Ionization route

For microwave field stengths in the intermediate regime the quantum dynamics of the SSE system is still simple. It can be described in a multi-photon picture. For fixed microwave field strength we expect that the ionization probability exhibits a pronounced peak or threshold structure with large amounts of ionization occurring whenever the microwave frequency is in resonance with unperturbed SSE levels, or tuned to the ionization threshold. A schematic sketch of the first four SSE levels is shown in Fig. 6.7 together with possible ionization routes to the continuum. 

The data shown in Fig. 6.9 and Fig. 6.10 confirm our suspicion that for weak microwave fields no chaos mechanisms have to be invoked for an adequate physical understanding of microwave ionization data. The situation, however, is quite different in the case of strong microwave fields. In this case the ionization routes are very comphcated, and the multiphoton pictmre loses its attractiveness. It has to be replaced by a picture based on chaos. Chaos provides a simpler description of the ionization process and consequently a better physical insight. The discussion of the chaotic strong-field regime is the topic of the following section. 

According to the mechanisms outlined in Sections 1 and 2, substitution in the 3-position should preclude polymerization by the ionization route. This is indeed found to be so for example, sarcosine and proline NCAs ((IX), (X), respectively) cannot be polymerized by tertiary amines when... 

Characteristic for the fragmentation of the title compounds (237-243) are a very facile N—S bond cleavage (route A in equation 50 giving rise to 244) as in sulfonylhydrazides (Section V.C) and skeletal rearrangements accompanied by the extrusion of SO2 from the M and [M — 1] ions to the ionized JV-aryliminopyridinium betaines (245, compounds 237-239) or AT-imino-2-benzylpyridinium betaines (247, compounds 240-243 in equation 52) and azacarbazoles (246), respectively . Ion 244 decomposes further by elimination of HCN and via the loss of R N and HCN, as shown in equation (51). The sequence M " (240-243)- 247 ->248 (equation 52) is supported by the fact that AT-imino-a-alkylpyridinium betaines can lose an NH2 radical due to the operation of an ortho effect . 

The ionized atom that remains after the removal of the core hole electron is in a highly excited state and will rapidly relax back to a lower energy state by one of two routes, namely X-ray fluorescence (Section 5.1.2) or by transferring the energy to an electron in another orbit, which, if it has sufficient energy, will be ejected into the vacuum as Auger emission. An example of the latter process is illustrated in Figure 5.29. 

Routes C, D, and E. In these routes the C-3 ester function is cleaved under forms of RCOO% RCO-, and RCOOH, respectively. In the last case, ionized tropidine is formed. Concomitant losses of ethylene and hydrogen radical lead again to the /V-methylpyridinium ion (cf. Route A). 

At mucosal pH where drug is 100% ionized and Eq. (4) has accounted for pH partition shifts, nonzero permeability suggests that ionized drug (Kp close to zero) permeates the membrane by a route other than via lipid partition/diffusion. A discussion of such alternative pathways follows in Section m.C. 

A characteristic feature of ESMS is the detection of multiply charged analytes. Macromolecules, such as proteins have multiple sites where protonation or deprotonation (the two most common charge inducing mechanisms in electrospray—other routes to charge induction include, ionization through adduct formation, through gas-phase reactions, and through electrochemical oxidation or reduction) occur. These are desorbed effectively in ESMS and... 

Schneiter, R. Brugger, B. Sandhoff, R. Zellnig, G. Leber, A. Lampl, M. Athenstaedt, K. Hrastnik, C. Eder, S. Daum, G. Paltauf, F. Wieland, F. T. Kohlwein, S. D. Electrospray ionization tandem mass spectrometry (ESI-MS/MS) analysis of the lipid molecular species composition of yeast subcellular membranes reveals acyl chain-based sorting/remodeling of distinct molecular species en route to the plasma membrane. J. Cell Biol. 1999,146,741-754. 

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