Bonding energetics in clusters formed by cesium salts: a study by collision-induced dissociation and density...

In relation to the interaction between (137)Cs and soil organic matter, electrospray mass spectrometry experiments and density functional theory (DFT) calculations were carried out on the dissociation of positively charged adducts formed by cesium nitrate and cesium organic salts attached to a cesium cation [Cs(CsNO(3))(CsA)](+) (A = benzoate, salicylate, hydrogen phthalate, hydrogen maleate, hydrogen fumarate, hydrogen oxalate, and hydrogen malonate ion). These mixed clusters were generated by electrospray from methanol solutions containing cesium nitrate and an organic acid. Collision-induced dissociation of [Cs(CsNO(3))(CsA)](+) in a quadrupole ion trap gave [Cs(CsNO(3))](+) and [Cs(CsA)](+) as major product ions. Loss of HNO(3) was observed, and also CO(2) loss in the case of A = hydrogen malonate. Branching ratios for the dissociation into [Cs(CsNO(3))](+) and [Cs(CsA)](+) were treated by the Cooks' kinetic method to obtain a quantitative order of bonding energetics (enthalpies and Gibbs free energies) between Cs(+) and the molecular salt (ion pair) CsA, and were correlated with the corresponding values calculated using DFT. The kinetic method leads to relative scales of Cs(+) affinities and basicities that are consistent with the DFT-calculated values. This study brings new data on the strong interaction between the cesium cation and molecular salts CsA.