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Title
Spectroscopic Studies of a Triatomic Molecular Anion
Additional Titles
Spectroscopic Studies of a Triatomic Molecular Anion
AuthorLakhmanskaya, Olga
Thesis advisorWester, Roland
Published2018
Institutional NoteInnsbruck, Univ., Diss., 2018
Date of SubmissionJuly 2018
LanguageEnglish
Document typeDissertation (PhD)
Keywords (DE)asymmetric top / NH2- / NH2 / photodetachment spectroscopy / rotational spectroscopy / inelastic collision rate / ortho to para ratio / 22-pole radiofrequency ion trap / radiofrequency heating / ion temperature
Keywords (EN)asymmetric top / NH2- / NH2 / photodetachment spectroscopy / rotational spectroscopy / inelastic collision rate / ortho to para ratio / 22-pole radiofrequency ion trap / radiofrequency heating / ion temperature
URNurn:nbn:at:at-ubi:1-30038 Persistent Identifier (URN)
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 The work is publicly available
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Abstract (German)

Molecular spectroscopy is involved in the studies of fundamental physical and chemical processes as well as in technical applications. 22-pole radio frequency ion traps provide a suitable environment for these studies. Their large almost field free region allows efficient translational and internal cooling of different molecules by buffer gas. In the first part of this thesis we analyze loss mechanisms of ions in these traps. Experimental data shows good agreement with our simulations and will be useful for planning future experiments and new trap designs.

The main part of the thesis focuses on spectroscopic studies of NH2-. The molecule is particularly interesting for astronomers [Persson2014] and has a direct relation to the nitrogen chemical network. Furthermore, the molecule belongs to the class of asymmetric top molecules and appears in two nuclear spin forms, ortho and para, which is very interesting from a fundamental point of few.

Until recently, NH2- lacked high resolution spectroscopic data. The only available rotational constants were known from infrared spectroscopy [Tack1986] and contain significant uncertainties on the order of 100 MHz, thus prohibiting the prediction of high resolution rotational spectra. One of the most important characteristics of negative ions the binding energy of the excess electron (the electron affinity of NH2 ) was known with an uncertainty of 40 cm1 for NH2-. This uncertainty was reduced in this work by photodetachment

spectroscopy near threshold. The analysis of the spectra allowed an assignment of the electron affinity of NH2 with a 40 fold improvement in accuracy. We have also measured the rotational temperature of the anions. Good agreement with the theoretically predicted exponent factors for the Wigner threshold law was observed.

Furthermore, photodetachment was used in experiments on rotational transitions of NH2 and in the study of the ortho to para dynamics. We successfully detected the two fundamental rotational transitions for ortho and para NH2 which should facilitate the identification of this molecule in space and thus the development of astrochemical models. We also demonstrated how the ortho to para ratio of NH2- in the trap can be manipulated with the photodetachment laser. The results were analyzed with the aid of the quantum chemical inelastic collisional rate studies performed by the theoreticians in our group. The results are especially interesting for further experiments such as the inelastic rate measurements and determination of the reaction rates of ortho and para species in the reaction NH2- + H2 NH3 + H-.

Abstract (English)

Molecular spectroscopy is involved in the studies of fundamental physical and chemical processes as well as in technical applications. 22-pole radio frequency ion traps provide a suitable environment for these studies. Their large almost field free region allows efficient translational and internal cooling of different molecules by buffer gas. In the first part of this thesis we analyze loss mechanisms of ions in these traps. Experimental data shows good agreement with our simulations and will be useful for planning future experiments and new trap designs.

The main part of the thesis focuses on spectroscopic studies of NH2-. The molecule is particularly interesting for astronomers [Persson2014] and has a direct relation to the nitrogen chemical network. Furthermore, the molecule belongs to the class of asymmetric top molecules and appears in two nuclear spin forms, ortho and para, which is very interesting from a fundamental point of few.

Until recently, NH2- lacked high resolution spectroscopic data. The only available rotational constants were known from infrared spectroscopy [Tack1986] and contain significant uncertainties on the order of 100 MHz, thus prohibiting the prediction of high resolution rotational spectra. One of the most important characteristics of negative ions the binding energy of the excess electron (the electron affinity of NH2 ) was known with an uncertainty of 40 cm1 for NH2-. This uncertainty was reduced in this work by photodetachment

spectroscopy near threshold. The analysis of the spectra allowed an assignment of the electron affinity of NH2 with a 40 fold improvement in accuracy. We have also measured the rotational temperature of the anions. Good agreement with the theoretically predicted exponent factors for the Wigner threshold law was observed.

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