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Infrared photophysics of gas phase ions in a Fourier transform ion cyclotron resonance mass spectrometer
| Title: | Infrared photophysics of gas phase ions in a Fourier transform ion cyclotron resonance mass spectrometer |
| Author: | Uechi, Guy Takeo |
| Description: | Infrared radiative cooling of vibrationally excited n-butylbenzene ions was studied in chapter III. This was done by a technique called ion thermometry, where the internal energy of the ions could be probed by the branching ratio of two competitive photoproducts. The infrared radiative cooling rate constant was observed to be 0.8 s-1 for ions with energies of only 0.3 eV above room temperature. Confidence in the thermometric data depended on the reliability of the measured branching ratios. In chapter IV a computer simulation was used to show that erroneous peak height ratios were produced by the Coulombic repulsion between ions during ion excitation, and reliable ratios could be obtained by working at low excitation, and reliable ratios could be obtained by working at low ion densities and using a short excitation pulse. Chapter V discussed our first attempt to describe infrared multiphoton dissociation (IRMPD) of trapped ions in a thermal framework. Using a computer simulation the laser intensity was associated with an internal ion temperature for ions undergoing continuous laser irradiation. An Arrhenius type plot was constructed, and the activation energy obtained from it seemed reasonable within the expectations from Tolman’s theorem. To pursue the feasibility of the thermal analysis of IRMPD kinetics, the thermometric technique was used in chapter VI to observe the CO2 laser pumping process for n-butylbenzene ions. The data showed that the steady state distribution of the ion energies reached during laser pumping is very dependent on the rate of photon absorption and emission. The generalized thermal analysis which was done in chapter V was found to be unfeasible. Ion thermometry was also used in chapter V to observe the rate of photon emission from n-butylbenzene ions heated by the cw-CO2 laser. Although the ions contained 0.3 eV more energy than the ions studied in chapter 2, the observed rate of cooling was the same. Chapter VII describes the association reactions between silicon ions and a series of aromatic molecules (benzene, naphthalene, and anthracene). These reactions are mediated by the emission of an infrared photon, thereby termed radiative association reactions. In all three cases the silicon ion inserted into the C-H bond of the molecules as shown by the collision induced dissociation spectra of the association product ions. |
| Permanent Link: |
http://rave.ohiolink.edu/etdc/view?acc_num=case1056650065
http://hdl.handle.net/2374.OX/103963 |
| Date: | 1993 |
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