ORCID Profile
0000-0001-5703-551X
Current Organisation
University of Melbourne
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Publisher: American Chemical Society (ACS)
Date: 17-03-2015
DOI: 10.1021/JP510995Z
Abstract: Decomposition of energetic salts TKX-50 and MAD-X1 (dihydroxylammonium 5,5'-bistetrazole-1,1'-diolate and dihydroxylammonium 3,3'-dinitro-5,5'-bis-1,2,4-triazole-1,1'-diol, respectively), following electronic state excitation, is investigated both experimentally and theoretically. The NO and N2 molecules are observed as initial decomposition products from the two materials subsequent to UV excitation. Observed NO products are rotationally cold ( 1500 K). The vibrational temperature of the NO product from TKX-50 is (2600 ± 250) K, (1100 ± 250) K hotter than that produced from MAD-X1. Observed N2 products of these two species are both rotationally cold (<30 K). Initial decomposition mechanisms for these two electronically excited salts are explored at the complete active space self-consistent field (CASSCF) level. Potential energy surface calculations at the CASSCF(8,8)/6-31G(d) level illustrate that conical intersections play an essential role in the decomposition mechanisms. Electronically excited S1 molecules can nonadiabatically relax to the lower electronic state through (S1/S0)CI conical intersections. Both TKX-50 and MAD-X1 have two (S1/S0)CI conical intersections between S1 and S0 states, related to and leading to two different reaction paths, forming N2 and NO products. N2 products are released by the opening of the tetrazole or triazole rings of TKX-50 and MAD-X1. NO products are released from the amine N-oxide moiety of TKX-50, and for MAD-X1, they are produced through nitro-nitrite isomerizations. The observed rotational energy distributions for NO and N2 products are consistent with the final structures of the respective transition states for each molecule on its S0 potential energy surface.
Publisher: AIP Publishing
Date: 15-06-2016
DOI: 10.1063/1.4953552
Abstract: Unimolecular decomposition of nitrogen-rich energetic molecules 1,2-bis(1H-tetrazol-1-yl)ethane (1-DTE), 1,2-bis(1H-tetrazol-5-yl)ethane (5-DET), N,N-bis(1H-tetrazol-5-yl)amine (BTA), and 5,5’-bis(tetrazolyl)hydrazine (BTH) has been explored via 283 nm two photon laser excitation. The maximum absorption wavelength in the UV-vis spectra of all four materials is around 186–222 nm. The N2 molecule, with a cold rotational temperature (& K), is observed as an initial decomposition product from the four molecules, subsequent to UV excitation. Initial decomposition mechanisms for these four electronically excited isolated molecules are explored at the complete active space self-consistent field (CASSCF) level. Potential energy surface calculations at the CASSCF(12,8)/6-31G(d) level illustrate that conical intersections play an essential role in the decomposition mechanism. The tetrazole ring opens on the S1 excited state and through conical intersections (S1/S0)CI, N2 product is formed on the ground state potential energy surface without rotational excitation. The tetrazole rings of all four energetic molecules open at the N1—N2 ring bond with the lowest energy barrier: the C—N bond opening has higher energy barrier than that for any of the N—N ring bonds. Therefore, the tetrazole rings open at their N—N bonds to release N2. The vibrational temperatures of N2 product from all four energetic materials are hot based on theoretical calculations. The different groups (CH2—CH2, NH—NH, and NH) joining the tetrazole rings can cause apparent differences in explosive behavior of 1-DTE, 5-DTE, BTA, and BTH. Conical intersections, non-Born-Oppenheimer interactions, and dynamics are the key features for excited electronic state chemistry of organic molecules, in general, and energetic molecules, in particular.
