Synchrotron radiation; V-UV Photoabsorption; Vibrational excitation; Rydberg series; Jahn-Teller distortion; Ab initio calculations; Isotope effect; CH3Cl; CD3Cl
Abstract :
[en] The fine structure of the vacuum UV photoabsorption spectrum of CH3Cl and CD3Cl has been analyzed in the 7.5-10.5 eV photon energy range. A large number of lines have been observed, classified and assigned to vibrational excitation accompanying a series of Rydberg transitions. The vibronic transitions involve both Jahn-Teller distortion and spin-orbit splitting. The former effect has been evaluated by ab initio calculations showing that the 2E state (in the C3v symmetry group) splits into 2A' and 2A" states in the Cs symmetry group. The 2A' state is energetically the lowest component whereas the 2A" is found to be a transition state. The Jahn-Teller stabilisation energy and the wavenumbers associated with all vibrational modes have been calculated. Experimentally, the entire fine structure could be described by using the vibrational modes, i.e. hcomega5= 104+/-7 meV, hcomega6= 77+/-7 meV and homega=162+/-3 meV respectively, as resulting from an average over all the analyzed Rydberg states. In CD3Cl the corresponding energies are hcomega5= 81+/-4 meV, hcomega6= 66+/-5 meV and hcomega= 124+/-4 meV. These values are in good agreement with those predicted by the present ab initio calculations for the ion ground state. However, the agreement is not so good for the wavenumber omega which could be assigned to the nu3 or nu4 vibrational modes. Though some arguments favour nu4 (the CH3 umbrella mode), within the error limits on the present measurements it is formally not possible to ascribe this wavenumber to one of these two vibrations.
Research center :
Laboratoire de Dynamique Moléculaire, BESSY
Disciplines :
Chemistry
Author, co-author :
Locht, Robert ; Université de Liège - ULiège > Département de Chimie (Faculté des sciences) > Laboratoire de Dynamique Moléculaire (Sciences)
Leyh, Bernard ; Université de Liège - ULiège > Département de chimie (sciences) > Laboratoire de dynamique moléculaire
Hoxha, A.
Dehareng, Dominique ; Université de Liège - ULiège > Centre d'ingénierie des protéines
Jochims, H.-W.; Freie Universität Berlin > Institut für Physikalische Chemie
Baumgärtel, H.; Freie Universität Berlin > Institut für Physikalische Chemie
Language :
English
Title :
The Vacuum UV Photoabsorption spectrum of Methyl Chloride (CH3Cl) and its perdeuterated Isotopomer CD3Cl. II. A vibrational Analysis.
Alternative titles :
[fr] Le spectre de photoabsorption UV sous vide du Chlorure de Méthyle (CH3Cl) et de son isotopomère CD3Cl. II. Une analyse vibrationnelle.
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