Penning ionization processes

With the same apparatus the symmetrical systems He2, Ne2, Ar2 and Kr2 were studied.88 The prominent process in collisions between He-atoms at low energies, besides formation of negative excited He -ions, is the simultaneous formation of two excited He(lsnl)-atoms. When the atoms are still close together, molecular ionization very similar to a Penning ionization process occurs and accounts for the emission of electrons 88... 

In the second group of reactions are those between dielectric gas molecules and photons, produced by deexcitation of excited species at high E/N (such as AB and B in Table I and more likely, excited species produced by recombination processes). Here, three types of processes can increase the number of free electrons in the gas dielectric photoionization of AB (processes 8a and 8b), photoionization of the negative ions (photodetachment, process 10), and Penning ionization (process 11a or 11b, due to excited species produced via 7 or 3b, respectively). Of course, photons can collide with the electrodes and inject new electrons into the gas dielectric in this way. 

Penmman-Zoph process Penning discharge Penning gauge Penning ionization... 

Non-ionizing electron-neutral interactions create electronically excited neutrals. The ionization reactions occurring when electronically excited neutrals, e.g., noble gas atoms A, collide with ground state species, e.g., some molecule M, can be divided into two classes. [21] The first process is Penning ionization (Eq. 2.6), [22] the second is associative ionization which is also known as the Hombeck-Molnar process (Eq. 2.7). [23]... 

Penning ionization occurs with the (trace) gas M having an ionization energy lower than the energy of the metastable state of the excited (noble gas) atoms A. The above ionization processes have also been employed to construct mass spectrometer ion sources. [21,24] However, Penning ionization sources never escaped the realm of academic research to find widespread analytical application. 

Fig. 5.2. Processes under electron ionization conditions. Under certain conditions, Penning ionization could also play a role (Chap. 2.2.1.). Adapted from Ref. [8] with permission. Springer-Verlag Heidelberg, 1991.

Note The process M H- X -> MX" + e , i.e., ionization of internally excited molecules upon interaction with other neutrals is known as chemi-ionization. Chemi-ionization is different from Cl in that there is no ion-molecule reaction involved [8,15] (cf. Penning ionization. Chap. 2.2.1). 

In this chapter, firstly, a very brief survey is given of recent advances in such studies as classified according to the detection technique of transient species in pulse radiolysis. Secondly, examples are chosen from our recent investigations, with special emphasis on the important contributions of pulse radiolysis methods to gas-phase collision dynamics one is electron attachment, the other is Penning ionization and related processes. The detection techniques and corresponding reaction processes, together with major references, are given below ... 

De-excitation of excited rare gas atoms such as Penning ionization and related processes (see Section 3)... 

According to the theoretical investigations by Nakamura [126-128] and Miller [129], the collisional energy dependence of these processes can be calculated if the interaction potential V(R) for the system He(2 S)-M and the autoionization rate r K)jh from the intermediate quasi-molecule [He(2 S)M] to the resulting quasi-molecular ion [HeM] are known. For example, by the classical formula of Miller [129], we have theoretical cross sections for Penning ionization as ... 

A little more complicated system is the de-excitation of He(2 P) by Ne, where the deexcitation is dominated by the excitation transfer and only a minor contribution from the Penning ionization is involved. The experimental cross section obtained by the pulse radiolysis method, together with the numerical calculation for the coupled-channel radial Schrodinger equation, has clearly provided the major contribution of the following excitation transfer processes to the absolute de-excitation cross sections [151] (Fig. 15) ... 

Besides Penning ionization, electron tunneling is also registered in other autoionization phenomena in atomic collisions. For example, if the ionization energy of the A atom exceeds the sum of the first two ionization energies of the B atom, then a collision between the A+ ion and the B atom may involve an autoionization process [24]... 

Several books and review chapters devoted to the field of ion-neutral reactions in the gas phase have appeared in recent years, la 8, j,k some of which are concerned at least in part with the special topic of interest for the present review chapter—namely, the role of excited states in such interactions. The present review attempts to present a comprehensive survey of the latter subject, and the processes to be discussed include those in which an excited ion interacts with a ground-state neutral, interaction of an excited neutral with a ground-state ion, and on-neutral interactions that produce excited ionic products or excited neutral products. Reactions in which ions are produced by reaction of an excited neutral species with another neutral, for example, Penning ionization, are not included in the present chapter. For a recent review of this topic, the reader is referred to the article by Rundel and Stebbings.1 Electron-molecule interactions and photon-molecule interactions are discussed here only as they relate to the production of ions in excited states, which can then be reacted with neutral species. 

---