On the role of 3d orbitals in sulfur

Strömberg, Ann; Wahlgren, Ulf; Pettersson, Lars G. M.; Siegbahn, Per E. M.

doi:10.1016/0301-0104(84)85059-4

Cited by 34 publications

(9 citation statements)

References 9 publications

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“…included. However, such effects on CS bonds do not appear to markedly longer than in the singlet-thiohydroxymethylenes and be as large as those found in the case of the SO bonds (40).…”

Section: Structuresmentioning

confidence: 65%

Features of the thioformaldehyde potential energy surfaces

Goddard¹

1985

Can. J. Chem.

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The structures of seven minima and five transition states of the S0 and T1 potential energy surfaces of thioformaldehyde have been located at the 3-21G* SCF level. Further calculations have been carried out to determine harmonic vibrational frequencies and to examine the effects of larger basis sets and of configuration interaction on energy differences. The molecular dissociation limit of H2 and CS is thermodynamically accessible at the energy of the lowest n,π* excited states and the singlet thiohydroxymethylenes lie only slightly too high. However, there are large barriers of ~85 to 90 kcal mol−1 to the molecular dissociation or to the 1,2-hydrogen shifts from thioformaldehyde to the thiohydroxymethylenes. The dissociation to H and HCS requires ~85.4 kcal mol−1 on the ground singlet and faces a barrier of several kcal mol−1 relative to products on the triplet surface. Any unimolecular photochemistry of thioformaldehyde is likely to require excitation to higher excited states than the lowest n,π* states.

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“…included. However, such effects on CS bonds do not appear to markedly longer than in the singlet-thiohydroxymethylenes and be as large as those found in the case of the SO bonds (40).…”

Section: Structuresmentioning

confidence: 65%

Features of the thioformaldehyde potential energy surfaces

Goddard¹

1985

Can. J. Chem.

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“…Our first guess was that the additional d function (exponent 0.014204) enhances the representation of the 3d orbital of sulfur. The latter is known to participate actively in the bonding of hypervalent sulfur 33 and might be important in the excited states, too. However, additional test calculations showed that the considerable red shift is brought about mainly by the diffuse p function (exponent 0.009988).…”

Section: Ground State Geometry and Vertical Transition Energiesmentioning

confidence: 99%

Excited states of thiophene: ring opening as deactivation mechanism

Salzmann

Kleinschmidt

Tatchen

et al. 2008

Phys. Chem. Chem. Phys.

121

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(Time-dependent) Kohn-Sham density functional theory and a combined density functional/multi-reference configuration interaction method (DFT/MRCI) were employed to explore the ground and low-lying electronically excited states of thiophene. Spin-orbit coupling was taken into account using an efficient, nonempirical mean-field Hamiltonian. Phosphorescence lifetimes were calculated by means of spock.ci, a selecting direct multi-reference spin-orbit configuration interaction program. Throughout this paper, we use the following nomenclature: S1, S2,..., T1, T2,..., denominate electronic structures in their energetic order at the ground state minimum geometry, whereas S1, S2,..., T1, T2,..., refers to the actual order of electronic states at a given nuclear geometry. Multiple minima were found on the first excited singlet (S1) potential energy hypersurface with electronic structures S1 (piHOMO-1-->pi+piHOMO-->pi), S2 (piHOMO-->pi), and S3 (piHOMO-->sigma*) corresponding to the 2 1A1 (S1), 1 1B2 (S2), and 1 1B1 (S3) states in the vertical absorption spectrum, respectively. The S1 and S2 minimum geometries show out-of-plane deformations of the ring. The S3 electronic structure yields the global minimum on the S1 surface with an adiabatic excitation energy of merely 3.81 eV. It exhibits an asymmetric planar nuclear arrangement with one significantly elongated C-S bond. A constrained minimum energy path calculation connecting the S1 and S3 minima suggests that even low-lying vibrational levels of the S1 potential well can access the global minimum of the S1 surface. Nonradiative decay of the electronically excited singlet population to the electronic ground state via a close-by conical intersection will be fast. According to our work, this ring opening mechanism is most likely responsible for the lack of fluorescence in thiophene and the ultrafast decay of the S1 vibrational levels, as observed in time-resolved pump-probe femtosecond multiphoton ionization experiments. An alternative relaxation pathway leads from the S1 minimum via vibronic coupling to the S2 potential well followed by fast inter-system crossing to the T2 state. For an estimate of individual rate constants a quantum dynamical treatment will be required. The global minimum of the T1 surface has a chair-like nuclear conformation and corresponds to the T1 (1 3B2, piHOMO-->pi) electronic structure. Phosphorescence is weak here with a calculated radiative lifetime of 0.59 s. For the second potential well on the T1 surface with T3 (1 3B1, piHOMO-->sigma*) electronic structure, nonradiative processes are predicted to dominate the triplet decay.

