrance between molecules of adjacent layers leading to local dramatic energy and temperature increases under shear flow that in turn accelerate chemical bond breaking and initial product formation processes, promoting further molecular decomposition and eventually transition to detonation. This suggests that single crystal β-HMX is sensitive to shocks in direction normal to (010) plane. Shock directions normal to (110) and (011) planes reveal significantly less steric hindrance, leading to more modest energy and temperature increases followed by slower chemical reaction initiation. Thus, shock directions normal to (110) and (011) planes are less sensitive than shock direction normal to (010) plane, which agree with interpretations from currently available plate impact experiments on HMX. This validation of CS-RD and ReaxFF for characterizing sensitivity of single crystal energetic materials indicates that these methods can be applied to study sensitivity for more complex polymer bonded explosives and solid composite propellants having complex microstructures, corrugated interfaces, as well as defects.
Tingting Zhou - One of the best experts on this subject based on the ideXlab platform.
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anisotropic shock sensitivity for β octahydro 1 3 5 7 tetranitro 1 3 5 7 tetrazocine energetic material under compressive shear loading from reaxff lg reactive dynamics simulations
Journal of Applied Physics, 2012Co-Authors: Tingting Zhou, Sergey Zybin, Yi Liu, Fenglei Huang, William A GoddardAbstract:We report here the predictions on anisotropy of shock sensitivity and of chemical process initiation in single crystal β-octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (β-HMX) using compressive shear reactive dynamics (CS-RD) model with ReaxFF-lg reactive Force Field. Analysis of resolved shear stress induced by uniaxial compression along three shock directions normal to (110), (011), and (010) planes leads to identify eight slip systems as candidates for shear deformation. For each of the eight slip systems, non-equilibrium reactive dynamics simulations were carried out to determine thermal, mechanical, and chemical responses to shear deformation. Shock direction normal to (010) plane exhibits large shear stress barriers arising from steric hindrance between molecules of adjacent layers leading to local dramatic energy and temperature increases under shear flow that in turn accelerate chemical bond breaking and initial product formation processes, promoting further molecular decomposition and eventually transition to detonation. This suggests that single crystal β-HMX is sensitive to shocks in direction normal to (010) plane. Shock directions normal to (110) and (011) planes reveal significantly less steric hindrance, leading to more modest energy and temperature increases followed by slower chemical reaction initiation. Thus, shock directions normal to (110) and (011) planes are less sensitive than shock direction normal to (010) plane, which agree with interpretations from currently available plate impact experiments on HMX. This validation of CS-RD and ReaxFF for characterizing sensitivity of single crystal energetic materials indicates that these methods can be applied to study sensitivity for more complex polymer bonded explosives and solid composite propellants having complex microstructures, corrugated interfaces, as well as defects.
Peter B Kelly - One of the best experts on this subject based on the ideXlab platform.
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resonance raman spectrum of the allyl d5 radical and the Force Field Analysis of the allyl radical
Journal of Chemical Physics, 1993Co-Authors: Xianming Liu, James D Getty, Peter B KellyAbstract:Resonance Raman spectra of the allyl‐d5 radical have been obtained with excitation between 247 and 223 nm. Analysis of the spectra yields the first observation of fundamental frequencies, ν4, ν5, and ν7 and overtone frequencies 2ν9, 2ν10, and 2ν12. The new vibrational data are combined with previously observed frequencies of allyl‐h5 and allyl‐d5 radical to produce the Force Field Analysis for the allyl radical. This study suggests reassignment of several previously observed infrared (IR) bands. Experimental frequencies and assignments for allyl‐h5 and allyl‐d5 are compared with results from ab initio calculations. Force constants obtained in the present work are compared with the Force constants of other sp2 hybridization molecules such as benzene, allene, and ethylene.
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a Force Field Analysis of the methyl radical x 2a 2 state stretching potential using the local mode coupled morse oscillator model
Journal of Chemical Physics, 1991Co-Authors: S G Westre, Xianming Liu, James D Getty, Peter B KellyAbstract:The local mode‐coupled Morse oscillator model was utilized to determine the quadratic, cubic, and quartic Force constants for the vibrational stretching potential energy functions of the CH3, CD3, CH2D, and CHD2 using stretching fundamentals and overtones derived from resonance Raman studies. The Morse harmonic frequency and anharmonic constant of the methyl radical indicate that bonding in the methyl radical and a variety of ethylenic molecules is primarily a function of the sp2 hybridization of the central atom and that the bonding is not extensively influenced by the methyl radical’s unpaired electron or the π bonding in the ethylenic molecules. The vibrational states of the methyl radical are best described by wave functions containing significant amounts of normal mode character. The stretching frequencies for the tritiated methyl radical isotopomers are calculated.
Antonin Vlcek - One of the best experts on this subject based on the ideXlab platform.
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ground and electronically excited states of cr co 4 bipyridine energy factored Force Field Analysis of co stretching vibrations and resonance raman study
Inorganica Chimica Acta, 1998Co-Authors: Antonin Vlcek, Friedrichwilhelm Grevels, Theo L Snoeck, D J StufkensAbstract:Abstract IR spectra of Cr(CO) 4 (bipyridine) and its 13 CO-containing isotopomers were used to calculate all the stretching and interaction CO Force constants and the normal coordinates of the CO stretching vibrations. Resonance Raman (rR) spectra of Cr(CO) 4 (bpy) were measured and compared with the Fourier transform Raman spectra. The most resonance enhanced Raman bands belongs to the ring-deformation vibrations of the bpy ligand and the A 1 ν(CO) vibration at 2004 cm −1 . The rR spectral pattern confirms a localized Cr → bpy metal-to-ligand charge transfer (MLCT) character of the electronic transition responsible for the visible absorption band. It is shown that the MLCT excitation also affects the bonding within the Cr(CO) 4 molety. Of the two A 1 ν(CO) vibrations, only the one at higher frequency (A 1 2 , 2004 cm −1 ) gives rise to a resonance enhanced Raman band. Analysis of this effect, based on the energy factored Force Field (EFFF) calculated normal coordinates of both symmetric ν(CO) vibrations, shows that the MLCT excitation affects the CO bonds in both the axial and equatorial CO ligands, the influence on the axial ligands being larger. The Raman band due to the A 1 1 symmetric ν(CO)_vibration is not resonance enhanced because of an out-of-phase coupling between the symmetric vibrations of the axial and equatorial pairs of CO ligands. Raman bands due to CrC stretching and CrCO bending vibrations, apparently coupled with the vibrations of the Cr(bpy) moiety, were identified by the 13 CO isotope effect and found to be resonance enhanced.
Stephen J Lippard - One of the best experts on this subject based on the ideXlab platform.
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characterization of a synthetic peroxodiiron iii protein model complex by nuclear resonance vibrational spectroscopy
Chemical Communications, 2011Co-Authors: Loi H Do, Hongxin Wang, Yoshitaka Yoda, Christine E Tinberg, Stephen P Cramer, Eric Dowty, Stephen J LippardAbstract:The vibrational spectrum of an η1,η1-1,2-peroxodiiron(III) complex was measured by nuclear resonance vibrational spectroscopy and fit using an empirical Force Field Analysis. Isotopic 18O2 labelling studies revealed a feature involving motion of the {Fe2(O2)}4+ core that was not previously observed by resonance Raman spectroscopy.