Infrared spectra of the Cl−–C2H4 and Br−–C2H4 anion dimers

R.L. Wilson, Z.M. Loh, Duncan Wild, C.D. Thompson, M.D. Schuder, J.M. Lisy, E.J. Bieske

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7 Citations (Scopus)


Infrared spectra of mass-selected Cl−–C2H4 and Br−–C2H4 complexes are recorded in the vicinity of the ethylene CH stretching vibrations (2700–3300 cm−1) using vibrational predissociation spectroscopy. Spectra of both complexes exhibit 6 prominent peaks in the CH stretch region. Comparison with calculated frequencies reveal that the 4 higher frequency bands are associated with CH stretching modes of the C2H4 subunit, while the 2 weaker bands are assigned as overtone or combinations bands gaining intensity through interaction with the CH stretches. Ab initio calculations at the MP2/aug-cc-pVDZ level suggest that C2H4 preferentially forms a single linear H-bond with Cl− and Br− although a planar bifurcated configuration lies only slightly higher in energy (by 110 and 16 cm−1, respectively). One-dimensional potential energy curves describing the in-plane intermolecular bending motion are developed which are used to determine the corresponding vibrational energies and wavefunctions. Experimental and theoretical results suggest that in their ground vibrational state the Cl−-C2H4 and Br−-C2H4 complexes are localized in the single H-bonded configuration, but that with the addition of modest amounts of internal energy, the in-plane bending wavefunction also has significant amplitude in the bifurcated structure.
Original languageEnglish
Pages (from-to)3419-3425
JournalPhysical Chemistry Chemical Physics
Issue number19
Publication statusPublished - 2005


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