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“…The importance of achieving a proper polarization of the central atom was investigated by using two different polarized split-valence bases, which include two sets of d functions on S. These bases were constructed from the standard 6-3 lG* one, by replacing the standard set of d functions on sulfur by two sets of exponents, 0.39 and 1.18 in one case (22), and 0.30 and 0.80 in the other (14). Energies obtained with the first set of exponents were systematically lower than those obtained with the second; we shall therefore discuss exclusively the results obtained with the former basis, which will be denoted as 6-31G*+d,.…”

Section: Computational Detailsmentioning

confidence: 99%

“…Regarding the concrete aspects of the SCF ab initio treatment of sulfamide, it is worth noticing that the choice of the basis set, which constitutes one of the most crucial problems of any ab initio calculation, becomes particularly relevant in the present case, where the second-row atom displays a hypervalent coordination (7,(9)(10)(11)(12)(13)(14)(15)(16)(17). Moreover, the high electronegativity of the ligands bonded to sulfur in this system will likely render polarization effects quite important, so that a proper description of the polarization of the first-row atoms would also be unavoidable.…”

Section: Introductionmentioning

confidence: 99%

A molecular orbital study of the conformation (inversion and rotational barriers) and electronic properties of sulfamide

Mó¹,

Paz²,

Yáñez³

et al. 1989

Can. J. Chem.

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Chem. 67, 2227 (1989).Ab initio calculations have been used to study the conformational potential surface of sulfamide, by considering the S-N bond rotations and the nitrogen inversion processes. The lowest energy conformation (b) is found for a cis-trans arrangement of the amino groups, although conformations with cis-cis (a), trans-trans (c), and near staggered (c') arrangements lie close in energy. Nitrogen inversion barriers are very low, and consequently one may expect forms b and c' to be the only ones present in the gas phase. Conformer a is very polar, its dipole moment being twice that of b, so it may be favored in condensed media or in polar-solvent solutions. The relative stability of the different isomers is governed by interactions between the amino protons and between the nitrogen lone pairs. Our results show that d-n backbonding, involving the d orbitals on sulfur, is responsible for the multiple bond character of the S-0 linkage, but is very small in the S-N interactions. The role of the sulfur d-orbital exponent, when a 6-31G* basis is used, is analyzed on a series of model compounds containing S", STV, and SV1. Although the inclusion of d functions on sulfur is crucial to describing correctly the bonding in sulfamide, the results obtained do not change appreciably if a second set of d functions is centered on sulfur. Nevertheless, only when polarization functions are also included for first-row atoms is the description of the system reliable.Key

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On the role of 3d orbitals in sulfur

Cited by 34 publications

References 9 publications

Features of the thioformaldehyde potential energy surfaces

Features of the thioformaldehyde potential energy surfaces

Excited states of thiophene: ring opening as deactivation mechanism

A molecular orbital study of the conformation (inversion and rotational barriers) and electronic properties of sulfamide

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