Infrared spectra of molecular ions derived from the hydrogen and methyl halides trapped in solid neon

Abstract

A number of molecular ions have been stabilized in solid neon in sufficient concentration for detection of their infrared spectra. The neon matrices were prepared by codepositing the ion precursor, diluted in an excess of neon, at approximately 5 K with a beam of excited neon atoms. The results of these experiments are surveyed, and the studies of the hydrogen halides (X=Cl, Br, I) and methyl halides (X=F, Cl, Br) are described in greater detail. The position of the ν 2 + absorption of uncharged (HX) 2 is exceptionally sensitive to the matrix material. Rotation of simple hydrides, including H 2O, HX, and CH 3, in solid neon is inhibited by the electric field associated with the presence of ions. The fundamental absorptions of HX + in the neon matrix lie near the gas-phase band centers. Absorptions of (HX) 2 + are also identified, and the XHX − anion contributes to the infrared spectrum. In studies of the methyl halides, infrared absorptions of both the conventional (CH 3X +) and the ylidion (H 2CXH +) isomers are identified and assigned with the aid of ab initio calculations. The conventional structure is significantly distorted from threefold symmetry by Jahn–Teller interaction.