title: Infrared spectra and ab initio calculations for the F- -(CH4)n (n = 1-8) anion clusters.
abstract: Infrared spectra of mass-selected F- -(CH4)n (n = 1-8) clusters are recorded in the CH stretching region (2500-3100 cm-1). Spectra for the n = 1-3 clusters are interpreted with the aid of ab initio calculations at the MP2/6-311++G(2df 2p) level, which suggest that the CH4 ligands bind to F- by equivalent, linear hydrogen bonds. Anharmonic frequencies for CH4 and F--CH4 are determined using the vibrational self-consistent field method with second-order perturbation theory correction. The n = 1 complex is predicted to have a C3v structure with a single CH group hydrogen bonded to F-. Its spectrum exhibits a parallel band associated with a stretching vibration of the hydrogen-bonded CH group that is red-shifted by 380 cm-1 from the nu1 band of free CH4 and a perpendicular band associated with the asymmetric stretching motion of the nonbonded CH groups, slightly red-shifted from the nu3 band of free CH4. As n increases, additional vibrational bands appear as a result of Fermi resonances between the hydrogen-bonded CH stretching vibrational mode and the 2nu4 overtone and nu2+nu4 combination levels of the methane solvent molecules. For clusters with n < or = 8, it appears that the CH4 molecules are accommodated in the first solvation shell, each being attached to the F- anion by equivalent hydrogen bonds.
authors.affiliation: School of Chemistry, The University of Melbourne, Australia 3010.
authors.forename: Z M
authors.initials: ZM
authors.lastname: Loh
authors.forename: R L
authors.initials: RL
authors.lastname: Wilson
authors.forename: D A
authors.initials: DA
authors.lastname: Wild
authors.forename: E J
authors.initials: EJ
authors.lastname: Bieske
authors.forename: J M
authors.initials: JM
authors.lastname: Lisy
authors.forename: B
authors.initials: B
authors.lastname: Njegic
authors.forename: M S
authors.initials: MS
authors.lastname: Gordon