Abstract
Density functional theory (DFT), Møller–Plesset (MP2) and coupled cluster with single and double substitutions including non-iterative triple excitations (CCSD(T)) calculations on the anions MX4−, with M = C, Si, Ge and X = F, Cl, Br, show that GeF4−, SiCl4−, GeCl4− and SiBr4− prefer a C2v conformation, but CCl4− is an elongated C3v structure. CBr4− has Td symmetry in MP2, but is slightly more stable in elongated C3v form with DFT and CCSD(T). GeBr4− has Td symmetry. CF4− and SiF4− are unstable with respect to loss of an electron. Vertical electron affinities (EAs) are negative also for CCl4 and SiCl4, and close to zero for GeF4 and SiBr4. Adiabatic EAs range from 0.47 eV for SiCl4 to 1.78 eV for GeBr4. The lowest excited states at Td symmetry are 2T2 resonances with energies of 2.1–3.5 eV, resulting from excitation of the a1 singly occupied molecular orbital to vacant t2 orbitals. Vertical excitation energies (VEEs) and vibrational frequencies are given for the most stable anionic geometries. Comparison with experimental VEEs for CCl4− is made. From dissociation energies of MX4, MX4−, MX3 and MX3−, appearance energies of X−, MX3−, X2− and MX2− were calculated. Most were found to be in reasonable agreement with experimental values. Theoretical spin densities and g-factors have been compared with experimental results available for CCl4−, SiCl4− and GeCl4−.
Acknowledgements
The author thanks Dr Pablo J. Bruna for reading the manuscript, and for making valuable comments and suggestions. Provision of computing facilities by ACE-net is gratefully acknowledged.
Supplemental data
Supplemental data for this article can be accessed http://dx.doi.org/10.1080/00268976.2014.976601.