Metastability of isolated platinum and palladium tetrahalide dianions and the role of electron tunneling

In the present study we have isolated MX42- (M = Pd, Pt; X = Cl, Br) in a r oom temperature Penning trap under virtually collision-free, ultra high vac uum conditions and have probed for metastable decay on a time scale of up t o 1000 s. While PdCl42-, PdBr42- and PtBr42- do not react appreciably on th is time scale, PtCl42- undergoes tunneling electron loss to form PtCl4-; wi th a half-life of 5 s. We provide kinetic data and ab-initio quantumchemica l calculations of relevant initial and final states as well as Coulomb barr iers. All four species are metastable towards halide loss on the basis of t hese calculations. (C) 2000 Elsevier Science B.V; All rights reserved.