Both breakdown graphs and energy-dependent (ED) maps provide a means of visually representing the fragmentation processes resulting from collision-induced dissociation at different energies. The two presentation methods may be combined for a complete picture of the appearance, disappearance and maximum abundance collision potentials of each of the ions involved in the fragmentation process. A demonstration of this approach is presented using two very different classes of compound, an amino acid and a transition metal carbonyl cluster. Copyright # 2002 John Wiley & Sons, Ltd.Electrospray ionisation mass spectrometry (ESI-MS) is an enormously versatile analytical technique, allowing the collection of molecular weight data on a huge range of compounds hitherto inaccessible to mass spectrometry. 1Modern electrospray mass spectrometers also incorporate means of fragmenting ions produced in the ESI process, usually by collision-induced dissociation (CID) 2 either at the skimmer cone, in a collision cell or inside an ion trap or FTICR cell. 3 The extent of CID can be smoothly varied depending on the degree of fragmentation required, and the resulting ions provide useful structural information. A huge amount of data may be gathered in this way, and we have recently introduced the technique of energy-dependent electrospray ionisation mass spectrometry (EDESI-MS) as a convenient means of presenting this data. 4 It essentially involves a 2D projection (collision energy vs. m/z) of a 3D surface (the 3rd dimension, ion intensity, is on the axis perpendicular to the paper). The major advantages of this method are concise illustration of the data from up to 200 spectra and easy visualisation of the fragmentation sequence. EDESI-MS is a comprehensive solution to the problem of data presentation compared with the traditional approach of a stacked series of selected spectra. 5 We have recently extended the technique to laser-desorption/ionisation mass spectrometry (EDLDI-MS), 6 and, in the MS/MS mode, the`energy-dependent' method of data presentation is equally applicable to any ionisation technique. Breakdown graphs (a plot of percentage fragment ion abundance vs. collision energy or cone voltage) have been used by Harrison and others to obtain energy-resolved fragmentation data from CID experiments at the skimmer cone or in the collision cell of electrospray ionisation mass spectrometers.7 These breakdown graphs represent an alternative way of depicting the same data presented in an EDESI map, and may be incorporated into the EDESI-MS presentation in a logical way by including a breakdown graph on the right-hand side of the map. This approach results in a degree of redundancy, as the data illustrated on the map is projected both onto the mass axis (the summation spectrum at the top of the map) and to the cone (or collision) voltage axis (the breakdown graph at the side of the map). Nonetheless, it does provide an aid to interpretation in much the same way as the standard spectra that are typically projected onto two axes of a...

The anionic clusters [HOs(5)(CO)(15)](-), [PtRu(5)C(CO)(15)](2-), [Os(10)C(CO)(24)](2-), [Os(17)(CO)(36)](2-), [Os(20)(CO)(40)](3-), [Co(6)C(CO)(15)](2-), [Pt(3)Ru(10)C(2)(CO)(32)](2-) and [Pd(6)Ru(6)(CO)(24)](2-) have been analysed by energy-dependent electrospray ionisation mass spectrometry (EDESI-MS). Three main features have emerged. Firstly, carbonyl ligands are fragmented from clusters with compact metal cores in an orderly fashion, with each of the ions generated by CO loss having approximately equal intensity. Secondly, electron autodetachment takes place in multiply charged anionic clusters, but only after elimination of a large proportion of their carbonyl ligands. Thirdly, clusters with open metal cores do not undergo CO loss in an orderly fashion, but certain peaks are considerably less intense. The appearance of these low-intensity peaks is believed to signify polyhedral core rearrangements, with open clusters folding to form more compact geometries. In some cases, the gas-phase transformations observed by EDESI-MS mirror those that are known to take place in solution.

