| 1. |
- Bittererova, M., et al.
(författare)
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A theoretical study of the azide (N-3) doublet states. A new route to tetraazatetrahedrane (N-4) : N+N-3 -> N-4
- 2002
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 116:22, s. 9740-9748
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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.
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| 2. |
- Bittererova, M., et al.
(författare)
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Ab initio study of the ground state and the first excited state of the rectangular (D-2h) N-4 molecule
- 2001
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Ingår i: Chemical Physics Letters. - 0009-2614 .- 1873-4448. ; 347:03-jan, s. 220-228
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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.
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| 3. |
- Bittererova, M., et al.
(författare)
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Theoretical study of the singlet electronically excited states of N-4
- 2001
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Ingår i: Chemical Physics Letters. - 0009-2614 .- 1873-4448. ; 340:06-maj, s. 597-603
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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.
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| 4. |
- Bittererova, M., et al.
(författare)
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Theoretical study of the triplet N-4 potential energy surface
- 2000
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 104:51, s. 11999-12005
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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.
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| 5. |
- Carlqvist, Peter, et al.
(författare)
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Computational study of the amination of halobenzenes and phenylpentazole. A viable route to isolate the pentazolate anion?
- 2004
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Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 69:9, s. 3222-3225
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Tidskriftsartikel (refereegranskat)abstract
- Amination of halobenzenes, which proceeds via the benzyne intermediate (1), has been studied using quantum chemical methods. The computational data are in agreement with experimentally observed trends in reactivity and provide a qualitative explanation for the observed hydrogen isotope effects. To investigate if this is a viable way to isolate the pentazolate anion (2), the reactivities of the halobenzenes have been compared to phenylpentazole (3). The reaction energetics for phenylpentazole become favorable after complexation with Zn2+.
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| 6. |
- Carlqvist, Peter, et al.
(författare)
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The stability of arylpentazoles
- 2004
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 108:36, s. 7463-7467
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Tidskriftsartikel (refereegranskat)abstract
- The stability of phenylpentazole along with para-substituted and ortho,para-substituted arylpentazoles have been studied using high-level density functional theory (DFT). The decomposition of arylpentazoles to N-2 and the corresponding azide is a first-order reaction, where the breaking of the N1-N2 bond is concomitant with cleavage of the N3-N4 bond. Calculations confirm that the stability of arylpentazoles increases with electron-donating groups and decreases with electron-withdrawing groups, in the para position, as found in experiments. The stabilizing effect of the electron-donating groups is shown to be due to a resonance interaction with the electron-withdrawing pentazole ring. Addition of solvation effects, using the polarizable continuum model to simulate the polar solvent methanol, increases the stability of arylpentazoles. This is due to a more polar ground state than transition state. The calculated free energies of activation for the arylpentazoles agree well with experimental results. From the calculations, the electron-withdrawing effect of the pentazole group is found to be similar to that of cyanide (-CN). Some new arylpentazoles with hydroxyl groups in the ortho position are proposed. These are predicted to be more stable than all previously synthesized neutral arylpentazoles.
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| 7. |
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| 8. |
- Svanqvist, M., et al.
(författare)
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Single-shot stand-off detection of explosives precursors using UV coded aperture Raman spectroscopy
- 2015
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Ingår i: Chemichal, Biological, Radiological, Nuclear, and Explosives (CBRNE) Sensing XVI. - : SPIE. - 9781628415711
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Konferensbidrag (refereegranskat)abstract
- We present preliminary results on the performance of a basic stand-off Raman spectroscopy setup using coded apertures compared to a setup using a round-to-slit fiber for light collection. Measurements were performed using single 5 ns laser shots at 355 nm with a target distance of 5.4 meters on ammonium nitrate powder. The results show an increase in signal-to-noise ratio of 3-8 times when using coded aperture multiplexing compared to the fiber setup.
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