Infrared spectra of mass-selected Al+_(CH4)nN=1-6clusters

Authors

B L. J Poad, University of WollongongFollow
C D. Thompson, University Of Melbourne
E J. Bieske, University Of Melbourne

RIS ID

72190

Publication Details

Poad, B. L. J., Thompson, C. D. & Bieske, E. J. (2008). Infrared spectra of mass-selected Al+_(CH4)nN=1-6clusters. Chemical Physics, 346 (1-3), 176-181.

Abstract

Infrared spectra are recorded for Al⁺–(CH₄)_n n = 1–6 clusters in the CH stretch region (2800–3100 cm⁻¹). The spectra, which are obtained by monitoring photofragmentation in a tandem mass spectrometer, are dominated by a single, narrow band corresponding to the totally symmetric C–H stretching mode of the CH₄ subunits (rendered infrared active through the interaction with the Al⁺ cation). This band shifts progressively to higher wavenumber as the clusters becomes larger, concomitant with a weakening of the intermolecular Al⁺⋯CH₄ bonds. Supporting ab initio calculations for the n = 1–6 clusters at the MP2/aug-cc-pVDZ level indicate that the Al⁺ cation is attached to each CH₄ sub-unit in a face-bound η₃ configuration and that when possible the methane molecules are adjacent to one another. Clusters built around an inserted [H–Al–CH₃]⁺ core are also predicted to be stable but lie higher in energy than clusters built around an Al⁺ core; the latter species are the only ones observed experimentally.