Cluster reactivity in the gas phase has been probed extensively with clusters generated by using a variety of custombuilt sources. These include pulsed-laser vaporisation, continuous-operation ovens, fast-atom and secondary-ion sputtering, dc discharge, and pulsed-arc cluster-ion sources.[1] All generate an assortment of clusters of different nuclearities, and MS n techniques make selection of a particular sized cluster relatively straightforward. Both homo-and heteronuclear clusters are known.[2] All of these techniques employ a similar strategy to cluster synthesis; that is, the target is vaporised, the gas-phase metal atoms condensed, and the resulting clusters examined by mass spectrometry. We report herein an entirely different approach for the production of bare-metal gas-phase clusters, in which presynthesised transition-metal-carbonyl-cluster anions are delivered into the gas phase by a standard electrospray ionisation (ESI) source and stripped free of ligands by using collision-induced dissociation (CID) at the skimmer cone. The benefits of this approach are high yields of a specific cluster, no requirement for a special source, easy access to heteronuclear clusters and/ or those with interstitial atoms, and a vast library of known clusters to draw from.Because mixed-metal-carbonyl clusters are currently extensively used as precursors for metal nanoparticle catalysts (the clusters are absorbed inside mesoporous silica and calcined to remove the ligands), [3] examination of their gasphase reactivity may provide insight into their action as[*] Dr.

Three polynuclear transition metal carbonyl cluster anions, Ru3Co(CO)13−, Ru6C(CO)162−, and Ru6(CO)182− have been studied using energy-dependent electrospray ionization mass spectrometry (EDESI–MS) and photodetachment photoelectron spectroscopy (PES). EDESI–MS maps show a simple collision-induced dissociation (CID) process for Ru3Co(CO)n− by stripping CO down to the metal core. For the doubly charged species, two competing CID channels were observed, viz. loss of neutral CO and loss of CO+e−. It was found that the parent dianions first lose neutral CO down to n=9, producing a series of dianions, Ru6C(CO)n2− (n=9–16) and Ru6(CO)n2− (n=9–18). For n<9, the dianions become electronically unstable against autodetachment, and singly charged anions, Ru6C(CO)n− and Ru6(CO)n− (n=0–9), were observed. The PES spectra of the dianions show the electron binding energies decrease monotonically as n decreases and become ∼0.0 eV for n=9, in exact agreement with the CID patterns that reflect the electronic instability of the doubly charged metal complexes with n<9. All of the PES spectra show congested features, indicating very high density of low-lying electronic states for the transition metal carbonyl clusters. The electron binding energies of Ru3Co(CO)n− are similar for n=4–13, but decrease sharply from n=4 to 0. The intramolecular Coulomb repulsion in the dianions was observed to increase with loss of CO, ranging from ∼1.8 eV for Ru6C(CO)162− to ∼2.4 eV for Ru6C(CO)92−.

Cluster reactivity in the gas phase has been probed extensively with clusters generated by using a variety of custombuilt sources. These include pulsed-laser vaporisation, continuous-operation ovens, fast-atom and secondary-ion sputtering, dc discharge, and pulsed-arc cluster-ion sources.[1] All generate an assortment of clusters of different nuclearities, and MS n techniques make selection of a particular sized cluster relatively straightforward. Both homo-and heteronuclear clusters are known.[2] All of these techniques employ a similar strategy to cluster synthesis; that is, the target is vaporised, the gas-phase metal atoms condensed, and the resulting clusters examined by mass spectrometry. We report herein an entirely different approach for the production of bare-metal gas-phase clusters, in which presynthesised transition-metal-carbonyl-cluster anions are delivered into the gas phase by a standard electrospray ionisation (ESI) source and stripped free of ligands by using collision-induced dissociation (CID) at the skimmer cone. The benefits of this approach are high yields of a specific cluster, no requirement for a special source, easy access to heteronuclear clusters and/ or those with interstitial atoms, and a vast library of known clusters to draw from.Because mixed-metal-carbonyl clusters are currently extensively used as precursors for metal nanoparticle catalysts (the clusters are absorbed inside mesoporous silica and calcined to remove the ligands), [3] examination of their gasphase reactivity may provide insight into their action as[*] Dr.