Flowing afterglow ion source

Fig. 6. A flowing afterglow ion source used by Milligan et al. [42] in the study of the HJ+N reaction. Ions are generated by electron impact, or by the action of a microwave discharge...

The electronic structure and gas-phase thermolysis of 4-substituted 3,3,5,5-tetramethyl-3,5-dihydro-4//-pyrazoles has been studied by photoelectron spectroscopy and the first evidence for an alkylideneselenirane was obtained <1996T1965>. The 351.1 nm photoelectron spectrum of the 1-pyrazolide anion has been measured <2006PCA8457>. The 1-pyrazolide ion 29 is produced by hydroxide deprotonation of pyrazole in a flowing afterglow ion source and a small amount of the 5-pyrazolide ion 30 was also detected and studied by photoelectron spectroscopy. 

The elusive o-, m- and -benzynes (23-25) can be prepared in the gas phase by CAD of 0-, m- and / -chlorophenyl anions, respectively (Scheme 17) ". These anions are readily accessible in a flowing afterglow ion source by appropriate ion-molecule reactions The o-anion (23a ) is formed in isomerically pure form by proton abstraction from chlorobenzene by furanide anion the m- and -anions (24a , 25a") are generated from the reactions between F" and the corresponding (chlorophenyl)trimethylsilanes (Scheme 17). 

Jecklin, M.C., Schmid, S Urban, P.L., Amantonico, A., Zenobi, R. (2010) Miniature Flowing Atmospheric-pressure Afterglow Ion Source for Facile Interfacing of CE with MS. Electrophoresis 31 3597-3605. 

Most of the studies in this decade were carried out with conventional single source mass spectrometers, which limited the kind and accuracy of the information. During the next decade, however, various sophisticated techniques for the study of ion—molecule reactions, such as tandem mass spectrometers, photoionization sources, pulsed sources, flowing afterglow and drift tube methods, crossed and merging beams and ion cyclotron resonance, have been developed. Much detailed information on various aspects of ion—molecule reactions has accumulated, and this has consequently stimulated the theoretical studies as well. This decade was, so to speak, the second epoch in the history of ion—molecule studies. 

Electron attachment ionization should also be mentioned here. In this case, the goal is to deposit an electron on the neutral Y to produce the anion Y . When compounds have appreciable electron affinity, this can be accomplished easily by using an electron beam set at a very low potential (a few volts), allowing electron capture by the neutral molecule in the source. The flowing afterglow method can be applied to study the dynamics for organometallic ion-molecule reactions, particularly for anions. 

In other studies of reaction (29), Curran reported that charge transfer occurred in an ion source experiment with Cl formed by dissociative attachment in CCI4 and concluded that A(N02) EA(C ) = 3.613 eV. However, Ferguson et a/. - were unable to observe reaction (29) in the flowing afterglow with A" = Cl and F. 

MS Mass spectrometer ion source. LP Low pressure <10 pim. MP Medium pressure <100 /im. ICR Ion cyclotron resonance. FAG Flowing afterglow. 

A schematic of a typical version of the NOAA flowing afterglow system is shown in Fig. 1. In brief, a large flow of buffer gas (180 atm cm sec" ), usually helium, is introduced into the front end of a stainless steel tube approximately 8 cm in diameter, down which it is exhausted by a large pump, typically at 10" cm sec" and with 0.3 Torr pressure. A suitable source gas to produce the desired reactant ions is added either with the helium or downstream of the helium addition as shown in Fig. 1. The helium (and the source ion gas if it is added ahead of the electron gun) are ionized by an electron beam of variable voltage and current in such a fashion as to produce the desired reactant ion in the flowing stream before arrival at the neutral reactant addition port. The ion composition is... 

The flowing afterglow (FA) is a flow reactor tube. Ions are produced by an ion source at the upstream end of the tube. These ions are carried by a buffer gas (He or Ar) and thermahzed to room temperature down the flow tube. On their way down, they react with neutral molecules added downstream in the tube. The (ionic) reaction products can be moiutored in a number of ways, including optical spectroscopy and MS. In the latter case, the resulting swarm of ions is sampled through an orifice into a high-vacuum chamber where they are mass analyzed and detected. 

Fig. 4.7 Schematic diagram of a flowing afterglow mass spectrometry setup. The system is setup to perform reactions with H3O+. Other primary ions can be generated by other types of ion sources. (Adapted from ref [121] and Smith, D. panel, R Selected ion flow tube mass spectrometry (SlFT-MS) for online trace gas analysis. Mass Spectrom Rev. 24, 2005, 661-700] with permission of Wiley. 2001 and 2005, Wiley, Ltd.)...

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