Infrared spectra of the hydrogen-bonded pi complex C2H4–HF in solid argon

Abstract

The hydrogen‐bonded pi complex C₂H₄‐‐HF has been prepared by codeposition of C₂H₄ and HF with excess argon at 12 K. Isotopic substitution in both submolecules identified the complex and provided assignments to ν_s at 3731 cm⁻¹, ν_l at 424 and 396 cm⁻¹, and ν₇^c at 973 cm⁻¹. The observation of a substantial perturbation on the out‐of‐plane bending mode of the C₂H₄ submolecule in the complex without a perturbation on the in‐plane bending mode indicates that H–F is bonded to the pi electron system perpendicular to the plane of the molecule. The positions of ν_s and ν_l indicate a hydrogen bond of intermediate strength and the splitting in ν_l is characteristic of the anisotropy in the hydrogen bonding interaction with a π system.