ELECTRONIC AND PHOTOELECTRON SPECTRA OF SOME CARBORANES
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Date
1974
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Ohio State University
Abstract
The electronic absorption spectra in the range from 40 000 to 77 000 $cm^{-1}$ and the photoelectron spectra (PES) up to 20 eV have been recorded for the carboranes $1,5 - C_{2}B_{3}H_{5}, 1,6 - C_{2}B_{4}H_{6}, 2,4 - C_{2}B_{5}H_{7}$ and $4,5 - C_{2}B_{4}H_{8}$. In 1,6 - $C_{2}B_{4}H_{6}$, three Rydberg series having quantum defects of 0.54, 0.09 and 0.03 can be discerned. These all lead to the first ionization potential of 78 720 $\pm$20 $cm^{-1}$. The PES yields the same value for the first ionization potential. The optical spectrum of $4,5 - C_{2}B_{4}H_{8}$ is diffuse except for one structured transition. This has been shown to be a Rydberg transition by the effect of a high pressure blanket of nitrogen upon it. Its term value with respect to the $0 - 0$ band of the PES ($IP = 75 800 cm^{-1}$) leads to a quantum defect of 0.51, Suggesting assignment as a p-Rydberg. In $1,5 - C_{2}B_{3}H_{5}$, two possible Rydberg series leading to the first ionization potential of 73 880 $cm^{-1}$ can be located. The PES assignments will be discussed with the aid of an all electron Gaussian orbital ab initio calculation and comparison to the alkane analog bicyclo-[1.1.1]-pentane will be made. The optical spectrum of $2,4 - C_{2}B_{5}H_{7}$ is completely diffuse and no assignments are possible. The PES yields a first ionization potential of 10.66 $\pm$ 0.03 eV (86 000 $cm^{-1}$), the highest by 0.9 eV of the carboranes studied.
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$^{1}$J. W. Raymonda gratefully acknowledges the hospitality of Bell Laboratories during the summer of 1971 when much of data reported here was obtained.
Author Institution: Calspan Corporation; Bell Laboratories Murray
Author Institution: Calspan Corporation; Bell Laboratories Murray