Transfer of translational energy

If charge exchange occurs when the incident positive ion passes the neutral gas molecule with a certain velocity, transfer of translational energy will usually take [place. This transfer of translational energy... 

If no transfer of translational energy occurs, then the charge exchange process probably takes place when the distance between the ion and the molecule is large. This means, however, that the ion and the molecule can be considered as isolated from each other, and therefore, the recombination process of the ion and the ionization process of the molecule must obey the spectroscopic transition laws. On the other hand, if a large transfer of translational energy takes place, then the process probably takes place when the distance is small, and possibly then all selection rules break down. 

The importance of the transfer of translational energy has been stressed by several authors (31, 48, 49, 50). The problem will be discussed below especially with regard to the difference in the results obtained in the perpendicular type apparatus in Stockholm and the longitudinal type apparatus in Chicago. 

If a charge exchange process, A + + B- A -f- B +, occurs when the distance between the two particles is large, we expect that no transfer of translational energy takes place in the reaction and that the same selection rules govern the ionization as in spectroscopic transitions. This means that if the molecule B is in a singlet state before the ionization, the ion B + will be formed in a doublet state after ionization of one electron without rearrangements of any other electrons, at least for small molecules. 

The use of Eqs. (30) and (31) was criticized by Hupp and Weaver [131], because these equations imply that the activation occurs only by the transfer of translational energy. However, in the condensed phase the activation may occur through solvent polaron fluctuations and the transfer of oscillation energy of solvent molecules in the bulk to solvent molecules in the immediate vicinity of the reactant or even to electronic levels of the reactant [105, 132]. 

In a binary collision between hard-sphere molecules, what ratio of molecular masses results in the maximim transfer of translational energy What is AE /EjO for collision between hydrogen (A) and oxygen (B), each with a line-of-center velocity equal to one-half the average speed at 25°C (given in Table 2.2b) ... 

It is therefore important to avoid transfer of translational energy during the charge-exchange process. This can be done in a tandem mass spectrometer of perpendicular type, and therefore this type will be the only one that will be considered in detail in this chapter. 

If transfer of translational energy can be avoided, the energetics of the reaction can be expressed as... 

To avoid transfer of translational energy during the charge-transfer process, it is necessary to use slow incident ions and to extract and study Magnet A... 

The selection rules obviously break down if the charge exchange takes place at a very small distance between the colliding particles. In this case, however, transfer of translational energy will also probably take place. As the study of charge-exchange mass spectra in a tandem mass spectrometer of perpendicular type discriminates against such processes, the breakdown of the selection rules is probably without importance for our purposes. 

The question to what extent this goal can be attained has been discussed repeatedly. " Measurements performed in tandem machines with smaller discrimination or in tandem machines of longitudinal type gave results that indicated a considerable transfer of translational energy during the charge-exchange process. The problem was reviewed earlier and therefore only one example will be presented here which illustrates the difference between different machines. 

Table III. Transfer of Translational Energy in Charge-Exchange Processes"...

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