Reionization

Figure Bl.7.7. Summary of the other collision based experiments possible with magnetic sector instruments (a) collision-mduced dissociation ionization (CIDI) records the CID mass spectrum of the neutral fragments accompanying imimolecular dissociation (b) charge stripping (CS) of the incident ion beam can be observed (c) charge reversal (CR) requires the ESA polarity to be opposite that of the magnet (d) neutiiralization-reionization (NR) probes the stability of transient neutrals fonned when ions are neutralized by collisions in the first collision cell. Neutrals surviving to be collisionally reionized in the second cell are recorded as recovery ions in the NR mass spectrum.

Sulfurous acid has never been isolated as a pure compound, although it has recently been detected in the gas phase by neutralization reionization mass spectrometry (NRMS) following the facile dissociative ionization (70 eV) of either diethyl sulfite or ethanesulfonic acid " ... 

The oxide S3O has been identified only in the gas-phase by means of neutralization reionization mass spectrometry [58]. The precursor ion SsO was generated by the following sequence of reactions ... 

The SsO ion was then mass selected and neutralized by electron exchange with Xe atoms. The neutral beam was reionized by collision with O2 and the... 

Turecek F (2003) Transient Intermediates of Chemical Reactions by Neutralization-Reionization Mass Spectrometry. 225 75-127... 

Turecek F (2003) Transient Intermediates of Chemical Reactions by Neutralization-Reionization Mass Spectrometry. 225 75-127 Ublacker GA.see Maul JJ (1999) 206 79-105 Uemura S,see Nishibayashi Y (2000) 208 201-233 Uemura S, see Nishibayashi Y (2000) 208 235-255... 

Based on the ACDM concordance cosmological model and adopting the maximum circular velocity as the rotational velocity at the last measured point, we have obtained the DM mass of the galaxy (3.4 x 1010Mq). We use the recipe for the halo mass assembly history described by van den Bosch (2002) and the effect that reionization has on the infalling gas (Kravtsov et al., 2004) to derive the rate at which gas is accreted by the galaxy. 

The major fragmentation in mass spectra of 1,2,5-oxadiazoles is attributed to the loss of nitrile and nitrile oxide or expulsion of NO. The conversion of 3,4-dicyano-l,2,5-oxadiazole-2-oxide (3,4-dicyanofuroxan) 10 to cyanogen iV-oxide 11 (Equation 5) was investigated under the conditions of collisional activation (CA) and neutralization-reionization (NR) mass spectrometry. Flash vacuum thermolysis mass-spectrometry (FVT-MS) and flash vacuum thermolysis infra-red (FVT-IR) investigations of furoxans 10, 12, and 13 reveal that small amounts of cyano isocyanate accompany the formation of the main thermolysis product 11 <2000J(P2)473>. 

C-Acyl nitroso compounds are highly reactive species and no examples of stable and isolable C-acyl nitroso compounds have been reported. Charge-reversal and neutraHzation-reionization mass spectrometry experiments provided the first spectroscopic evidence for the existence of acyl nitroso compounds in the gas phase [30,... 

In this chapter we describe briefly the physical phenomena, such as sputtering, scattering, neutralization and reionization, that are involved in ion spectroscopy. For a detailed description of the interactions of ions with solids we refer to the books by Feldman and Mayer [1], Benninghoven, Riidenauer and Werner [2], and Czandema and Hercules [3]. 

The incident ion is neutralized inside the solid. For example, IkeV He+ ions have a neutralization probability of about 99% in passing through one layer of substrate atoms. Hence, the majority of ions that reach the detector must have scattered off the outermost layer (or were reionized upon leaving the solid, as we will see further on). 

Thus in order to understand ion scattering with low energy ions, we need to understand not only the scattering process but also the probabilities of neutralization and reionization. 

A second type of neutralization occurs through a resonance process, in which an electron from the sample tunnels to the empty state of the ion, which should then be at about the same energy. Resonance neutralization becomes likely if the electron affinity of the ion is somewhat larger than the work function of the sample, or if the ion has an unfilled core level with approximately the same energy as an occupied level in the target atom. The latter takes place when He+ ions come near indium, lead or bismuth atoms. The inverse process can lead to reionization. 

