Chemical Sciences: A Manual for CSIR-UGC National Eligibility Test for Lectureship and JRF/Gas phase ion chemistry

Gas phase ion chemistry is a field of science encompassed within both chemistry and physics. It is the science that studies ions and molecules in the gas phase, most often enabled by some form of mass spectrometry. By far the most important applications for this science is in studying the thermodynamics and kinetics of reactions. Aubry C. 2000 Correlating thermochemical data for gas-phase ion chemistry International Journal of Mass Spectrometry 200 277 10.1016/S1387-3806(00)00323-7 Pure & Appl. Chem., Vol. 70, No. 10, pp. 1969-1976, 1998. For example one application is in studying the thermodynamics of the solvation of ions. Ions with small solvation spheres of 1, 2, 3... solvent molecules can be studied in the gas phase and then extrapolated to bulk solution. Theory Transition state theory Transition state theory Transition state theory is the theory of the rates of elementary reactions which assumes a special type of chemical equilibrium (quasi-equilibrium) between reactants and activated complexes.Transition State Theory T06470 RRKM theory RRKM theory RRKM theory is used to compute simple estimates of the unimolecular ion decomposition reaction rates from a few characteristics of the potential energy surface. Gas phase ion formation The process of converting an atom or molecule into an ion by adding or removing charged particles such as electrons or other ions can occur in the gas phase. These processes are an important component of gas phase ion chemistry. Associative ionization Associative ionization Associative ionization is a gas phase reaction in which two atoms or molecules interact to form a single product ion.associative ionization A00475 where species A with excess internal energy (indicated by the asterisk) interacts with B to form the ion AB+. One or both of the interacting species may have excess internal energy. Charge-exchange ionization Charge-exchange ionization Charge-exchange ionization (also called charge-transfer ionization) is a gas phase reaction between an ion and a neutral species in which the charge of the ion is transferred to the neutral.charge-exchange ionization C00989 Chemical ionization chemical ionization In chemical ionization, ions are produced through the reaction of ions of a reagent gas with other species.Munson, M.S.B.; Field, F.H. J. Am. Chem. Soc. 1966, 88, 2621-2630. Chemical Ionization Mass Spectrometry. I. General Introduction. Some common reagent gases include: methane, ammonia, and isobutane. Chemi-ionization Chemi-ionization Chemi-ionization can be represented by where G is the excited state species (indicated by the superscripted asterisk), and M is the species that is ionized by the loss of an electron to form the radical cation (indicated by the superscripted "plus-dot"). Penning ionization Penning ionization Penning ionization refers to the interaction between a gas-phase excited-state atom or molecule G* and a target molecule M resulting in the formation of a radical molecular cation M+., an electron e−, and a neutral gas molecule G:Penning gas mixture P04476 Penning ionization occurs when the target molecule has an ionization potential lower than the internal energy of the excited-state atom or molecule. Associative Penning ionization can also occur: Fragmentation There are many important dissociation reactions that take place in the gas phase. Collision-induced dissociation Collision-induced dissociation CID (also called collisionally activated dissociation - CAD) is a method used to fragment molecular ions in the gas phase.Wells JM, McLuckey SA Collision-induced dissociation (CID) of peptides and proteins Meth. Enzymol. 402 148–85 2005 16401509 10.1016/S0076-6879(05)02005-7Sleno L, Volmer DA Ion activation methods for tandem mass spectrometry Journal of mass spectrometry : JMS 39 10 1091–112 2004 15481084 10.1002/jms.703 The molecular ions collide with neutral gas molecules such as helium, nitrogen or argon. In the collision some of the kinetic energy is converted into internal energy which results in fragmentation. Charge remote fragmentation Charge remote fragmentation Charge remote fragmentation is a type of covalent bond breaking that occurs in a gas phase ion in which the cleaved bond is not adjacent to the location of the charge.Cheng C, Gross ML Applications and mechanisms of charge-remote fragmentation Mass Spectrom Rev 19 6 398–420 2000 11199379 10.1002/1098-2787(2000)19:6<398::AID-MAS3>3.0.CO;2-B Gross M. 2000 Charge-remote fragmentation: an account of research on mechanisms and applications International Journal of Mass Spectrometry 200 611 10.1016/S1387-3806(00)00372-9 Charge transfer reactions There are several types of charge-transfer reactionscharge-transfer reaction (in mass spectrometry) C01005 (also known as charge-permutation reactionscharge-permutation reaction M04002): partial-charge transfer , charge-stripping reactioncharge-stripping reaction C01001 , and charge-inversion reactioncharge-inversion mass spectrum C00992 positive to negative and negative to positive . References Bibliography Fundamentals of gas phase ion chemistry, Keith R. Jennings (ed.), Dordrecht, Boston, Kluwer Academic, 1991, pp. 226-8 Gas Phase Ion Chemistry, Michael T. Bowers, ed., Academic Press, New York, 1979 Gas Phase Ion Chemistry Vol 2.; Bowers, M.T., Ed.; Academic Press: New York, 1979 Gas Phase Ion Chemistry Vol 3., Michael T. Bowers, ed., Academic Press, New York, 1983