THEORETICAL ASSIGNMENT OF THE UV SPECTRA OF ALKYL RADICALS
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Publisher:Ohio State University
ABSTRACT Ab initio SCF and CI calculations have been performed to assign the UV spectra of the ethyl, isopropyl and t-butyl radicals. Contrary to previous speculation, the low lying states are shown to be predominantly Rydberg in character. The most noteworthy feature of the UV spectra of these series of alkyl radicals, including also the methyl radical, is the red-shift obtained with increasing number of methyl groups adjacent to the radical carbon. This red-shift is explained by the increased stability of the carbonium ion core of the Rydberg states as the number of methyl groups increases. A more detailed investigation has been undertaken for the ethyl radical, for which the 3p spectrum shows a broad main peak with two small extra peaks on the long wavelength side. To interprete this part of the spectrum the stability of the 3p states toward dissociation is assessed. The small peaks are probably transitions to two bound 3p states of a non-classical structure of the ethyl radical with one hydrogen bridging the two carbons. The Rydberg states of this geometry are shown to be of lower energy than the vertical structure by an amount that corresponds to the distance between the main peak and the small peaks. The main broad peak can be understood if one of the 3p states can be shown to be dissociative and possible dissociation paths are investigated.
Author Institution: IBM Research Laboratory; BRL, Aberdeen Proving Ground; Institute of Theoretical Physics, University of Stockholm
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