Publisher: Informa UK Limited
Date: 05-2009
DOI: 10.4161/PSB.4.5.8542
Publisher: AIP Publishing
Date: 12-2017
DOI: 10.1063/1.5011773
Abstract: We calculated the photoinduced decomposition of various nitrotoluene molecules, resulting in the formation of atomic carbon, at the B3LYP/6-311++G(d,p) level of theory using Gaussian 09. In addition, we used TD-DFT (B3LYP/6-311++G(d,p)) to calculate the excitation energies. The results confirm our previously reported experimental results. Specifically, we show that the absorption of 226 nm (5.49 eV) light can lead to the decomposition of nitrotoluene molecules and the formation of atomic carbon. One 226 nm photon is sufficient for the dissociation of carbon from 2-NT and 4-NT molecules. During the dissociation process, the CH3 group provides the dissociated carbon atom and the NO2 group accepts the H atoms from either the CH3 group or the benzene ring before carbon exits the molecular system. For the second and third carbon dissociation of 2-NT, the energy barriers are 6.70 eV and 7.43 eV, respectively, and two 226 nm photons would need to be absorbed by the molecule. If extra NO is present during the first carbon dissociation of 2-NT, it gets involved in the last two decomposition steps and forms a C=NH-N=O structure which stabilizes the decomposition products and lowers the energy barrier from 5.22 eV to 4.70 eV. However, for the second and third carbon dissociation of 2-NT, the NO molecules have no apparent effect. For nitrotoluene molecules with two or three NO2 groups (i.e., 2,4-DNT, 2,6-DNT, 3,4-DNT, and 2,4,6-TNT), the first carbon dissociation energies are between 5.26 eV and 5.57 eV. The carbon dissociation pathways for these molecules are similar to those of 2-NT. In 2,4-DNT, the lowest energy barriers for the second and third carbon dissociation are 6.54 eV and 6.60 eV, respectively, which are about 1 eV higher than the energy barrier for the first carbon dissociation. In case of 2,4-DNT/NO and 2,4,6-TNT/NO, NO acts as a catalyst in the first carbon dissociation processes and forms a C=NH-N=O structure which lowers the energy barriers by 0.48 eV and 0.89 eV, respectively.
Publisher: AIP Publishing
Date: 19-02-2014
DOI: 10.1063/1.4865266
Abstract: Decomposition of the energetic material FOX-7 (1,1-diamino-2,2-dinitroethylene, C2H4N4O4) is investigated both theoretically and experimentally. The NO molecule is observed as an initial decomposition product subsequent to electronic excitation. The observed NO product is rotationally cold (& K) and vibrationally hot (2800 K). The initial decomposition mechanism is explored at the complete active space self-consistent field (CASSCF) level. Potential energy surface calculations at the CASSCF(12,8)/6-31G(d) level illustrate that conical intersections play an essential role in the decomposition mechanism. Electronically excited S2 FOX-7 can radiationlessly relax to lower electronic states through (S2/S1)CI and (S1/S0)CI conical intersections and undergo a nitro-nitrite isomerization to generate NO product on the S0 state. The theoretically predicted mechanism is consistent with the experimental results. As FOX-7 decomposes on the ground electronic state, thus, the vibrational energy of the NO product from FOX-7 is high. The observed rotational energy distribution for NO is consistent with the final transition state structure on the S0 state. Ground state FOX-7 decomposition agrees with previous work: the nitro-nitrite isomerization has the lowest average energy barrier, the C–NH2 bond cleavage is unlikely under the given excitation conditions, and HONO formation on the ground state surface is energy accessible but not the main process.
