| 1. |
- Yaempongsa, Dhebbajaj, Professor, et al.
(författare)
-
Improving the Stability of Trinitramide by Chemical Substitution : N(NF2)(3) has Higher Stability and Excellent Propulsion Performance
- 2021
-
Ingår i: Propellants, explosives, pyrotechnics. - : Wiley. - 0721-3115 .- 1521-4087. ; 46:2, s. 245-252
-
Tidskriftsartikel (refereegranskat)abstract
- The potential for improving the stability of trinitramide (N(NO2)(3)) by chemical substitution of the NO2 group has been investigated using Kohn-Sham density functional theory [M06-2X/6-31+G(d,p)] and ab initio quantum chemistry [CBS-QB3]. Monosubstituted analogs are generally found to have a decreased N-NO2 bond dissociation enthalpy (BDE) because of increased stabilization of the N(NO2)X radical intermediate resulting from the bond cleavage. This is particularly apparent for N(NO2)(2)NH2, which has a BDE of only 54 kJ/mol. Instead it is shown that the stability of TNA can be significantly improved by substituting all three NO2 for the NF2 group. The resulting molecule, N(NF2)(3), has a N-N BDE of 138 kJ/mol, which is 17 kJ/mol higher than the N-N BDE of N(NO2)(3). In contrast to N(NO2)(3), there are no indications that the stability of N(NF2)(3) is significantly reduced in polar solvents. Condensed phase properties of N(NF2)(3) have been estimated based on surface electrostatic potential calculations, and N(NF2)(3) is estimated to be a liquid in the approximate temperature range of 170-290 K because of its nonpolar character. The performance of N(NF2)(3) in propellant formulations with fuels rich in hydrogen and/or aluminum has been investigated. N(NF2)(3) propellants are shown to outperform propellants based on standard oxidizers by up to 20 % in specific impulse and up to 100 % in density impulse. Compositions of N(NF2)(3) and HMX have significantly higher detonation performance than CL-20.
|
|
| 2. |
- Andrae, Johan C. G., et al.
(författare)
-
HCCI experiments with toluene reference fuels modeled by a semidetailed chemical kinetic model
- 2008
-
Ingår i: Combustion and Flame. - : Elsevier BV. - 0010-2180 .- 1556-2921. ; 155:4, s. 696-712
-
Tidskriftsartikel (refereegranskat)abstract
- A semidetailed mechanism (137 species and 633 reactions) and new experiments in a homogeneous charge conic pression ignition (HCCI) engine on the autoignition of toluene reference fuels are presented. Skeletal mechanisms for isooctane and n-heptane were added to a detailed toluene submechanism. The model shows generally good agreement with ignition delay times measured in a shock tube and a rapid compression machine and is sensitive to changes in temperature, pressure, and mixture strength. The addition of reactions involving the formation and destruction of benzylperoxide radical was crucial to modeling toluene shock tube data. Laminar burning velocities for benzene and toluene were well predicted by the model after some revision of the high-temperature chemistry. Moreover, laminar burning velocities of a real gasoline at 353 and 500 K Could be predicted by the model using a toluene reference fuel as a surrogate. The model also captures the experimentally observed differences in combustion phasing of toluene/n-heptane mixtures, compared to a primary reference fuel of the same research octane number, in HCCI engines as the intake pressure and temperature are changed. For high intake pressures and low intake temperatures, a sensitivity analysis at the moment of maximum heat release rate shows that the consumption of phenoxy radicals is rate-limiting when a toluene/n-heptane fuel is used, which makes this fuel more resistant to autoignition than the primary reference fuel. Typical CPU times encountered in zero-dimensional calculations were on the order of seconds and minutes in laminar flame speed calculations. Cross reactions between benzylperoxy radicals and n-heptane improved the model prediction,,; of shock tube experiments for phi = 1.0 and temperatures lower than 800 K for an n-heptane/toluene fuel mixture, but cross reactions had no influence on HCCI Simulations.
|
|
| 3. |
- Angelin, Marcus, et al.
(författare)
-
Diastereoselective One-Pot Tandem Synthesis of 3-Substituted Isoindolinones : A Mechanistic Investigation
- 2010
-
Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 75:17, s. 5882-5887
-
Tidskriftsartikel (refereegranskat)abstract
- The mechanism of a base-catalyzed one-pot reaction of 2-cyanobenzaldehyde and primary nitroalkanes, to produce 3-substituted isoindolinones, has been investigated. A route starting with a nitroaldol (Henry) reaction, followed by a subsequent cyclization and rearrangement, was supported by intermediate analogue synthesis and DFT calculations. Direct diastereoselective crystallization from the reaction mixture was also achieved and studied for a number of substrates. Furthermore, the 3-substituted isoindolinones are an interesting group of compounds, both present important natural products, as well as being precursors to other valuable building blocks.
|
|
| 4. |
|
|
| 5. |
|
|
| 6. |
- Besharat, Zahra, et al.
