Dissociation of doubly charged clusters of lithium acetate: Asymmetric fission and breakdown of the liquid drop model

Abstract

Electrospray ionization (ESI) results in the formation of multiply charged cluster ions which then fragment via two competing processes: fission (charge separation) via Coulomb repulsion, and evaporation of one or more neutrals from the fragmenting ion, as described by Rayleigh's liquid drop model. Unimolecular and collision-induced dissociation (CID) of doubly charged lithium acetate clusters, (CH3 COOLi)n Li2 (2+) , demonstrated that Coulomb fission via charge separation is the dominant dissociation process with no contribution from the neutral evaporation processes for all such ions from the critical limit to larger cluster ions, although the latter process was normally observed in most earlier studies of multiply charged clusters. Doubly and higher charged lithium acetate cluster ions were generated by ESI. Unimolecular and CID of mass selected doubly charged cluster ions above the critical limit were recorded at high resolution using an LTQ Velos Orbitrap mass spectrometer. Unimolecular and collision-induced dissociation of doubly charged lithium acetate clusters proceed via symmetric fission processes and the intensity of the fragment ions decreases as the cluster size increases. Dissociations via neutral evaporation of a monomer or larger clusters are not observed. Doubly charged clusters of lithium acetate above the critical limit dissociate via symmetrical fission processes and not neutral evaporation. These results are clearly in disagreement with the Rayleigh liquid drop model that has been used previously to predict the critical size and explain the fragmentation behavior of multiply charged clusters. Copyright © 2016 John Wiley & Sons, Ltd.