SF 6 THE FORBIDDEN BAND UNVEILED V BOUDON
SF 6 THE FORBIDDEN BAND UNVEILED V. BOUDON, Laboratoire Interdisciplinaire Carnot de Bourgogne, UMR 5209 CNRS-Université de Bourgogne, 9. Av. A. Savary, BP 47870, F-21078 Dijon Cedex, France L. MANCERON, Ligne AILES – Synchrotron SOLEIL, L’Orme des Merisiers, F 91192 Gif-sur-Yvette, France and Institut des Sciences Moléculaires d’Orsay, UMR 8214 CNRS-Université Paris-Sud, Bât. 210, 91405, Orsay Cedex, France F. KWABIA-TCHANA, Laboratoire Interuniversitaire des Systèmes Atmosphériques, UMR CNRS 7583, Université Paris-Est Créteil et Université Paris. Diderot, 61 Avenue du Général de Gaulle, 94010 Créteil Cedex, France P. ROY, Ligne AILES – Synchrotron SOLEIL, L’Orme des Merisiers, F-91192 Gifsur-Yvette, France 68 th Ohio State University Symposium on Molecular Spectroscopy • June 17– 21, 2013
Contents I. The SF 6 molecule and its ν 6 mode II. Far-IR spectroscopy at SOLEIL III. Theoretical model IV. Band analysis and simulation V. Perspectives for SF 6 hot bands 68 th Ohio State University Symposium on Molecular Spectroscopy • June 17– 21, 2013
I. The SF 6 molecule and its ν 6 mode 68 th Ohio State University Symposium on Molecular Spectroscopy • June 17– 21, 2013
Sulfur hexafluoride (SF 6) Normal modes of vibration : C 4 C 3 Point group: Oh ν 1 ν 2 ν 3 ν 4 ν 5 ν 6 A 1 g Eg F 1 u F 2 g F 2 u Stretching Bending Raman IR IR Raman Inactive 775 cm-1 643 cm-1 948 cm-1 615 cm-1 523 cm-1 347 cm-1 Small rotational constant: B 0 ≈ 0. 091 cm– 1 v 6 = 1 is the lowest vibrational level and thus generates hot bands. But the ν 6 fundamental band is, in first approximation, inactive. 68 th Ohio State University Symposium on Molecular Spectroscopy • June 17– 21, 2013
Vibrational level population 68 th Ohio State University Symposium on Molecular Spectroscopy • June 17– 21, 2013
Observing ν 6? Hypothesis: ν 4 / ν 6 Coriolis interaction Prediction for ν 6 intensity: 6 orders of magnitude lower than ν 3 68 th Ohio State University Symposium on Molecular Spectroscopy • June 17– 21, 2013
II. Far-IR spectroscopy at SOLEIL 68 th Ohio State University Symposium on Molecular Spectroscopy • June 17– 21, 2013
AILES beamline at SOLEIL High Resolution Absorption Spectroscopy in the Far-IR Interferometer Synchrotron beam entrance Multipass cell Bolometer detectors Maximum spectral resolution = 0. 001 cm-1 Spectral range= 7 -1000 cm-1 68 th Ohio State University Symposium on Molecular Spectroscopy • June 17– 21, 2013
Coolable log-path gas cell Accurate far infrared high resolution spectra of diluted gas samples and mixture at temperatures : 400 – 90 K Four compartment chamber: • Sample gas • Convection-cooling gas (He) • Liquid Nitrogen reservoir • Insulating vacuum 1 m Adapted optics for long path ( < 150 m) 68 th Ohio State University Symposium on Molecular Spectroscopy • June 17– 21, 2013
III. Theoretical model 68 th Ohio State University Symposium on Molecular Spectroscopy • June 17– 21, 2013
Theoretical model – Tensorial formalism Systematic expansion of effective Hamiltonian and transition moment up to any order and for any polyad scheme, thanks to group theory and tensorial methods Parameters Rotation Vibration All interactions are automatically included Vibrational extrapolation Global analyses 68 th Ohio State University Symposium on Molecular Spectroscopy • June 17– 21, 2013
Perturbation-induced dipole moment • • Coriolis interaction between ν 6 and ν 4 does not give convincing results There must be a more complicated interaction pattern Anyway, contact transformation induces new terms in the dipole moment We can explain the ν 6 structure with a degree one rotational dipole moment operator (Herman-Wallis type), then considering the band as isolated: This term leads to a complex branch structure, which we do observe! 68 th Ohio State University Symposium on Molecular Spectroscopy • June 17– 21, 2013
The ν 6 complex branch system 68 th Ohio State University Symposium on Molecular Spectroscopy • June 17– 21, 2013
IV. Band analysis and simulation 68 th Ohio State University Symposium on Molecular Spectroscopy • June 17– 21, 2013
The ν 6 band at high-resolution: overview 68 th Ohio State University Symposium on Molecular Spectroscopy • June 17– 21, 2013
The ν 6 band at high-resolution: P branch 68 th Ohio State University Symposium on Molecular Spectroscopy • June 17– 21, 2013
The ν 6 band at high-resolution: Q branch 68 th Ohio State University Symposium on Molecular Spectroscopy • June 17– 21, 2013
The ν 6 band at high-resolution: R branch 68 th Ohio State University Symposium on Molecular Spectroscopy • June 17– 21, 2013
Fit results: seven ν 6 parameters determined 68 th Ohio State University Symposium on Molecular Spectroscopy • June 17– 21, 2013
Detail in the branch structure (I) 68 th Ohio State University Symposium on Molecular Spectroscopy • June 17– 21, 2013
Detail in the branch structure (II) 68 th Ohio State University Symposium on Molecular Spectroscopy • June 17– 21, 2013
Energy levels Good sampling of all branches 68 th Ohio State University Symposium on Molecular Spectroscopy • June 17– 21, 2013
V. Perspectives for SF 6 hot bands 68 th Ohio State University Symposium on Molecular Spectroscopy • June 17– 21, 2013
Toward hot band elucidation • The ν 3+ν 6 level is not accessible (too weak Raman band) • ν 3+ν 6–ν 4 difference band could be observed (and ν 4 is well known), but is very weak in a difficult spectral region • ν 3+ν 2–ν 2 and ν 3+ν 1–ν 1 already done! 68 th Ohio State University Symposium on Molecular Spectroscopy • June 17– 21, 2013
- Slides: 24
