Metastable dissociation of doubly charged carbon dioxide cluster ions

Abstract

Multiply charged CO/sub 2/ cluster ions are produced by adiabatic nozzle expansion and subsequent ionization by electron impact. They are analyzed in a double focussing sector field mass spectrometer (reversed geometry). (CO/sub 2/)/sub n//sup 2 +/ cluster ions are only detected above an electron energy of about 30 eV and with sizes n greater than or equal to 45 in the direct mass spectrum. Metastable decay reactions of these ions occurring in the first field free region are investigated by decoupling the analyzer fields. It is shown that (CO/sub 2/)/sub n//sub 2//sup +/ with sizes of n greater than or equal to 44 lose one neutral monomer or, roughly ten times less probable, two neutral monomers in these dissociation reactions. The total effective dissociation rates for these dissociation processes are very large, e.g. approx.2 x 10/sup 4/ s/sup -1/ for (CO/sub 2/)/sub 47//sup 2 +/. Conversely, no singly charged fragment ions were observed to be produced by Coulomb explosion from doubly charged clusters in the first field free region. Moreover, besides doubly charged stoichiometric ions the existence of doubly charged fragment cluster ions with n greater than or equal to 44 in observed in the mass spectra.