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- 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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