Inner-Shell Excitation Spectroscopy of closo-Carboranes

Abstract

Oscillator strength spectra in the region of B 1s and C 1s excitation of three isomeric carborane cage compounds [closo-1,2-orthocarborane, closo-1,7-metacarborane, closo-1,12-paracarborane (C2B10H12)] have been derived from inner-shell electron energy loss spectra (ISEELS) recorded under electric dipole-scattering conditions. Total ion yield spectra recorded at high resolution with synchrotron radiation are also reported. The spectral features are assigned on the basis of comparisons with spectral predictions derived from the results of ab initio and semiempirical (extended Hückel) molecular orbital calculations. The isomeric and core level variations in the discrete core excitations are related to changes in orbital symmetries as well as variations in electron localization in these isomers. The ionization efficiency in the region of the B 1s and C 1s edges is derived.

The electronic structure of 1,2-PCB10H11 molecular films: a precursor to a novel semiconductor

“…The arguments that 1,2-C 2 B 10 H 12 is more "p-type" due to the multiple bond character in the C-C bond [18] that we have used previously [17] would not seem to fully apply as an intra-icosahedral phosphorus adjacent to carbon should result in 1,2-PCB 10 H 11 exhibiting similar properties to 1,2-C 2 B 10 H 12 . It is true, however, that the electron affi nity level is some what lower for molecular 1,2-PCB 10 H 11 (the LUMO orbital energy is at −1.96 eV from the PM3 calculations) than for mo lecular 1,2-C 2 B 10 H 12 (the LUMO orbital energy is at −0.7 eV from the PM3 calculations) but this roughly 1 eV shift only partly accounts for the 3 to 4 eV shift observed between the 2 molecules, when adsorbed in multilayer fi lms on noble metal substrates.…”

“…Similar semi-empirical calculations [7,17,22,39] have been found to provide good agreement with photoemission and inverse photoemission ex periments, in spite of the simplistic methodology and the fact that these are ground state calculations [18]. These semi-empirical calculations of occupied and unoccupied molecu lar orbitals were undertaken following geometry optimiza tion and the calculation of the lowest restricted Hartree-Fock (RHF) energy states.…”

“…This difference in the placement of the chemical potential (Fermi level, E F ) is diffi cult to un derstand, as both molecules have identical electron counts and symmetry. The differences are also observed in the gas phase and thus may be an integral feature of orthocarborane and metacarborane molecules [17,18]. A possible explanation for the difference in the placement of the chemical potential may be in part due to the presence of the carbon-carbon bond and the possibility of multiple bond character between the two car bon atoms [17,18].…”

“…The differences are also observed in the gas phase and thus may be an integral feature of orthocarborane and metacarborane molecules [17,18]. A possible explanation for the difference in the placement of the chemical potential may be in part due to the presence of the carbon-carbon bond and the possibility of multiple bond character between the two car bon atoms [17,18]. Accordingly, the study described on an isoelectronic analogue to 1,2-C 2 B 10 H 12 , viz 1,2-PCB 10 H 11 , which lacks a C-C bond will provide some insight into this matter.…”

Electronic structure and polymerization of a self-assembled monolayer with multiple arene rings

“…[57][58][59][60] DFT generally results in a HOMO-LUMO gap too small by as much as a factor of 2 or more. Consideration of the possible multiconfigurational final states [60][61][62] is likely to provide a more accurate representation of the spectra, but orbital symmetry information is generally lost. A proper calculation of electronic structure should include the substrate ͑to properly account for charge transfer, thiolate formation, and charge screening͒, exchange and correlation energies, 63 but such slab calculations, 37,57,64 given the very large number of atoms per unit cell ͑39 atoms from one thiolate adsorbate alone͒, are computationally very expensive, even if at all possible.…”