Polyatomic ions, 49 atmospheric

Figure 7.13 presents a vertical distribution of and N0+ as observed by Keneshea et al. (1970). Figure 7.14 presents a schematic diagram of E-region ion chemistry. For completeness, it should be noted that the 0+ produced by photoionization is destroyed rapidly by reaction with 02, N2, and C02, and thus plays a negligible role in the middle atmosphere. Its maximum density reaches only about 10 percent of that of C>2. All of these polyatomic ions are produced directly by ionization or charge transfer with neutral species, and are referred to as molecular ions. 

In this section, the approach of Mason and McDanieP and their colleagues has been adopted, and emphasis is given to analysis of the motion of relatively large polyatomic ions in a buffer gas at atmospheric pressure in a weak electric field. 

Polyatomic Ion Interferences. An interference problem that is usually more serious than that caused by iso-baric elements occurs when polyatomic species form from interactions between species in the plasma and species in the matrix or the atmosphere. These species may then produce several molecular ions that interfere. This type of interference is found usually at m/z values of below about 82. The presence of several of these species is shown in bigure Il-I5b. Among the potential interferentsarc Ar", ArH, " O,. " OH ,... 

Nevertheless, let us remember that Debye and Hiickel s law supposes the ions are spherical, which can be accepted for sufficiently dilute solutions in which the radius of the ionic atmosphere is larger than a and therefore in which the ions are relatively far removed from one another. If the ions come closer together, the hypothesis of sphericity becomes trickier to accept for a large number of t5q)es of ions - particularly for polyatomic ions. 

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