Temporary anion states of closo-carboranes and diethyl carborane

The energies required to attach electrons into the low-lying normally unoccupied molecular orbitals of the carborane (C2B10H12) cage compounds closo-1,2-, closo-1,7-, and closo-1,12-dicarbadodecacarborane, and those of diethyl carborane (nido-dicarbahexacarborane) are determined by electron transmission spectroscopy in the gas phase. The lowest lying anion state in each of these compounds in the equilibrium geometry of the neutral molecule is found to be unstable with respect to electron ejection, and is formed at a vertical attachment energy of approximately 1 eV. The total yield of negative ions produced by electron impact on ortho-carborane was measured and observed to peak near 0 eV and at 0.7 eV. The latter feature has a cross section of 5.1 x 10(-17) cm(2). Our data are consistent in energy dependence with relative yield measurements made elsewhere in which the charged product was identified as a metastable anion state of the parent molecule. The results from our calculations seeking to identify the geometry of this anion are reported.