(författare)
-
Dehydrogenation of methanol on Cu2O(100) and (111)
- 2017
-
Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 146:24
-
Tidskriftsartikel (refereegranskat)abstract
- Adsorption and desorption of methanol on the (111) and (100) surfaces of Cu2O have been studied using high-resolution photoelectron spectroscopy in the temperature range 120-620 K, in combination with density functional theory calculations and sum frequency generation spectroscopy. The bare (100) surface exhibits a (3,0; 1,1) reconstruction but restructures during the adsorption process into a Cu-dimer geometry stabilized by methoxy and hydrogen binding in Cu-bridge sites. During the restructuring process, oxygen atoms from the bulk that can host hydrogen appear on the surface. Heating transforms methoxy to formaldehyde, but further dehydrogenation is limited by the stability of the surface and the limited access to surface oxygen. The (root 3 x root 3)R30 degrees-reconstructed (111) surface is based on ordered surface oxygen and copper ions and vacancies, which offers a palette of adsorption and reaction sites. Already at 140 K, a mixed layer of methoxy, formaldehyde, and CHxOy is formed. Heating to room temperature leaves OCH and CHx. Thus both CH-bond breaking and CO-scission are active on this surface at low temperature. The higher ability to dehydrogenate methanol on (111) compared to (100) is explained by the multitude of adsorption sites and, in particular, the availability of surface oxygen.
|
|
| 7. |
- Bittererova, M., et al.
(författare)
-
A theoretical study of the azide (N-3) doublet states. A new route to tetraazatetrahedrane (N-4) : N+N-3 -> N-4
- 2002
-
Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 116:22, s. 9740-9748
-
Tidskriftsartikel (refereegranskat)abstract
- The potential energy surfaces for the low-lying doublet states of the azide radical (N-3) have been computed at the complete active space self-consistent field (CASSCF) level with the CAS(15,12) active space. The cc-pVTZ and aug-cc-pVTZ basis sets have been employed throughout the present work. Energies, geometries and harmonic frequencies were determined for the N-3 linear ground electronic state ((2)Pi(g)), a stable C-2v ring structure (B-2(1)), and a C-s transition state ((2)A(')) connecting the ring and linear structures. Other N-3 (C-2v) stationary points ((2)A(2), B-2(1), and (2)A(1)) have been characterized, as well. The vertical excitation energies for the doublet excited states of the N-3 linear ((2)Pi(g)) and stable ring (B-2(1)) isomers were calculated using CASSCF and multireference configuration interaction [MRCI-SD(Q)] methods. A new route to tetraazatetrahedrane [N-4(T-d)] has been proposed on the N-4 singlet potential energy surface within C-s symmetry. MRCI-SD(Q) calculations predict that N-4 (T-d) can be formed from atomic nitrogen in the D-2 state and N-3 (C-2v, B-2(1)) in a barrierless exothermic reaction. The energy difference (D-0) is 135.4 kcal/mol at the MRCI-SD(Q) level.
|
|
| 8. |
- Bittererova, M., et al.
(författare)
-
Ab initio study of the ground state and the first excited state of the rectangular (D-2h) N-4 molecule
- 2001
-
Ingår i: Chemical Physics Letters. - 0009-2614 .- 1873-4448. ; 347:03-jan, s. 220-228
-
Tidskriftsartikel (refereegranskat)abstract
- The dissociation pathway of D-2h N-4 has been investigated at the CASSCF level of theory. A new C-2v transition state to dissociation was found and characterized on the potential energy surface. The effective barrier of dissociation from D-2h N-4 to 2N(2) is estimated to 6.5 kcal/mol from MR-AQCCNTZ//CAS(12,12)/VTZ calculations. Vertical excitation energies and oscillator strengths for the lowest 20 singlet states of D-2h N-4 have been calculated using the EOM-CCSD method. The geometry of the first excited state B-1(3u), considered as the lowest optically accessible state, has been optimized and characterized at various computational levels. This state might be useful for detection of D-2h N-4 by means of laser-induced fluorescence (LIF) spectroscopy.
|
|
| 9. |
- Bittererova, M., et al.
(författare)
-
Theoretical study of the singlet electronically excited states of N-4
- 2001
-
Ingår i: Chemical Physics Letters. - 0009-2614 .- 1873-4448. ; 340:06-maj, s. 597-603
-
Tidskriftsartikel (refereegranskat)abstract
- Vertical excitation energies for the lowest eleven singlet states of T-d N-4 were calculated using the TD-DFT method with the B3LYP functional, and at the EOM-CCSD level of theory. The vertical excitation energies for the five lowest-lying excited states were also obtained using the state-averaged CASSCF, CASPT2, CASPT3, and MRCI + Q methods. Our results show that the five lowest-lying states are of valence character. EOM-CCSD/d-aug-cc-pVTZ calculations predict that there are two weakly allowed optical transitions of T-2 symmetry at 10.44 and 10.82 eV. The transition to the third T-2 state, which is predicted to be at 10.89 eV, has an oscillator strength about one order of magnitude higher.
|
|
| 10. |
- Bittererova, M., et al.
(författare)
-
Theoretical study of the triplet N-4 potential energy surface
- 2000
-
Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 104:51, s. 11999-12005
-
Tidskriftsartikel (refereegranskat)abstract
- The N-4 molecule in its triplet state has been studied using the DFT-B3LYP, CASSCF, and CCSD(T) computational methods. The previously reported C-s ((3)A ) minimum was not found to be stable using these methods. A D-2d ((3)A(1)) minimum was found to be the lowest energy triplet with a closed structure. This minimum is 20.2 kcal/mol higher in energy than T-d ((1)A(1)) N-4 at the CCSD(T)/cc-pVTZ//CCSD(T)/DZP level of theory. The barrier to dissociation has been estimated to ca. 7.5 kcal/mol from CAS(8,8)+MR-ACPF and CAS(8,8)+MR-AQCC calculations. CASSCF(12,12) calculations indicate that the open-chain N-4 Of C-2h (B-3(u)) symmetry is not stable. The open-chain C-s((3)A ) structure has been found to be a true minimum at all investigated levels of theory. It is 13.4 kcal/mol lower in energy than T-d ((1)A(1)) N-4 at the CCSD(T)/cc-pVTZ//CCSD(T)/DZP level.
|
|