Publisher: Oxford University Press (OUP)
Date: 15-02-2012
DOI: 10.1093/JXB/ERS026
Publisher: AIP Publishing
Date: 21-01-2014
DOI: 10.1063/1.4861670
Abstract: Decomposition of energetic material 3,4-dinitropyrazole (DNP) and two model molecules 4-nitropyrazole and 1-nitropyrazole is investigated both theoretically and experimentally. The initial decomposition mechanisms for these three nitropyrazoles are explored with complete active space self-consistent field (CASSCF) level. The NO molecule is observed as an initial decomposition product from all three materials subsequent to UV excitation. Observed NO products are rotationally cold (<50 K) for all three systems. The vibrational temperature of the NO product from DNP is (3850 ± 50) K, 1350 K hotter than that of the two model species. Potential energy surface calculations at the CASSCF(12,8)/6-31+G(d) level illustrate that conical intersections plays an essential role in the decomposition mechanism. Electronically excited S2 nitropyraozles can nonradiatively relax to lower electronic states through (S2/S1)CI and (S1/S0)CI conical intersection and undergo a nitro-nitrite isomerization to generate NO product either in the S1 state or S0 state. In model systems, NO is generated in the S1 state, while in the energetic material DNP, NO is produced on the ground state surface, as the S1 decomposition pathway is energetically unavailable. The theoretically predicted mechanism is consistent with the experimental results, as DNP decomposes in a lower electronic state than do the model systems and thus the vibrational energy in the NO product from DNP should be hotter than from the model systems. The observed rotational energy distributions for NO are consistent with the final structures of the respective transition states for each molecule.
Publisher: Oxford University Press (OUP)
Date: 26-02-2009
DOI: 10.1093/JXB/ERP026
Publisher: American Chemical Society (ACS)
Date: 07-06-2022
Abstract: The rate of oxidative damage of aliphatic amino acids and dipeptides by the environmental pollutant nitrate radical (NO
Publisher: AIP Publishing
Date: 10-08-2016
DOI: 10.1063/1.4960345
Abstract: Unimolecular decomposition of nitrogen-rich energetic salt molecules bis(ammonium)5,5′-bistetrazolate (NH4)2BT and bis(triaminoguanidinium) 5,5′-azotetrazolate TAGzT, has been explored via 283 nm laser excitation. The N2 molecule, with a cold rotational temperature (& K), is observed as an initial decomposition product, subsequent to UV excitation. Initial decomposition mechanisms for the two electronically excited salt molecules are explored at the complete active space self-consistent field (CASSCF) level. Potential energy surface calculations at the CASSCF(12,8)/6-31G(d) ((NH4)2BT) and ONIOM (CASSCF/6-31G(d):UFF) (TAGzT) levels illustrate that conical intersections play an essential role in the decomposition mechanism as they provide non-adiabatic, ultrafast radiationless internal conversion between upper and lower electronic states. The tetrazole ring opens on the S1 excited state surface and, through conical intersections (S1/S0)CI, N2 product is formed on the ground state potential energy surface without rotational excitation. The tetrazole rings open at the N2—N3 ring bond with the lowest energy barrier: the C—N ring bond opening has a higher energy barrier than that for any of the N—N ring bonds: this is consistent with findings for other nitrogen-rich neutral organic energetic materials. TAGzT can produce N2 either by the opening of tetrazole ring or from the N=N group linking its two tetrazole rings. Nonetheless, opening of a tetrazole ring has a much lower energy barrier. Vibrational temperatures of N2 products are hot based on theoretical predictions. Energy barriers for opening of the tetrazole ring for all the nitrogen-rich energetic materials studied thus far, including both neutral organic molecules and salts, are in the range from 0.31 to 2.71 eV. Energy of the final molecular structure of these systems with dissociated N2 product is in the range from −1.86 to 3.11 eV. The main difference between energetic salts and neutral nitrogen-rich energetic material is that energetic salts usually have lower excitation energy.
Publisher: American Chemical Society (ACS)
Date: 18-09-2012
DOI: 10.1021/JP305936F
Abstract: The independent molecule and ion temperature dependence of the rate coefficient for the H(3)O(+) and (C(2)H(2))(2) reaction producing C(2)H(5)O(+) are determined using a coaxial molecular beam radio frequency ring electrode ion trap (CoMB-RET). The H(3)O(+) temperature is varied from 25 to 170 K, while the equilibrated C(2)H(2)/(C(2)H(2))(2) beam temperatures s led are 160, 180, 200, and 220 K. The rate coefficient of the H(3)O(+) + (C(2)H(2))(2) reaction is determined to be 4.0 × 10(-10) × (T(react)/300)(-2.5) in the reaction temperature range of T(react) = 114-187 K. The H(3)O(+) and C(2)H(2) radiative association reaction is found to have a rate coefficient below 1 × 10(-13) cm(3)·s(-1) at 187 K. This result is consistent with Herbst's experimental determination.
