The following ions [UO 2 (NO 3 Ϫ were generated from respective salts (UO 2 (NO 3 ) 2 , UO 2 (ClO 4 ) 3 , UO 2 (CH 3 COO) 2 ) by laser desorption/ionization (LDI). Collision induced dissociation of the ions has led, among others, to the formation of UO 4 Ϫ ion (m/z 302). The undertaken quantum mechanical calculations showed this ion is most likely to possess square planar geometry as suggested by MP2 results or strongly deformed geometry in between tetrahedral and square planar as indicated by DFT results. Interestingly, geometrical parameters and analysis of electron density suggest it is an U VI compound, in which oxygen atoms bear unpaired electron and negative charge. In the laboratory, the most common uranium compounds are the salts of uranyl (UO 2 2ϩ -U VI -containing cation), e.g., UO 2 (NO 3 ) 2 , UO 2 (CH 3 COO) 2 . Uranium compounds with this element at other oxidation states (other than IV and VI) are also known, however, they are less stable, e.g., the U V species in solutions easily undergo disproportionation reaction to U(IV) and U(VI) [2]. In nature, there are also uranyl peroxides UO 2 (O 2 ), but the respective minerals UO 2 (O 2 )(H 2 O) 2 and UO 2 (O 2 )(H 2 O) 4 do not exist in high abundances [3]. A number of more developed uranyl peroxides were obtained in labs [4 -7].Mass spectrometric studies of uranyl salts (mainly UO 2 (NO 3 ) 2 ) have been reported, first by using FAB (fast atom bombardment) as ionization method [8], and then by electrospray ionization [9 -15]. Most of the studies were performed in the positive ion mode; only Pasilis et al. have performed the ESI analysis in both positive and negative ion modes [10]. In this very excellent paper, the authors have systematically investigated the gasphase uranyl-containing ions and they have examined ligand association/exchange and H/D exchange reactions of the species, using FT-ICR mass spectrometry to obtain accurate mass measurements. In this communication, the collision induced dissociation (CID) of the ions [UO 2 (NOϪ is discussed. The ions were generated from respective salts (UO 2 (NO 3 ) 2 , UO 2 (ClO 4 ) 3 , UO 2 (CH 3 COO) 2 ) by laser desorption/ionization (LDI). As described further, the unusual formation of ion UO 4 Ϫ was detected upon decomposition of the ions subjected to CID. ExperimentalThe LDI mass spectra and LDI MS/MS spectra were obtained on a Waters/Micromass (Manchester, UK) Q-TOF Premier mass spectrometer (software MassLynx ver. 4.1; Manchester, UK) fitted with a 200 Hz repetition rate Nd/YAG laser ( ϭ 355 nm, power density 10 7 W/cm 2 ). For MS/MS experiments, argon was used as a collision gas at the flow-rate 0.5 mL/min in the collision cell. Collision energy (CE -the most important parameter for MS/MS experiments) is indicated in each MS/MS spectrum presented further.To prepare the target spots, 1 L of methanol solution containing uranyl salts was used (the concentration was of about 0.1 mol/dm [3]. After a few min at room temperature, the spot was dry and LDI mass spectra could be recorded. If the concentra...

No abstract