PNNL

Abstract

We report nonresonant inelastic x-ray scattering (NRIXS) measurement of core-shell excitations from both B 1s and C 1s initial states in all three isomers of the dicarba-closo-dodecaboranes C2B10H12. First, this data yields an experimental determination of the angular-momentum-projected final local density of states (l-DOS). We find low-energy resonances with distinctive local s- or p-type character, providing a more complete experimental characterization of bond hybridization than is available from dipole-transition limited techniques, such as x-ray absorption spectroscopies. This analysis is supported by independent density functional theory and real-space full multiple scattering calculation of the l-DOS which yield a clear distinction between tangential and radial contributions. Second, we investigate the isomer-sensitivity of the NRIXS signal, and compare and contrast these results with prior electron energy loss spectroscopy measurements. This work establishes NRIXS as a valuable tool for borane chemistry, not only for the unique spectroscopic capabilities of the technique, but also through its compatibility with future studies in solution or in high pressure environments. In addition, this work also establishes the real-space full multiple scattering approach as a useful alternative to traditional approaches for the excited states calculations for aromatic polyhedral boranes and related systems. This research was supported by DOE, Basic Energy Science, Office of Science, Contract Nos. DE-FGE03-97ER45628 and W-31-109-ENG-38, ONR Grant No. N00014-05-1-0843, Grant DE-FG03-97ER5623, NIH NCRR BTP Grant RR-01209, the Leonard X. Bosack and Bette M. Kruger Foundation, the Hydrogen Fuel Cell Initiative of DOE Office of Basic Energy Sciences, and the Summer Research Institute Program at the Pacific Northwest National Lab. Battelle operates the Pacific Northwest National Lab for DOE. The operation of Sector 20 PNC-CAT/XOR is supported by DOE Basic Energy Science, Office of Science, Contract No. DE-FG03-97ER45629, the University of Washington, and grants from the Natural Sciences and Engineering Research Council of Canada. Use of the Advanced Photon Source was supported by the U.S. Department of Energy, Basic Energy Sciences, Office of Science, under Contract W-31-109-Eng-38. We thank Mark Lee and Fred Hawthorne for providing some of the samples used in this study. We thank John Rehr, Aleksi Soininen, Adam Hitchcock, and Ed Stern for stimulating discussions.