Neutralization-reionization mass spectrometry (NRMS) is used to generate neutral species in the gas phase that are difficult to prepare or identify by other methods. During NRMS, both cations and anions may be neutralized, generally by collision, and then reionized to confirm the stability of the neutral species. Two reviews, with particular examples in coordination chemistry, provide good information on this method and offer many examples (76,77). A good example is AuF, which has been predicted to be stable. The [AuF]+ and AuF complexes were both neutralized and reionized and the AuF species was obtained in each recovery signal. It was postulated that the elusiveness of this molecule in the condensed phases was not due to instability but rather to inter-molecular reactions (78). 

Although no En cluster molecules with n > 4 are known in the condensed phase, it has been shown [27] that neutral P6 can be generated in the gas phase by neutralization-reionization mass spectrometry with cp 2 6 as a precursor [cp = C5(CH3)5] [28]. Since the cp 2P6 precursor molecule already has a hetero-benzvalene P6 skeleton, it was inferred that the neutral P6 molecule should have the benzvalene structure as shown in Figure 2.6-5. This is in agreement with a multitude of quantum chemical calculations [8, 11, 27, 29-32]. Note that the handle of the basket of P6 includes two dicoordinate P atoms linked by a P=P double bond (cf. R-P=P-R 203 pm [33]). 

During the last decade knowledge of the ion chemistry of nitro compounds in the gas phase has increased significantly, partly due to the more widespread use of specialized techniques. Thus various ionization methods, in particular electron impact ionization and chemical ionization, have been used extensively. In addition, structure investigations as well as studies on fragmentation pathways have involved metastable ion dissociations, collision activation and neutralization/reionization studies, supplementary to studies carried out in order to disclose the associated reaction energetics and reaction dynamics. In general, the application of stable isotopes plays a crucial role in the in-depth elucidation of the reaction mechanisms. 

The technique of neutralization/reionization mass spectrometry (NRMS), originally introduced by McLafferty, invokes the formation of fast neutrals from a preselected ion beam, any residual ions being deflected, followed by collision-induced reionization of the neutrals and a subsequent mass spectrometric analysis16-21. 

FIGURE 4. Neutralization/reionization mass spectrum of [M — C2H4]+ ion of 1-nitropropane15... 

The sites of protonation of aromatic compounds, including the possible three mono fluoronitrobenzenes, have been studied by neutralization-reionization mass spectrometry (NRMS)22. The NRMS experiments on the MD+ species generated by D2 chemical ionization clearly indicated that the D+ attachment takes place to the nitro group rather than to the aromatic ring, as evidenced by the abundant losses of OD and DNO2 (NO + OD )22. 

Schwarz and coworkers115 used 1,2,3-butatriene, along with 1,3-butadiyne, as a precursor for the generation of neutral 1,2,3-butatrienylidene in a neutralization/reionization mass spectrometric sequence (C4H4 - C4H2- - C4H2 - C4H2+ ). 

CH4/O2 and CF4 as the reactant gases and observed the formation of [M — 4 H] ions in the Cl plasma (Scheme 13)166. Thus, repeated deprotonation and electron transfer processes appear to offer an efficient access to more highly unsaturated and/or ring condensed trimethylenemethane radical anions. The [M — 4 H]- ion is considered identical to the molecular radical anion (42) of acepentalene (43), which was generated as a short-lived species from the former by neutralization-reionization mass spectrometry167. Efforts to apply Squires methodology to triquinacene 41 and the tribenzotriquinacenes 44 have been made168. 

Yates, B.F. Bouma, W.J. Radom, L. Detection of the Prototype Phosphonium (CH2PH3), Sulfonium (CH2SH2), and Chloronium (CH2CIH) Ylides by Neutralization-Reionization Mass Spectrometry a Theoretical Prediction. J. Am. Chem. Soc. 1984,106, 5805-5808. 

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