Coulomb explosion mechanism

To emphasize this point, the Coulomb explo sion mechanism is defined in the following terms. The Coulomb explosion mechanism for fragmentation... 

The alternative mechanism, the ion-evaporation model, was proposed initially by Iribarne and Thomson13 (Fig. 4) and involves desolvation of the droplets, producing an increase in charge density over the droplet surface that causes coulombic explosion and eventually leads to ejection of individual ions. 

Fig. 1.7. Two-dimensional Api2-0i2 correlation map for the three-body Coulomb explosion of CS + at a field intensity of 0.2PW/cm2. A logarithmic intensity scale is used to emphasize weak features. The solid curve represents the trajectory obtained from classical mechanical calculations for the sequential explosion pathway. The open circles represent the values for five rotational angles,

Mechanisms of molecular ion formation and fragmentation applicable to organic molecules is shown in Fig. 2.7. a) Molecular-ion formation will be dominant, provided the excitation wavelength is non-resonant with the electronic absorption of the molecular cation. Multiply charged ions are produced, and eventually lead to a Coulomb explosion even with an intensity level of 1014 Wcm 2. On the other way (Fig. 2.7b), fragmentation is vigor-... 

In cases where the yield of molecular ions is higher than 10% and where the fragmentation pattern depends upon the atomic site of the core hole, the dissociation processes clearly depend upon the electronic structure of the molecule and the details of the electronic relaxation, i.e. not all pathways produce essentially the same result. The mechanism then may involve vibrational dissociation or electronic or vibrational predissociation as well as direct dissociation. Even in these cases, some of the electronic relaxation channels may rupture all the bonds in a molecule and high-kinetic-energy fragments can be produced. Such channels sometimes are labeled a Coulomb explosion, but this terminology should not be confused with the more specific use of the term that is proposed above. 

For very short pulses, an additional mechanism called Coulomb explosion was reported recently [27]. It could be shown that dielectrics (in contrast to metals and semiconductors) are strongly charged at the surface on a femtosecond time scale and undergo an impulsive explosion. 

Figure 13.15 LC-MS interface ionization mechanism diagrams, (a) coulomb explosion in ESI droplets and (b) reactions leading to molecular ion in APCI. (Adapted with permission from Applied Biosystems/MDS Sciex.)...

Fig. 10.2 Principle of ionisation source and at atmospheric pressure. The charged aerosol is mechanism of gaseous ion formation in ESI- evaporated due to Coulomb explosions to MS. The sample solution is admitted through a smaller droplets which finally result in desol-small capillary from which the spray is formed vated macro-ions.

The charges, with the signs opposite to the sign of the electric potential applied to the MS inlet, accumulate on the liquid meniscus at the capillary outlet. This process is followed by the formation of a Taylor cone and Coulomb explosions which lead to the formation of fine droplets. The mechanism responsible for generation of charged droplets and ions in Pl-ESI appears to be similar to that found in the conventional ESI process (Section 2.4). 

The CTMC calculations give a physical insight into possible mechanisms for the reason that antiprotons are much more efficient at ionizing helium than protons. A Coulomb explosion is seen to occur when the antiprotons pass between the electrons and the nucleus. For distant collisions the antiproton is seen to knock the nearest electron towards the further one, but protons pull the nearest electron away from the far one. Vegh has also proposed a similar, if more complicated, model depending on the radial coupling between the electrons [7.17]. 

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