Structures of F - -(CH4)n and Cl - -(CH4)n (n = 1,2) Anion Clusters Elucidated through Ab Initio Calculations and Infrared Spectra

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.

Communication: Probing the entrance channels of the X + CH4 → HX + CH3 (X = F, Cl, Br, I) reactions via photodetachment of X−–CH4

“…1 and discussed in detail later. For Cl-CH 4 system, previous work showed that the anion equilibrium geometry overlaps with that of the vdW complex in the reactant valley, 23,24,28 which was confirmed by the slow electron velocity-map imaging (SEVI) spectrum of Cl − -CH 4 reported by Neumark.…”

Infrared studies of ionic clusters: The influence of Yuan T. Lee

“…Other mass spectrometric approaches are also possible. These often involve anions solvated by water, 46,71 methane, 72 or ethylene. 58,59 Tunable infrared laser sources are the third key element in this field of research.…”

Anticooperativity of FH···Cl− hydrogen bonds in [FH)nCl]− clusters (n = 1…6)

“…Geometric anticooperativity of FH···F − hydrogen bonds was studied computationally and experimentally by H/D isotope effects on 1 H and 19 F NMR chemical shifts . Apart of rather extensive literature on aqueous solutions of halide anions, other types of clusters of solvated negative ions are also discussed in literature—[(H 2 O) 2 Cl] − , [(H 2 O) 2 Br] − , [(H 2 O) 2 I] − , [(FH) n Cl] − , [(C 2 H 2 ) n Cl] − ( n = 1…9), [(C 2 H 2 ) n Br] − , [(C 2 H 2 ) n I] − , [(D 2 ) n Cl] − , [(D 2 ) n F] − , [(CH 4 ) n Cl] − , [(CH 4 ) n F] − , Cl − complexes with several CHCl 3 , CH 2 Cl 2 and CH 3 Cl molecules in crystal hydrates, and so forth.…”