Valence-bond studies of 4-electron 3-centre bonding units. I. The π-electrons of O3, NO2−, and CH2N2

Harcourt, Richard D.; Roso, Walter

doi:10.1139/v78-186

Cited by 76 publications

(29 citation statements)

References 16 publications

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“…Using Roso's ab initio valence bond ͑VB͒ program, 9 we have calculated values of EET matrix elements ͑eV͒ for the three types of systems that we are considering here, with 4 Å ͑as in Ref. 2͒ separation between CvC or CvO chromophores, and bond lengths of 1.34 Å for CvC and either 1.34 or 1.21 Å for CvO.…”

Section: Methods Of Calculationmentioning

confidence: 99%

On the origin of matrix elements for electronic excitation (energy) transfer

Harcourt

Ghiggino

Scholes

et al. 1996

The Journal of Chemical Physics

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Configuration interaction and the theory of electronic factors in energy transfer and molecular exciton interactionsStructure of complex systems using electronic excitation transport: Theory, Monte Carlo simulations, and experiments on micelle solutions Electronic excitation transfer in clustered chromophore systems: Calculation of timeresolved observables for intercluster transferThe origin of electronic energy transfer ͑EET͒ between two chromophores ͑D and A͒ is explored further for several molecular situations that may be encountered in experiment-namely, nonoverlapping active-space orbitals of the D and A chromophores, forbidden electronic excitations for both chromophores, and an allowed and a forbidden electronic excitation for the D and A chromophores, respectively. The theory is illustrated via the results of calculations of the EET matrix elements for model systems with both four-eight active-space electrons and all of the electrons included explicitly. In each case, it is found that any overlap contribution to these matrix elements is associated much more with charge-transfer and penetration terms rather than it is with the Dexter exchange integral. The calculated magnitude of the latter integral is always smaller than that of the Coulomb integral.

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Section: Methods Of Calculationmentioning

confidence: 99%

On the origin of matrix elements for electronic excitation (energy) transfer

Harcourt

Ghiggino

Scholes

et al. 1996

The Journal of Chemical Physics

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“…Each of the canonical structures 1 and 2 involves the spin pairing of electrons that singly occupy (weakly) overlapping sulfur or nitrogen pπ AOs, and therefore "long" or formal or secondary S-S or N-N bonds (with negligible strengths) will be formed in these structures. In ref 16, further comments with regard to the interpretation of the results of SC-VB calculations are provided.…”

Section: Some Comments On Valence Bond Structuresmentioning

confidence: 99%

On the Singlet Diradical Character of S₂N₂

et al. 1998

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The results of some 6-31G(d) CISD MO calculations for the ground state of cyclic S 2 N 2 are reported. They give sulfur 3pπ and nitrogen 2pπ NAO occupancies of 1.501 and 1.443, respectively. These results are interpreted to indicate that the nitrogen singlet diradical character is larger than the sulfur singlet diradical character. The results of STO-6G valence bond calculations of the energies of the sulfur and nitrogen singlet diradical structures are in accord with this conclusion. However STO-6G CISD calculations give sulfur 3pπ and nitrogen 2pπ NAO occupancies of 1.664 and 1.335, respectively, thereby implying that the STO-6G calculations overestimate the extent of nitrogen diradical character. Consideration is given to the use of two equivalent increased-valence structures to provide a valence bond representation of the electronic structure of S 2 N 2 . Regardless of the degree of nitrogen or sulfur singlet diradical character, resonance between these structures, which is equivalent to resonance between the two singlet diradical and four zwitterionic Lewis structures, must provide a lower energy VB represention than does that which is obtained by use of either singlet diradical structure alone.

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“…The Roso ab initio VB program, [7][8][9]11,12] together with the calculated geometry reported in ref. [3], and initially, best-atom atomic orbital (AO) exponents, [13] have been used to calculate the Chirgwin-Coulson [14] structural weights for these structures.…”

Section: Methods Of Calculationmentioning

confidence: 99%

“…(Atomic formal charges in VB structures are assigned on the assumption that bonding electrons are shared equally by pairs of adjacent atoms. [7][8][9][10][11][12][19][20][21] ) By delocalizing a fluorine 2pπ x electron of structure (1) into the bonding MO π x (NF) = 2pπ x (F) + l2pπ x (N), increasedvalence structure (14) is obtained. Similarly delocalization of a 2pπ y electron of structure (1) into the bonding MO π y (NF) = 2pπ y (F) + l2pπ y (N) generates the equivalent increased-valence structure (15), Scheme 1.…”

Section: Increased-valence Structures For N 2 F + and N 2 Omentioning

confidence: 99%

Valence Bond Studies of N2F+

Harcourt¹

2003

Aust. J. Chem.

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The results of STO-6G valence bond (VB) calculations for the linear cation N 2 F + show that (a) the dominant Lewis-type VB structures involve a single positive charge which is located on either of the nitrogen atoms, and (b) a small amount of N-F π-bonding arises primarily from the formation of one-electron N-F π-bonds. It is suggested that N-F π-bonding is one of several factors which are responsible for the shortening of the N-F bond of N 2 F + relative to that of NF + 4 . Valence bond and bond length considerations imply that the extent of N-O π-bonding in N 2 O and NO 3− 4 exceeds the degree of N-F π-bonding in N 2 F + and NF + 4 .

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Valence-bond studies of 4-electron 3-centre bonding units. I. The π-electrons of O₃, NO₂⁻, and CH₂N₂

Cited by 76 publications

References 16 publications

On the origin of matrix elements for electronic excitation (energy) transfer

On the origin of matrix elements for electronic excitation (energy) transfer

On the Singlet Diradical Character of S₂N₂

Valence Bond Studies of N2F+

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Valence-bond studies of 4-electron 3-centre bonding units. I. The π-electrons of O3, NO2−, and CH2N2

Cited by 76 publications

References 16 publications

On the origin of matrix elements for electronic excitation (energy) transfer

On the origin of matrix elements for electronic excitation (energy) transfer

On the Singlet Diradical Character of S2N2

Valence Bond Studies of N2F+

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Valence-bond studies of 4-electron 3-centre bonding units. I. The π-electrons of O₃, NO₂⁻, and CH₂N₂

On the Singlet Diradical Character of S₂N₂