THEORETICAL AND MASS-SPECTROMETRIC INVESTIGATIONS OF THE FORMATION OFCALCIUM-FLUORIDE CLUSTER IONS

The formation of CanFm+ cluster ions (n = 1-3, m = 1-4) was investigat ed by using two different plasma mass spectrometric methods: spark sou rce mass spectrometry and laser ablation inductively coupled plasma ma ss spectrometry. Both methods give similar abundance distributions of cluster ions, with a maximum ion intensity for the Ca2F3+ species. The se measurements were interpreted by theoretical calculations of the st ructures and formation energies of different cluster ions CanFm+, with in density functional theory, using a self-consistent held linear comb ination of atomic orbitals method. We discuss the possible reaction ch annels of the cluster formation and find that the formation energies o f the clusters correlate with the intensities of the CanFm+ ions. Qual itatively, clusters with closed electronic shells - in particular, CaF + and Ca2F3+ - are especially stable (''magic'' clusters) and show a h igh abundance in the mass spectrum. (Int J Mass Spectrom 176 (1998) 10 3-111) (C) 1998 Elsevier Science B.V.