Publisher: AIP Publishing
Date: 28-03-2015
DOI: 10.1063/1.4916111
Abstract: Decomposition of nitrogen-rich energetic materials 1,5′-BT, 5,5′-BT, and AzTT (1,5′-Bistetrazole, 5,5′-Bistetrazole, and 5-(5-azido-(1 or 4)H-1,2,4-triazol-3-yl)tetrazole, respectively), following electronic state excitation, is investigated both experimentally and theoretically. The N2 molecule is observed as an initial decomposition product from the three materials, subsequent to UV excitation, with a cold rotational temperature (& K). Initial decomposition mechanisms for these three electronically excited materials are explored at the complete active space self-consistent field (CASSCF) level. Potential energy surface calculations at the CASSCF(12,8)/6-31G(d) level illustrate that conical intersections play an essential role in the decomposition mechanism. Electronically excited S1 molecules can non-adiabatically relax to their ground electronic states through (S1/S0)CI conical intersections. 1,5′-BT and 5,5′-BT materials have several (S1/S0)CI conical intersections between S1 and S0 states, related to different tetrazole ring opening positions, all of which lead to N2 product formation. The N2 product for AzTT is formed primarily by N–N bond rupture of the –N3 group. The observed rotational energy distributions for the N2 products are consistent with the final structures of the respective transition states for each molecule on its S0 potential energy surface. The theoretically derived vibrational temperature of the N2 product is high, which is similar to that found for energetic salts and molecules studied previously.
Publisher: AIP Publishing
Date: 14-04-2016
DOI: 10.1063/1.4945624
Abstract: A 118 nm laser is employed as a high energy, single photon (10.51 eV hoton) source for study of the dynamics and fragmentation of the ammonia borane (NH3BH3) cation and its cluster ions through time of flight mass spectrometry. The behavior of ammonia ion and its cluster ions is also investigated under identical conditions in order to explicate the ammonia borane results. Charge distributions, molecular orbitals, and spin densities for (NH3BH3)n and its cations are explored at both the second-order perturbation theory (MP2) and complete active space self-consistent field (CASSCF) theory levels. Initial dissociation mechanisms and potential energy surfaces for ionized NH3BH3, NH3, and their clusters are calculated at the MP2/6-311++G(d,p) level. Protonated clusters (NH3)xH+ dominate ammonia cluster mass spectra: our calculations show that formation of (NH3)n−1H+ and NH2 from the nascent (NH3)n+ has the lowest energy barrier for the system. The only common features for the (NH3)n+ and (NH3BH3)n+ mass spectra under these conditions are found to be NHy+ (y = 0,…,4) at m/z = 14–18. Molecular ions with both 11B and 10B isotopes are observed, and therefore, product ions observed for the (NH3BH3)n cluster system derive from (NH3BH3)n clusters themselves, not from the NH3 moiety of NH3BH3 alone. NH3BH2+ is the most abundant ionization product in the (NH3BH3)n+ cluster spectra: calculations support that for NH3BH3+, an H atom is lost from the BH3 moiety with an energy barrier of 0.67 eV. For (NH3BH3)2+ and (NH3BH3)3+ clusters, a Bδ+⋯Hδ−⋯δ−H⋯δ+B bond can form in the respective cluster ions, generating a lower energy, more stable ion structure. The first step in the (NH3BH3)n+ (n = 2, 3) dissociation is the breaking of the Bδ+⋯Hδ−⋯δ−H⋯δ+B moiety, leading to the subsequent release of H2 from the latter cluster ion. The overall reaction mechanisms calculated are best represented and understood employing a CASSCF natural bond orbital description of the valence electron distribution for the various clusters and monomers. Comparison of the present results with those found for solid NH3BH3 suggests that NH3BH3 can be a good hydrogen storage material.
