INNER-SHELL EXCITATION SPECTROSCOPY OF CLOSO-CARBORANES

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 bee n derived from inner-shell electron energy loss spectra (ISEELS) recor ded under electric dipole-scattering conditions. Total ion yield spect ra recorded at high resolution with synchrotron radiation are also rep orted. The spectral features are assigned on the basis of comparisons with spectral predictions derived from the results of ab initio and se miempirical (extended Huckel) molecular orbital calculations. The isom eric and core level variations in the discrete core excitations are re lated to changes in orbital symmetries as well as variations in electr on localization in these isomers. The ionization efficiency in the reg ion of the B 1s and C 1s edges is derived.