Highly ionized spectra

Quite often a normal electron ionization mass spectrum appears insufficient for reliable analyte identification. In this case additional mass spectral possibilities may be engaged. For example, the absence of the molecular ion peak in the electron ionization spectrum may require recording another type of mass spectrum of this analyte by means of soft ionization (chemical ionization, field ionization). The problem of impurities interfering with the spectra recorded via a direct inlet system may be resolved using GC/MS techniques. The value of high resolution mass spectrometry is obvious as the information on the elemental composition of the molecular and fragment ions is of primary importance. 

Note If a peak is not present in the low-resolution mass spectrum, there is no reason why it should be detectable from the high-resolution spectrum as long as the same ionization method is employed. Instead, use of a more suitable ionization method is recommended. (And sometimes one has to accept the truth that the sample is not what it was expected to be.)... 

The field decreases less rapidly than n 4 because of the increasing number of high m states with increasing n. This method allows a unique transformation from the field ionization spectrum to an n distribution. 

Figure 1 X-ray emission spectrum of highly ionized neon plasma. Reused with permission from [93] 1992, American Institute of Physics...

This system forms highly ionized so-called Penning mixtures [12,13]. The higher excited states of Hj are partly stable and partly unstable, depending on the quantum numbers of the electron present. The stable excited states have, however, only very shallow minima of the potential curves [14]. That is the reason why no spectrum of Hj is observed for the helium plasma jet. The argon excited neutrals, on the other hand, cannot ionize hydrogen atoms or molecules, but could produce excited H2 molecules, which can be detected by optical emission spectroscopy. 

In Figure 18-lc, the formation of cyclic trimeric silicic acid (0 3) is observed. Probably due to the high ionization of silicic acid species in the aqueous silicate solution, oligomerization of the d eric silicic acid proceeds via the cyclic trimeric isomer of trimeric silicic acid. In a later stage of the dissolution process, the formation of the linear isomer of trimeric silicic acid is encountered in the silicon-29 nmr spectrum (Figure 18-Id). Preferential formation of cyclic trimeric sUicic acid is attributed to charge stabilization of the trimeric species. Ab initio quantum mechanic calculations of cyclic structures of silicate units (Van Beest, Verbeek, and Van Santen... 

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