Two gas-phase ion-molecule reaction systems are presented here based on
measurements done in a temperature variable 22-pole trapping machine. In the first case, the proton affinity of methane is determined based on a new technique for measuring the equilibrium constant of the HCO2+ + CH4 <=>
CH5+ + CO2 reaction. The second case reports to the (Ar + N2 )+ reaction system, with reaction rate temperature dependencies measurements made both in the forward and reverse direction with different and complementary methods. The temperature variable 22-pole trapping machine allows one to determine equilibrium constants and reaction rate coefficients over a wide range of temperatures. The coupling of an effusive beam to the setup overcomes the problem of neutral gas wall condensation and extends the temperature range measurements beyond condensation point. The introduction (Chapter 1) gives a short overview about the rf technology and parallel experimental techniques developed in order to better characterize and understand the several mechanisms related to ion-molecule reactions. It also focuses some aspects of reaction rate temperature dependencies determination as well as thermodynamical equilibrium in laboratory environment. A short description of the setup and experimental methods are presented in Chapter 2. Based on equilibrium constant measurements, Chapter 3 is dedicated to the proton affinity of methane. This concept has applications on several fields such as atmospheric and combustion modelling, or testing empirical and ab initio theories for electronic structures. The (Ar − N2 )+ system presented in Chapter 4, is known for being a good case study for inferring the role of vibrational excitation in reaction dynamics and to the existence of non-adiabatic coupling. The experimental results here presented for the N2+ + Ar reaction demonstrate that it is possible to avoid parallel reactions with first vibrational excited state of nitrogen (N2 (ν = 1)). On the other hand, the reverse reaction experiments confirm the existence of a minimum of the reaction rate in the 30 to 300 K range, due to the existence of two reaction channels. The question of the high rate coefficient towards lower temperatures being related to the N2 rotational ground state population is raised. A summary and outlook are presented in Chapter 5, where some new possible paths of investigation are pointed out.
| Identifer | oai:union.ndltd.org:DRESDEN/oai:qucosa:de:qucosa:19413 |
| Date | 27 October 2010 |
| Creators | Mogo, César |
| Contributors | Gerlich, Dieter, Magerle, Robert, Technische Universität Chemnitz |
| Source Sets | Hochschulschriftenserver (HSSS) der SLUB Dresden |
| Language | English |
| Detected Language | English |
| Type | doc-type:doctoralThesis, info:eu-repo/semantics/doctoralThesis, doc-type:Text |
| Rights | info:eu-repo/semantics/openAccess |
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