Publisher: American Chemical Society (ACS)
Date: 13-12-2011
DOI: 10.1021/JP105850B
Abstract: The neutral molecule temperature dependence of the rate coefficient for the electron transfer reaction from H(2)O to N(2)(+) is determined using a coaxial molecular beam radio frequency ring electrode ion trap (CoMB-RET) method. The temperature of the N(2)(+) ions was maintained at 100 K, while the effusive water beam temperature was varied from 300 to 450 K. The result demonstrates the neutral molecule rotational/translational energy dependence on the rate coefficient of an ion-dipolar molecule reaction. It is found that the rate coefficient in the above temperature range follows the prediction of the simplest ion-dipole capture model. Use of different buffer gas collisional cooling in both the ion source and the RET reveals the effects of both translational and vibrational energy of the N(2)(+) ions.
Publisher: American Chemical Society (ACS)
Date: 16-11-2012
DOI: 10.1021/JP306372V
Abstract: The rate coefficients for the forward and reverse proton-transfer reactions C(2)H(4) + H(3)O(+) ⇄ C(2)H(5)(+) + H(2)O are studied with respect to independent varied neutral molecule and ion temperatures. The measurements are performed using a coaxial molecular beam radio frequency ring electrode ion trap at trap temperatures down to 23 K and beam temperatures up to 450 K. The temperature-dependent rate coefficients suggest that in this temperature window, the reaction proceeds through a statistically equilibrated complex. In order to explain the observed rate coefficients, a new type of reaction temperature was defined in these studies that considered collisional and internal (rotational and vibrational) degrees of freedom of both H(3)O(+) and C(2)H(4). The enthalpy and entropy of the equilibrium reaction deduced from a Van't Hoff plot are ΔH = (5.1 ± 0.5) kJ·mol(-1) and ΔS = (-15.0 ± 0.9) J·mol(-1)·K(-1), respectively.
Publisher: Elsevier BV
Date: 2019
Publisher: AIP Publishing
Date: 03-01-2017
DOI: 10.1063/1.4972259
Abstract: Unimolecular decomposition of energetic molecules, 3,3′-diamino-4,4′-bisfuroxan (labeled as A) and 4,4′-diamino-3,3′-bisfuroxan (labeled as B), has been explored via 226/236 nm single photon laser excitation/decomposition. These two energetic molecules, subsequent to UV excitation, create NO as an initial decomposition product at the nanosecond excitation energies (5.0–5.5 eV) with warm vibrational temperature (1170 ± 50 K for A, 1400 ± 50 K for B) and cold rotational temperature (& K). Initial decomposition mechanisms for these two electronically excited, isolated molecules are explored at the complete active space self-consistent field (CASSCF(12,12)/6-31G(d)) level with and without MP2 correction. Potential energy surface calculations illustrate that conical intersections play an essential role in the calculated decomposition mechanisms. Based on experimental observations and theoretical calculations, NO product is released through opening of the furoxan ring: ring opening can occur either on the S1 excited or S0 ground electronic state. The reaction path with the lowest energetic barrier is that for which the furoxan ring opens on the S1 state via the breaking of the N1—O1 bond. Subsequently, the molecule moves to the ground S0 state through related ring-opening conical intersections, and an NO product is formed on the ground state surface with little rotational excitation at the last NO dissociation step. For the ground state ring opening decomposition mechanism, the N—O bond and C—N bond break together in order to generate dissociated NO. With the MP2 correction for the CASSCF(12,12) surface, the potential energies of molecules with dissociated NO product are in the range from 2.04 to 3.14 eV, close to the theoretical result for the density functional theory (B3LYP) and MP2 methods. The CASMP2(12,12) corrected approach is essential in order to obtain a reasonable potential energy surface that corresponds to the observed decomposition behavior of these molecules. Apparently, highly excited states are essential for an accurate representation of the kinetics and dynamics of excited state decomposition of both of these bisfuroxan energetic molecules. The experimental vibrational temperatures of NO products of A and B are about 800–1000 K lower than previously studied energetic molecules with NO as a decomposition product.
Location: United States of America
No related grants have been discovered for Bing Yuan.