title: Infrared spectra of the Cl- -C2H4 and Br- -C2H4 anion dimers.
abstract: 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.
authors.affiliation: School of Chemistry, University of Melbourne, Parkville, 3010, Victoria, Australia.
authors.forename: R L
authors.initials: RL
authors.lastname: Wilson
authors.forename: Z M
authors.initials: ZM
authors.lastname: Loh
authors.forename: D A
authors.initials: DA
authors.lastname: Wild
authors.forename: C D
authors.initials: CD
authors.lastname: Thompson
authors.forename: M D
authors.initials: MD
authors.lastname: Schuder
authors.forename: J M
authors.initials: JM
authors.lastname: Lisy
authors.forename: E J
authors.initials: EJ
authors.lastname: Bieske