Coulomb-explosion

According to the ion-evaporation model, the droplets become smaller until a point is reached at which the surface charge is sufficiently high for direct ion evaporation into the gas phase to occur. In the case of the charge-residue model, repeated Coulombic explosions take place until droplets are formed that contain a single ion. Evaporation of the solvent continues until an ion is formed in the vapour phase. 

Coulombic explosion The process by which a droplet disintegrates into a number of smaller droplets which occurs when the repulsive forces between charges on the surface of a droplet are greater than the cohesive force of surface tension. 

From other work on Pb(CH3)4 it is known that an Auger cascade connected with an L or M vacancy in the lead atom leads to the development of a charge of up to -t-17. This results in the total destruction of the molecule through a Coulomb explosion. On the basis of the 4/5 rule and the 14% internal conversion, one can estimate that for Pb(CH3)4 the molecule should remain intact in at least 69% of the decays, corresponding to the transformation ... 

When an excited state is converted by ejection of an atomic electron, a high positive charge can be produced through subsequent Auger electron emission. Within the period of molecular vibration this charge is spread throughout the molecule to all atoms, and a Coulomb explosion results. This primary phenomenon occurs, of course, not only as a result of [ decay, but must be taken into account in all cases of nuclear reaction when deexcitation by inner electron conversion occurs... 

Relative Abundances and Energies of Ions Produced by the Coulomb Explosion of Pb(CH3)4 ... 

Coulomb Explosion and the Production of High Charge State Ions... 

Figure 11. Average ion kinetic energies as a function of cluster size for ammonia clusters and deuterated ammonia clusters resulting from Coulomb explosion of clusters. The average kinetic energies are obtained from the splittings in the cluster ion time-of-flight peaks see Figure 10. Taken with permission from ref. 90.

Figure 12. Coulomb explosion of hydrogen iodide clusters. Note the formation of l+ a small signal probably attributable to l+17 is seen in some experiments. Taken with permission from ref. 92.

Fig. 11.5. Diagram illustrating the components of an ESI source. A solution from a pump or the eluent from an HPLC is introduced through a narrow gage needle (approximately 150 pm i.d.). The voltage differential (4-5 kV) between the needle and the counter electrode causes the solution to form a fine spray of small charged droplets. At elevated flow rates (greater than a few pl/min up to 1 ml/min), the formation of droplets is assisted by a high velocity flow of N2 (pneumatically assisted ESI). Once formed, the droplets diminish in size due to evaporative processes and droplet fission resulting from coulombic repulsion (the so-called coulombic explosions ). The preformed ions in the droplets remain after complete evaporation of the solvent or are ejected from the droplet surface (ion evaporation) by the same forces of coulombic repulsion that cause droplet fission. The ions are transformed into the vacuum envelope of the instrument and to the mass analyzer(s) through the heated transfer tube, one or more skimmers and a series of lenses.

The new model has also been applied to the calculation of thermally averaged probability density functions for the out-of-plane inversion motion of the CH and H3O ions [9]. Such probability densities can be obtained experimentally by means of Coulomb Explosion Imaging (CEI) techniques (see, for example, Refs. [10,11]), and the results in Ref. [9] will be useful in the interpretation of the resulting images, just as analogous calculations of the bending probability distribution for the CHj ion were instrumental in the interpretation of its CEI images (see Refs. [9,12] and references therein). 

Fig. 1 The macroscopic and microscopic ESI process. The enlarged inset shows the droplet formation and subsequent Coulomb explosions.

Figure 14.2 Principle of electrospray ionization, (a) The analyte is dissolved in an appropriate solvent and sprayed via a capillary into an electric field. Here, the liquid filament finally forms charged droplets, (b) The solvent of the charged droplets evaporates, resulting in an increase of the surface charge up to a critical boundary, at which a Coulomb explosion occurs. The newly formed droplets undergo the same process. The final products are the desolvated, naked ions, which are then entering the mass spectrometer.

In large clusters do you observe new fragmentation pathways due to Coulomb explosion as observed in the nice experiments of Castleman s group ... 

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