HIGH-RESOLUTION INFRARED AND
RAMAN SPECTROSCOPY OF SF6 :
THE STATE-OF-THE-ART IN JUNE
2006
Vincent BOUDON
Laboratoire de Physique de l’Université de Bourgogne – CNRS UMR 5027, 9 Av. A. Savary, BP 47870, F-21078 Dijon, FRANCE
José Luis DOMÉNECH, Dionisio BERMEJO
Instituto de Estructura de la Materia, CSIC Serrano 123, E- 28006 Madrid, SPAIN
El Bachir MKADMI, Hans BÜRGER, Helge WILLNER
Fachbereich C – Anorganische Chemie, Bergische Universität Wuppertal, D-42097 Wuppertal, GERMANY
Nelly LACOME
LADIR – CNRS UMR 7075, Case Courrier 49, 4 Place Jussieu, F-75252 Paris Cedex 05, France
61th Ohio State University Symposium on Molecular Spectroscopy • June 19–23, 2006
SF6: a greenhouse gas
• Atmospheric abundance ~ 5.8 pptv
• Chemically inert  Atmospheric lifetime ~ 3200 years
• Global warming potential = 23 900  CO2
• Rejected by various industries (electrical, …)
Source: NIST
Absorbance

Hot bands
34SF
920
6
930
940
950
-1
Wavenumber / cm
960
61th Ohio State University Symposium on Molecular Spectroscopy • June 19–23, 2006
Contents
I.
General aspects of SF6 spectroscopy
II. Infrared bands
III. Raman bands
IV. Conclusion & perspectives
61th Ohio State University Symposium on Molecular Spectroscopy • June 19–23, 2006
I. General aspects of
SF6 spectroscopy
61th Ohio State University Symposium on Molecular Spectroscopy • June 19–23, 2006
The SF6 molecule
Normal modes of vibration :
C4
C3






A1g
Eg
F1u
F1u
F2g
F2u
Stretching
Stretching
Stretching
Bending
Bending
Bending
IR
IR
Raman
HyperRaman
948 cm-1
615 cm-1
523 cm-1
347 cm-1
Raman Raman
775 cm-1
Point group: Oh
643 cm-1
Small rotational constant:
Isotopologues in natural
abundance :
32SF
6
33SF
6
95.02 % 0.75 %
34SF
6
36SF
6
4.41 %
0.02 %
61th Ohio State University Symposium on Molecular Spectroscopy • June 19–23, 2006
The vibrational
levels of SF6
Analyzed bands (< 1400 cm-1):
Infrared cold bands:
4
32, 34
3
32, 33, 34
2+6, 2+4
32
Infrared hot bands:
4+6-6
32
Raman cold bands:
1, 2, 5, 6 (A1g) 32, 34
Raman hot bands:
1+6-6, 1+5-5
32, 34
61th Ohio State University Symposium on Molecular Spectroscopy • June 19–23, 2006
The vibrational
levels of SF6
Analyzed bands (> 1400 cm-1):
Infrared cold bands:
3
32
IR–IR double resonance:
3-3
32
Raman–Raman double
resonance:
1-1
32, 34
61th Ohio State University Symposium on Molecular Spectroscopy • June 19–23, 2006
Population of the vibrational levels
61th Ohio State University Symposium on Molecular Spectroscopy • June 19–23, 2006
A (very) few words about theory
• Tensorial effective Hamiltonian:
Parameters
Rotation
(Jx, Jy, Jz)
Vibration
(a, a+)
• Group theory & sublevel splittings:
2(Eg)+6(F2u)
2[3(F1u)]
E g  F2u  F1u  F2u
F1u  F1u   A1g  E g  F2g
F1u
v2 = v6 = 1
1.76 cm-1
F2u
v3 = 2
F2g
7.6 cm-1
Eg
A1g
61th Ohio State University Symposium on Molecular Spectroscopy • June 19–23, 2006
II. Infrared bands
61th Ohio State University Symposium on Molecular Spectroscopy • June 19–23, 2006
The strongly absorbing 3 region
3 itself very well known (H up to order 10 !) but …
Transmission
0.6
0.4
Simulation
0.2
0.0
Experiment
947.5
947.6
947.7
947.8
947.9
-1
Wavenumber / cm
948.0
948.1
61th Ohio State University Symposium on Molecular Spectroscopy • June 19–23, 2006
The 4 region: less dense than 3
FTIR spectrum
recorded in Wuppertal
61th Ohio State University Symposium on Molecular Spectroscopy • June 19–23, 2006
The 2+4 combination band
Overview of the Q-branches region
1.0
0.8
F2u
Transmission
F1u
0.6
Simulation
0.4
0.2
Experiment
0.0
1256
1258
1260
1262
-1
Wavenumber / cm
1264
61th Ohio State University Symposium on Molecular Spectroscopy • June 19–23, 2006
A rich spectrum !
32SF
6
1.2

