Structures of F−-(CH4)n and Cl−-(CH4)n (n = 1,2) Anion Clusters Elucidated through Ab Initio Calculations and Infrared Spectra
Zoë M. Loh A , Rosemary L. Wilson A , Duncan A. Wild A , Evan J. Bieske A C and Mark S. Gordon BA School of Chemistry, University of Melbourne, Melbourne VIC 3010, Australia.
B Department of Chemistry, Iowa State University, Ames, IA 50011, USA.
C Corresponding author. Email: evanjb@unimelb.edu.au
Australian Journal of Chemistry 57(12) 1157-1160 https://doi.org/10.1071/CH04149
Submitted: 21 June 2004 Accepted: 20 August 2004 Published: 8 December 2004
Abstract
Ab initio calculations are performed at the MP2/aug-cc-pVTZ level for F−-CH4 and Cl−-CH4, to show that the dimers have C3v symmetry with the CH4 sub-unit attached to the halide anion by a single hydrogen bond. This geometry is consistent with infrared spectra of F−-CH4 and Cl−-CH4 recorded in the CH-stretch region. The calculations also indicate substantial anharmonicity in the H-bonded CH stretch of F−-CH4. Infrared spectra of the F−-(CH4)2 and Cl−-(CH4)2 trimer clusters are consistent with structures that have two equivalent CH4 sub-units H-bonded to the halide core. Additional bands in the F−-(CH4)2 spectrum are assigned as transitions to CH4 bending overtone and combination levels, gaining infrared intensity from Fermi interaction with the H-bonded CH stretch.
Acknowledgments
We thank the Australian Research Council and the University of Melbourne for support.
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