Synchrotron radiation induced fluorescence spectroscopy of gas phase molecules

by Álvarez Ruiz, Jesús

Abstract (Summary)
A new experimental set-up for gas phase fluorescence studies using synchrotron radiation has been designed and constructed to perform simultaneously total and dispersed fluorescence measurements. Neutral photodissociation of CO has been investigated after excitation with 19-26 eV photons. Fluorescence from 3p 3P, 3p 3S and 3p 1D excited states in carbon was recorded and interpreted by ab initio calculations. The population and dissociation of states belonging to the C and D Rydberg series in CO seem to explain the production of the observed triplet states but not the 3p 1D state. Neutral photodissociation of NO is reported in the 17-26 eV energy range. No known molecular states can account for the collected data. New information regarding the precursor states of the observed neutral dissociation is provided by ab initio calculations. Autoionization of superexcited states in molecular nitrogen is evidenced by strong deviations of the Franck-Condon ratio in the fluorescence of the N2+ B state. Ab initio calculations predict the existence of autoionizing-excited states that may account for some of the observed structures in the 20-46 eV energy range. Selective molecular fluorescence from the npó1Óu+ and npð 1Ðu (n=3-7) Rydberg levels to the E,F 1Óg+ state in H2 was recorded and rotationally analyzed. Vibrational levels of the E,F 1Óg+ state (vEF =0,1,3,6-10) are determined. The predissociation of npð 1Ð+ levels is observed in agreement with the literature. Fragmentation of SF6 was investigated after excitation with 25–80 eV photons. Dispersed fluorescence measurements reveal the emission of S, S+, F and F+ excited atoms. These fragments are produced after single, double and triple excitations as well as direct ionizations and shake-ups in SF6. Photoabsorption and fluorescence yield have been measured in SF5CF3 using 10-30eV photons. The photoabsorption spectrum can be explained in terms of its similarities to those of the SF6 and CF4 molecules. The dispersed and un-dispersed fluorescence resemble those of the CF3X family. Several features suggest the migration of an F atom across the S-C bond that fragments the molecule producing excited CF4. Doubly excited states of H2 have been investigated in the range of 26-60 eV by monitoring Balmer á emission. The experimental data show the already known emission correlated with the fragmentation of the Q1 and Q2 states, and new features which could be attributed to dissociative photoionization and higher lying doubly excited states Qn (n>2) of the hydrogen molecule
Bibliographical Information:


School:Kungliga Tekniska högskolan

School Location:Sweden

Source Type:Doctoral Dissertation

Keywords:NATURAL SCIENCES; Physics; Physics; molecular spectroscopy; photon induced fluorescence; synchrotron radiation; superexcited states; Fysik


Date of Publication:01/01/2004

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