SOME DIATOMIC AND TRIATOMIC FREE RADICALS TRAPPED AT $4.2^{\circ} K$
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Date
1958
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Ohio State University
Abstract
“The radicals $NH_{2}$, $HNO_{3}$, $NO_{2}, NH, OH, C_{3}$ and CH have been trapped at $4.2^{\circ} K$ from the products of an electrical discharge sustained in argon as matrix material mixed with a small amount of the appropriate parent molecule. These species can be conclusively identified by their well known electronic absorption spectra. Because of environmental perturbations of the electronic states and to a lesser extent the vibrational levels, red and blue “matrix shifts” of upward to $300 cm^{-1}$ occur. The absorption “bands” of $NH_{2}$ are exceedingly sharp ($<3 cm^{-1}$ wide), and transitions from a metastable rotational level indicate that the molecule is experiencing nearly free end-over-end rotation in the solid phase. Removal of the oxygen containing impurities frees the spectrum of $NO_{2}$, HNO and OH and makes it possible to extend the region of absorption somewhat farther than in the gas. In addition to the three strong HNO bands found by flash photolysis, the low temperature spectrum reveals three other weak bands which fit well into the upper state vibrational pattern. A weak absorption band at $30466 cm^{-1}$ attributed tentatively to trapped NH in the metastable $^{1}\Delta$ electronic state. The effective path of NH is so long that for the first time the extremely weak ${v}^{\prime} 1\longleftrightarrow {v}^{\prime}^{\prime}=0$ band of the triplet system has been observed. Broader absorption is observed for the $C_{2}$ Swan bands and the blue-shifted 4315A and red-shifted 3889A systems of CH.”
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Author Institution: Department of Chemistry, The Johns Hopkins University