The Cl--CH4 anion dimer: mid infrared spectrum and ab initio calculations

The Cl--CH4 dimer has been investigated using infrared vibrational predisso ciation spectroscopy (2800-3080 cm(-1) range), and through ab initio calcul ations at the MP2(full)/aug-cc-pVTZ level. The infrared spectrum features p arallel and perpendicular bands, associated with excitation of C-H stretch vibrations localized on the CH4 core. Spectroscopic and theoretical data ar e consistent with a C-3v proton-bound minimum energy configuration for the complex, although internal rotation of the CH4 sub-unit is not completely q uenched. The calculated barrier for tunneling between equivalent proton-bou nd minima is 603 cm(-1). Comparisons are made between the properties of the isoelectronic Cl--H2O, Cl--NH3, and Cl--CH4 complexes. (C) 2000 Elsevier S cience B.V. All rights reserved.