Endothermic collision-induced dissociation

In several of the studies of fluorlnated alkanes endothermic collision-induced dissociations of the reactant Ions were also observed. It was suggested that when a... 

The results given j in Table j II show that in perfluorlnated propylene, fragment CF and CF Ions undergo exothermic F transfer reactions with the parent molecule. The only other reactions observed In C Fg as well as In 2-C,Fg (5) are endothermic collision-Induced dissociation reactions. 

Fragmentation occurs because the repeller voltage increases the kinetic energy of the ions, not only making collision-induced dissociation (CID) more likely but also allowing endothermic ion-molecule and solvent-switching reactions to occur. 

The determination of thermochemistry using threshold collision-induced dissociation (TCID) relies on a deceptively simple experiment determine the energy threshold for the endothermic reaction (Eq. 1), the dissociation of the molecular ion AB+ ... 

We have studied [11] collisions of state-selected H2(v) ions with He to give (see Eq. 3) HeH+ + H (chemical reaction) and He + H+ + H (collision-induced dissociation — CID) at a relative collision energy of 3.1 eV. Individual vibrational levels between 0 and 6 were studied. The cross sections were put on an absolute scale by normalizing to the earlier work of Chupka and coworkers [24], Both product channels are endothermic for H (v = 0) ions, chemical reaction by 0.81 eV and CID by 2.65 eV. Thus, one expects vibrational excitation of the reactant ions to greatly increase the cross sections for both products. This is confirmed by our results. Absolute cross sections for HeH+ products are shown in Fig. 7 and for the H + products in Fig. 8. 

Efficient conversion of translational kinetic energy into internal energy has also been discovered for endothermic processes other than atom transfer, such as charge transfer [176—179], dissociative charge transfer [94,176, 180,181] and collision-induced dissociation [98, 169]. 

Collision-induced dissociation mass spectrum of the proton-bound dimer of isopropanol [( 1 3)2 CH0H]2lf ". The miz 121 ions were first isolated in the trap, followed by resonant excitation of their trajectories to produce CID. Fragment ions include water loss mIz 103), loss of isopropanol mIz 61) and loss of 42 amu mIz 79). (b) Ion-molecule reactions in an ion trap. In this example the miz 103 ion was first isolated and then resonantly excited in the trap. Endothermic reaction with water inside the trap produces the proton-bound cluster at miz 121, while CID produces the fragment with m z 61. 

ICR-FTMS experiments have been employed to derive thermodynamic information using several approaches ( ). These include studies of exothermic and endothermic ion-molecule reactions, equilibration studies, competitive collision-induced dissociation reactions, and photodissociation studies. Exothermic reactions involving therma-lyzed (cooled by an inert buffer gas) ions provide brackets on metal-ligand bond enthalpies, as illustrated by Equation 44 which implies that D(Fe-C5H4 ) > 66 kcal/mol. Endothermic reactions can also be studied in the manner described above for ion beam experi-... 

In this review we discuss five techniques involving Fourier transform mass spectrometry (FTMS) for determining qualitative and quantitative metal ion-ligand bond energies. These include (i) exothermic ion-molecule reactions, (ii) equilibrium measurements, (iii) competitive collision-induced dissociation, (iv) endothermic ion-molecule reactions, and (v) photodissociation. A key advantage of the FTMS methodology is its ion and neutral manipulation capabilities which permit the formation and study of a limitless number of interesting metal-ion systems. 

It is interesting that the NO /NO interaction yields O as a product by a rearrangement process such as reaction (27), but that N production by the analogous reaction (26) does not occur. As already noted, the endo-thermicities of both reactions (26) and (27) are well below the energy requirements of the collision-induced dissociations. However, reaction (26) is 2.7 eV more endothermic than reaction (27) and may not be observed simply because it cannot compete effectively with the lower-energy decomposition path. 

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