Dimers of alkaline earth metal halide radicals, (MX)(2) (M=Be, Mg, Ca; X=F, Cl): A theoretical study

Alkaline earth metal halide radical dimers, (MX)(2) (M = Be, Mg, Ca and X = F, Cl) have not yet been observed experimentally and their existence could be doubted since MX is known to disproportionate in the bulk. We study the (MX)2 species using DFT and MP2 methods and show that they are either ther modynamically or kinetically stable with respect to various reactions inclu ding disproportionation. Energetics, geometries, and vibrational frequencie s of sing let and triplet equilibrium structures and some transition states are calculated. The ground states of (MX)(2) are all singlet except (CaF)( 2) which is triplet and, with the possible exception of(CaF)(2), the ground states have a rhombic structure in which the X atoms are shared equally wi th each M atom. The ionization potentials of the (MX)(2) species are signif icantly lower than those of the corresponding MX species suggesting that th eir chemistry may be significantly different. (C) 2001 American Institute o f Physics.