Mehrphotonen-Ionisationsspektroskopie von Ammoniak und Methylamin

In der vorliegenden Arbeit wurden die C'-Rydbergzustände der Ammoniakisotopomere und des Methylamins mit Hilfe der resonanzverstärkten Mehrphotonenionisation untersucht. Es wurde für die REMPI-Spektren aller Ammoniakisotopomere (NH3, NH2D, NHD2 und ND3) des C'-Zustandes mit v = 0, 1 eine...

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Bibliographic Details
Main Author: Nolde, Moana
Contributors: Weitzel, Karl-Michael (Prof. Dr.) (Thesis advisor)
Format: Dissertation
Published: Philipps-Universität Marburg 2006
Online Access:PDF Full Text
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Table of Contents: In this work the C'-Rydbergstates of ammoniaisotopomers and methylamine were examined by resonance enhanced multiphoton ionization. The REMPI-spectra of all ammoniaisotopomers (NH3, NH2D, NHD2 and ND3) in the C'- state with v = 0, 1 were studied in great detail and the spectroscopic parameters, i. e. rotational constants, centrifugal distortion constants and the origins of the spectra, were determined. The spectra in both vibrational states of the symmetric isotopomers are rotationally well-resolved. Therefore it is possible to assign the rotational transitions by comparison of the experimental data with simulated spectra. The derived spectroscopical constants were compared with previously published results. Since no spectrosopical constants of the partially deuterated isotopomers are known so far, this work presents the first thorough spectral analysis of NH2D and NHD2 in the C'- state. The spectra in C'- state with v = 0 of the asymmetric isotopomers are also rotationally well-resolved, whereas those with v = 1 show significant line broadening due to predissociation. For the simulation of these spectra the predissociation was taken into account. All spectra show protruding peaks in the progression of the Q-branch with K = J and K = 0 for the symmetric and Kc = J, Ka = J for the asymmetric isotopomers. These transisions can be assigned accurately and offer the opportunity to manipulate the rotational state in state selected ions. The rotational constants can be classified with respect to the isotopomer or the vibrational state. Within a vibrational state all rotational constant decrase with increasing mass of the isotopomere. On the other hand the constants A and B increase while C decreases with increasing vibrational quantum number for every isotopomer. Apart from the ammoniaisotopomers the REMPI-spectra of the ammonia derivative methylamine were investigated. The time-of-flight-massspectrum of methylamine shows a characteristic fragmentation pattern. In this thesis a possible reaction mechanism for the decay is proposed and compared with the order of the excitationprocess. A rate constant (k > 10^8 s^-1) for the decay was evaluated. Furthermore the spectra in the region of 57000-67000 cm^-1 were analysed with respect to the NH2-wagging and CH3-rocking modes. The vibrational frequencies were determined as (730 ± 10) cm^-1 and (1000 ± 10) cm^-1 respectively. So far no experimental data has been published for this region of methylamine. By comparison with VUV-publications the investigated absorption band has been assigned to a C'-state of the methylamine.