Infrared Spectrum of the ClHCl− Ion Isolated in an Argon Matrix

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Abstract
Upon vacuum‐ultraviolet photolysis at 14°K of samples of HCl isolated in an argon matrix at mole ratios favorable for the presence of an appreciable concentration of dimeric HCl, prominent absorptions appear at 696 and 956 cm−1. The positions, contours, and relative intensities of these absorptions correspond within experimental error with those previously attributed to the ClHCl free radical isolated in an argon matrix. Studies of a chlorine‐37 enriched sample have confirmed the presence of two chlorine atoms in the molecule. A broad, unstructured absorption at 2870 Å may also be contributed by this ClHCl species. When a small concentration of atomic potassium or cesium is codeposited with the Ar:HCl sample, evidence is obtained for the formation of an alkali‐metal‐containing complex. Photoionization of the alkalimetal atoms upon exposure of the resulting sample to the radiation of a medium‐pressure mercury arc leads to the appearance of very prominent absorptions at 696 and 956 cm−1. It is proposed that these absorptions may more suitably be assigned to the ClHCl− ion, trapped in an inert, essentially nonionic environment. Implications of this reassignment with regard to the nature of the hydrogen bonding of ClHCl− are discussed, and possible mechanisms for the production of ClHCl− under the conditions of these experiments are considered.