The Infrared Spectrum of the Hydrogen-Bonded Molecule Dimethyl Ether … Hydrogen Chloride in the Gas Phase

Abstract

A detailed study of the infrared spectra of (CH₃)₂O … HCl and its isotopic modifications is presented. The hydrogen-bond stretching mode occurs at 119 ± 4 cm⁻¹ in (CH₃)₂O … HCl, (CD₃)₂O … HCl, and (CH₃)₂O … DCl. The O … H—Cl deformation modes yield a band centered at 470 cm⁻¹, which is broad and complex. It is interpreted in terms of sum and difference transitions involving the HCl rocking modes, which are deduced to be at about 50 cm⁻¹. The O … D—Cl deformation band is centered at 360 cm⁻¹. A band at 790 cm⁻¹ in (CH₃)₂O … HCl and 600 cm⁻¹ in (CH₃)₂O … DCl is assigned to the overtone of the deformation modes. The shapes of the bands due to the ethereal modes in the molecule can not indicate the molecular geometry and do not agree with the shapes calculated from reasonable moments of inertia. The temperature dependence of the band due to the HCl stretching mode indicates that the fundamental transition is at 2480 cm⁻¹, not at 2574 cm⁻¹ as previously postulated. The DCl stretching band in (CH₃)₂O … DCl has a different shape to that in (CD₃)₂O … DCl. The differences are attributed to combination transitions involving the ethereal modes. It is suggested that the DCl and HCl stretching modes interact with the DCl or HCl rocking modes, thus causing shoulders 50 cm⁻¹ away from the DCl stretching fundamental, and contributing to the general diffuseness of the HCl stretching band. The relative intensities of the bands due to (CH₃)₂O … HCl are presented.