Transmission
1.0
0.8
FTIR spectrum recorded at LADIR
+
+
0.6
+
++
+
++
+
++
0.4
0.2
0.0
-0.2
+
•
(CF4)
+ ••
 •••
1000
1200
+
1400
-1
Wavenumber / cm
+
+
1600
1800
• Analyzed for 32SF6, • Analyzed for 33SF6, • Analyzed for 34SF6
Similar spectra have been recorded in Wuppertal for 34SF6
61th Ohio State University Symposium on Molecular Spectroscopy • June 19–23, 2006
III. Raman bands
61th Ohio State University Symposium on Molecular Spectroscopy • June 19–23, 2006
Overview of the Raman bands of 32SF6
Stimulated Raman
spectra recorded in Madrid
61th Ohio State University Symposium on Molecular Spectroscopy • June 19–23, 2006
Raman intensity / Arbitrary unit
The 1 region
14
12
32
SF6
10
8
Simulation
1+26-26
1+6-6
1
6
4
2
Experiment
0
772.5
Raman intensity / Arbitrary unit
1+5-5
10
8
6
4
2
773.0
773.5
-1
Wavenumber / cm
774.0
774.5
34
SF6
Simulation
1+5-5
21-1
1+26-26
1+6-6
1
Experiment
0
772.5
Stimulated Raman
spectra recorded in Madrid
773.0
773.5
-1
Wavenumber / cm
774.0
774.5
61th Ohio State University Symposium on Molecular Spectroscopy • June 19–23, 2006
Raman intensity / Arb. unit
Other examples
Simulation
34
SF6

Experiment
630
632
634
636
638
640
SF6 
642
644
646
-1
Wavenumber / cm
1.5
650
652
654
656
32
SF6 26 (A1)
Simulation
1.0
Experiment
0.5
Raman intensity / Arbitrary unit
Raman intensity / Arbitrary unit
34
648
1.5
1.0
Experiment
0.5
0.0
Simulation
0.0
527.6
527.8
528.0 528.2 528.4 528.6
-1
Wavenumber / cm
Stimulated Raman
spectra recorded in Madrid
528.8
529.0
693.0
693.2
693.4
693.6
-1
Wavenumber / cm
693.8
61th Ohio State University Symposium on Molecular Spectroscopy • June 19–23, 2006
IV. Conclusion & perspectives
61th Ohio State University Symposium on Molecular Spectroscopy • June 19–23, 2006
Isotopic shifts and bond length
• Isotopic shifts:
i /
(cm-1.amu-1)
32–34
32–33
1 (A1g)
2 (Eg)
3 (F1u) 4 (F1u) 5 (F2g) 6 (F2u)
–0.0289 –0.0176 +8.7081 +1.3886 –0.0206 –0.0132
–
–
+8.4484
–
–
–
• S–F bond length:
SF6 data  re  0.55604 Å 
  re  0.5560(1) Å
34
SF6 data  re  0.55594 Å 
32
(Ab initio and force field  re  0.5561 Å)
61th Ohio State University Symposium on Molecular Spectroscopy • June 19–23, 2006
Still a lot to do …
• Analyses of 4, 4+6-6 and 2+6 of 34SF6 are under way.
• Analyze more combination and overtone bands (+
+ + )
• Is it possible to reach  experimentaly ?
• Analyze hot bands in the 3 (and 4) region.
• Analyze intensities : difficult, because of line clustering.
61th Ohio State University Symposium on Molecular Spectroscopy • June 19–23, 2006
The HTDS
database
Highly-spherical Top
Data System
www.u-bourgogne.fr/LPUB/shTDS.html
• Molecular parameter database
• Calculation and analysis programs
• XTDS : Java interface
61th Ohio State University Symposium on Molecular Spectroscopy • June 19–23, 2006