Endothermic ion-molecule reactions

The choice of a particular type of gas discharge for quantitative studies of ion-molecule reactions is essential if useful information is to be obtained from ion abundance measurements. Generally, two types of systems have been used to study ion-molecule reactions. The pulsed afterglow technique has been used successfully by Fite et al. (3) and Sayers et al. (1) to obtain information on several exothermic reactions including simple charge transfer processes important in upper atmosphere chemistry. The use of a continuous d.c. discharge was initiated in our laboratories and has been successful in both exothermic and endothermic ion-molecule reactions which occur widely within these systems. 

Theory. The requirement of a threshold energy for an endothermic ion-molecule reaction can be used together with the described model to calculate the exact position within the dark space where an ion can undergo reaction having gained from the field at least the necessary... 

Photoionization has been most successfully applied to study of the effects of reactant vibrational energy on the cross sections of exothermic and endothermic ion-molecule reactions. Reactions studied by this method are summarized in Table II. In addition, photoionization methods... 

An example of the endothermic ion—molecule reactions in which translational kinetic energy is converted into internal energy rather efficiently at low collision velocities is... 

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. 

W.B. Maier II, Atom transfer in endothermic ion-molecule reactions, J. Chem. Phys. 46, 4991-4992 (1967). 

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