Experimental and theoretical comparison of the electronic structures of ethylene and diborane

Abstract

1.14 eV) than was found (with more limited basis sets) for 7 ionization of benzene9 (0.4 eV) or pyridine10 (0.6 eV). We therefore expect that tt excitation to low-lying states in these (and other) larger -electron systems will cause rearrangement of relatively less importance than the already small amount found in ethylene. This will then mean that one can indeed use the fixed core, -electron approximation as a quantitatively accurate quantum chemical method for such problems (this is implicit in previous work1112). It would be most interesting to see accurate ab initio calculations for larger tt systems (e.g., naphthalene)using the procedures we used for ethylene: it may be that for such large systems even tt excitation to Rydberg states or tt ionization would be moderately well represented with the fixed -core restriction.Acknowledgment. . E. S. acknowledges partial support of this work through a grant from the Petroleum Research Fund, administered by the American Chemical Society. We are also grateful to University Computing Company for a grant from the Chemical Applications Department, which enabled us to perform these calculations. Thanks are due Dr. R. Gilman for a preprint of his paper.12

Molecular Orbital Analysis of the Trend in 11B NMR Chemical Shifts for (Cp*M)2B5H9 (M = Cr, Mo, W; Cp* = η5-C5Me5)

“…This aspect of the MO structure is consistent with earlier studies of the effects of bridging hydrogens on electronic structure and is corroborated by the substantial 11 B downfield shift associated with the removal of a B−H−M bridge proton by a base . The classic example is the PES study of isoelectronic diborane and ethylene, in which ionization potential associated with the B−H−B MO's of B 2 H 6 is found to be several electronvolts higher than that of the π ionization of C 2 H 4 1 Pertinent MO Parameters for (Cp*M) 2 B 5 H 9 (M = Cr, Mo, W) AO coefficientsMO E (eV)character% MB 1,5 B 2,4 B 3 type 45 Cr −6.3 MB ab a 58 0.36 0.18 0.39 2p x Mo −4.8 MM b a 56 0.38 0.28 0.41 +2p y b,c W −4.7 50 0.30 0.25 0.45 44 Cr −8.0 MB ab 60 0.39 0.42 0.15 2p x Mo −6.2 MM b 52 0.39 0.41 0.08 +2p y b,c W −6.1 50 0.38 0.31 0.14 41 Cr −13.4 MB b 49 0.13 0.38 0.03 2p z b,d Mo −13.2 MM ab 39 0.15 0.43 0.00 W −13.2 33 0.10 0.38 0.01 40 Cr −13.9 MB b 31 0.07 0.30 0.44 2p z b,d Mo −14.0 MM b 24 0.07 0.29 0.49 W e −14.4 17 0.05 0.30 0.46 a ...…”

Assessment of Density-Functional Tight-Binding Ionization Potentials and Electron Affinities of Molecules of Interest for Organic Solar Cells Against First-Principles GW Calculations

“…The Hartree-Fock (HF) KT IPs are better from the point of view of Coulson Group I, but tend to slightly overestimate the experimental IPs. This is consistent with early literature, which proposed as a rule of thumb that agreement between HF KT and photoelectron spectroscopy (PES) IPs could be improved by multiplying the HF KT values by a factor of less than one (e.g., 0.92 or the "8% rule" [87,88]). Surprisingly, localizing the HF exchange operator by the optimized effective, potential method (OEP) so as to obtain an exact exchange-only xc-potential which includes a derivative discontinuity, leads to much improved absolute agreement between KT and experimental IPs with a slightly reduced standard error (∆y).…”

Temporary anion states of polyatomic hydrocarbons

“…The v2 spacing is 201 meV in the neutral molecule36 and 153 meV in the ground state of the cation. 37 The v3 spacing in the neutral molecule is 153 meV. 36 The energy loss experiments of Walker et al 32 show that upon decay the resonance, formed at 1.8-eV incident electron energy, excites v2 most strongly, with intermediate excitation of v3 and weak excitation of v4 (374 meV in the neutral molecule).…”