Studies of molecular ions. IX. Detection of low‐lying ‘non‐<i>Koopmans</i>’ states in polyacetylene molecular cations

Haselbach, Edwin; Klemm, Urs; Buser, Urs; Gschwind, Rudolf; Jungen, Martin; Kloster‐Jensen, Else; Maier, John P.; Marthaler, Oskar; Christen, Heniz; Baertschi, P.

doi:10.1002/hlca.19810640321

Cited by 18 publications

(4 citation statements)

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“…A comparison between the PE spectra of dimethyl- and disilylacetylene reveals a higher (10.46 eV) ionization energy for the silyl substituted compound than for dimethylacetylene (9.61 eV) as expected for the less electron donor properties of the SiH 3 group compared with the CH 3 group. The photoelectron spectra of bis(trimethylsilyl)di- and triacetylene show a shift of the π-bands toward lower energy when compared to the t -butyl substituted congeners . The results when acetylene and 1,3-butadiyne were substituted with (H 3 C) 3 Ge , and (H 3 C) 3 Sn were similar.…”

Section: Quantum Chemical Calculations and Spectroscopic Investigatio...mentioning

confidence: 87%

Alkynes Between Main Group Elements: From Dumbbells via Rods to Squares and Tubes

Gleiter

Werz

2010

Chem. Rev.

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Introduction 4447 2. Alkynes Substituted by Elements of Main Groups I-IV (Except Carbon) 4449 2.1. Alkynes Substituted by Elements of Main Groups I and II 4449 2.1.1. Alkali and Alkali Earth Metal Derivatives of Alkynes 4449 2.1.2. Alkali and Alkali Earth Metal Carbides 4450 2.1.3. Quantum Chemical Calculations on the Metal-Alkyne Interaction of Group II Metals 4451 2.2. Alkynes Substituted by Elements of Main Group III 4451 2.

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Section: Quantum Chemical Calculations and Spectroscopic Investigatio...mentioning

confidence: 87%

Alkynes Between Main Group Elements: From Dumbbells via Rods to Squares and Tubes

Gleiter

Werz

2010

Chem. Rev.

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“…However, optical transitions involving electron promotion to virtual orbitals, (B-and C-type transitions in Scheme 1), which bear no direct relation to Koopmans' theorem, are also observed in radical ion spectra. [11][12][13] On the basis of the above concepts, we concluded some time ago that the energies E i of A-type transitions in a radical cation (where the nth MO is singly occupied) should correspond to differences of orbital energies ∆ i ) n -(n-i) calculated for the corresponding neutral, closed-shell compound containing 2n electrons. Furthermore, we demonstrated that optical transition energies of radical cations can be successfully predicted using this approach based on Koopmans' theorem, even for systems that undergo large geometry changes upon ionization, by carrying out the calculations at the optimized geometries of the radical cations (we termed these "neutral at cation geometry" or NCG calculations).…”

Section: Introductionmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

“…Haselbach, Shida, and co-workers pointed out the relationship of these observations to Koopmans' theorem, which states that ionization potentials of neutral, closed shell molecules are equal to the negative of their orbital energies, −ε i . However, optical transitions involving electron promotion to virtual orbitals, (B- and C-type transitions in Scheme ), which bear no direct relation to Koopmans' theorem, are also observed in radical ion spectra. −

1 Generic MO Scheme for a Radical Cation (Left Side) and a Radical Anion (Right Side) …”

Section: Introductionmentioning

confidence: 99%

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Calculations of the Optical Spectra of Hydrocarbon Radical Cations Based on Koopmans' Theorem

et al. 2007

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The first few bands in the optical spectra of radical cations can often be interpreted in terms of A-type transitions that involve electron promotions from doubly occupied to the singly occupied molecular orbital (SOMO) and/or B-type transition which involve electron promotion from the SOMO to virtual molecular orbitals. We had previously demonstrated that, by making use of Koopmans' theorem, the energies of A-type transitions can be related to orbital energy differences between lower occupied MOs and the highest occupied MO (HOMO) in the neutral molecule, calculated at the geometry of the radical cation. We now propose that the energies of B-type transitions can be related similarly to energy differences between the lowest unoccupied MO (LUMO) and higher virtual MOs in the dication, also calculated at the geometry of the radical cation, by way of an extension of Koopmans' theorem to virtual MOs similar to that used sometimes to model resonances in electron scattering experiments. The optical spectra of the radical cations of several polyenes and aromatic compounds, the matrix spectra of which are known (or presented here for the first time), and for which CASSCF/CASPT2 calculations are available, are discussed in terms of these Koopmans-based models. Then the spectra of five poly(bicycloalkyl)-protected systems and that of hexabenzocoronene, compounds not amenable to higher level calculations, are examined and it is found that the Koopmans-type calculations allow a satisfactory interpretation of most of the features in these spectra. These simple calculations therefore provide a computationally inexpensive yet effective way to assign optical transitions in radical ions. Limitations of the model are discussed.

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Darstellung, Reaktionen und Struktur von tert‐Butyl(tert‐butylimino)boran

et al. 1984

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Preparation, Reactions, and Structure of tert-Butyl(tert-buty1imino)boraneThe iminoborane t BuB = Nt Bu (1) is formed from the aminoborane Cl(t Bu)B-N(t Bu)SiMe, by the elimination of Me,SiCI in the gas phase at 530°C. Compound 1 slowly dimerizes to the diazadiboretidine [tBuBNtBu], (2). In a way typical for iminoboranes, the borane 1 undergoes a? ethyloboration with BEt,, a [2 + 31-cycloaddition with PhN,, and an azidosilation with Me3SiN3. The crystal and molecular structure of 1 and 2 are described; there is a linear central CBNC-chain in 1 with a BN-bond distance of 125.8 pm; the ring-skeleton of 2 deviates from planarity by the influence of the bulky ring ligands. The structural properties of the iminoborane 1 are comparable to those of the isoelectronic alkyne fBuC=CtBu (3). and the properties of the cyclodimer 2 are comparable to those of the isoelectronic cyclobutadiene [t BuC = Ct Bu], (4). The strength of the triple bond decreases from 3 to 1 in a similar manner as by going from N, to CO. Darstellung und Reaktionen von tert-Butyl(tert-buty1imino)boran (1)Aus dem Aminoboran Cl(tBu)B -N(tBu)SiMe,, das aus dem Chlorboran C1,BtBu und dem Lithiumamid LiN(tBu)SiMe, zuganglich ist, laBt sich in der bekannten 0

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Studies of molecular ions. IX. Detection of low‐lying ‘non‐Koopmans’ states in polyacetylene molecular cations

Abstract: Comparison of the photoelectron spectra of the title compounds with the electronic absorption spectra of the corresponding radical cations led to the detection of low lying ‘Non‐Koopmans’‐states in the ionic species.

Cited by 18 publications

References 8 publications

Alkynes Between Main Group Elements: From Dumbbells via Rods to Squares and Tubes

Alkynes Between Main Group Elements: From Dumbbells via Rods to Squares and Tubes

Calculations of the Optical Spectra of Hydrocarbon Radical Cations Based on Koopmans' Theorem

Darstellung, Reaktionen und Struktur von tert‐Butyl(tert‐butylimino)boran

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