Gas-phase ion chemistry

The mass spectrometer can be regarded as a kind of chemistry laboratory, especially designed to study ions in the gas phase. [1,2] In addition to the task it is usually employed for - creation of mass spectra for a generally analytical purpose - it allows for the examination of fragmentation pathways of selected ions, for the study of ion-neutral reactions and more. Understanding these fundamentals is prerequisite for the proper application of mass spectrometry with all technical facets available, and for the successful interpretation of mass spectra because Analytical chemistry is the application of physical chemistry to the real world. [3] 

In the first place, this chapter deals with the fundamentals of gas phase ion chemistry, i.e., with ionization, excitation, ion thermochemistry, ion lifetimes, and reaction rates of ion dissociation. The final sections are devoted to more practical aspects of gas phase ion chemistry such as the determination of ionization and appearance energies or of gas phase basicities and proton affinities. 

Brief discussions of some topics of this chapter may also be found in physical chemistry textbooks however, much better introductions are given in the specialized literature. [4-11] Detailed compound-specific fragmentation mechanisms, ion-molecule complexes, and more are dealt with later (Chap. 6.). 

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Dessent C E FI and Johnson M A 1998 Fundamentals of negative ion photoelectron spectroscopy Fundamentals and Applications of Gas Phase Ion Chemistry ed K R Jennings (Berlin Kluwer)... 

Mead R D, Stevens A E and Lineberger W C 1984 Photodetachment in negative ion beams Gas Phase Ion Chemistry ed M T Bowers (New York Academic)... 

Graul S T and Squires R R 1988 Advances in flow reactor techniques for the study of gas-phase ion chemistry Mass Spectrom. Rev. 7 263-358... 

Knighton W B and Grimsurd E P 1996 Gas phase ion ohemistry under oonditions of very high pressure Advances in Gas Phase Ion Chemistry ed N G Adams and L M Baboook (JAI)... 

Adams N G and Babcock L M (eds) 1992, 1996 and 1998 Advances in Gas Phase Ion Chemistry vols 1-3 (Greenwich, CT JAI) On ongoing series about current topics in ion chemistry. 

This is the seminal book on metastable ions, their chemistry and experimental observation. It is a must for anyone starting out in gas-phase ion chemistry. 

Blades A T, Jayaweera P, Ikonomou M G and Kebarle P 1990 Studies of alkaline earth and transition metal M " gas phase ion chemistry J. Chem. Phys. 92 5900... 

ITiscusaioa of (be techniques for gas-(>haau equilibrium meaauiuncaita can be found in T. A. Lehman and M. M. Buisey, Ion Cyclotron Resonance ectrometry, Wiky-Interscience, New yfaik, 1976 M. T. Bowers, ed., Gas Phase Ion Chemistry, Vols. I and 2, Aeadetnic Press, New Ypik, 1979. 

Schroder D, Schwarz H (2003) Diastereoselective Effects in Gas-Phase Ion Chemistry. 225 129-148... 

Schwarz, H. (2003) Relativistic Effects in Gas-Phase Ion Chemistry An Experimentalist s View. Angewandte Chemie International Edition, 42, 4442-4454. 

Shaik, S., Danovich, D., Fiedler, A., Schroder, D., Schwarz, H., 1995, Two-State Reactivity in Organometallic Gas-Phase Ion Chemistry , Helv. Chim. Act., 78, 1393. 

Advances in Gas-Phase Ion Chemistry Volume 3, pages 49-80 Copyright 1998 by JAI Press Inc. 

Gas-phase ion chemistry has applications in many areas however there are two fields to which the connection may be viewed as most important analytical mass... 

The first systematic measurements of the reactions of ions with molecules in the gas phase were initiated largely by workers associated with analytical mass spectrometry.4-6 It was the rapidly expanding area of ion-molecule reactions which led to the origin of Gas-Phase Ion Chemistry as a distinct field.7 The discovery that ion-molecule equilibria in the gas phase can be determined by mass spectrometric techniques8 led to an explosion of thermochemical measurements based on determination of equilibria by a variety of techniques.9 Significantly, for the first time, information could be obtained on the thermochemistry of reactions which had solution counterparts of paramount importance such as acidities and basicities. These were obtained from proton transfer equilibria such as,... 

We have discussed above some of the applications of gas-phase ion thermochemical data to ionic reactions in solution. However the new analytical ion-transfer from solution to the gas-phase techniques have also created an application for these data in the new analytical mass spectrometry. In fact, much of the background knowledge required for this new analytical mass spectrometry, and particularly MALDI and electrospray, is the gas-phase ion chemistry developed for applications... 

The thermochemical determinations involving ions obtained via ES, described in this work, provide an illustration of opportunities presented by the ES method. However, these are only the beginning of what we believe should become an important area in gas-phase ion chemistry. The ion equilibria measurements, so far performed in our laboratory, were restricted by the limited upper temperature (T < 500 K). This restriction was due to the cryopumping used and could be easily overcome and the temperature extended upwards by -200 K by using conventional pumping. 

The extension of analytical mass spectrometry from electron ionization (El) to chemical ionization (Cl) and then to the ion desorption (probably more correctly ion desolvation ) techniques terminating with ES, represents not only an increase of analytical capabilities, but also a broadening of the chemical horizon for the analytical mass spectrometrist. While Cl introduced the necessity for understanding ion—molecule reactions, such as proton transfer and acidities and basicities, the desolvation techniques bring the mass spectrometrist in touch with ions in solution, ion-ligand complexes, and intermediate states of ion solvation in the gas phase. Gas-phase ion chemistry can play a key role in this new interdisciplinary integration. 

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