CF4

Report
HIGH RESOLUTION STIMULATED
RAMAN SPECTROSCOPY OF CARBON
TETRAFLUORIDE CF4
V. BOUDON,
Laboratoire Interdisciplinaire Carnot de Bourgogne, UMR 5209 CNRS-Université de Bourgogne, 9. Av. A. Savary, BP 47870, F-21078
Dijon Cedex, France
D. BERMEJO, R. Z. MARTÍNEZ,
Instituto de Estructura de la Materia, CSIC Serrano 123, E-28006 Madrid, Spain
67th Ohio State University Symposium on Molecular Spectroscopy • June 18–22, 2012
Contents
I.
The CF4 molecule
II. Raman experiment
III. The ν1 and 2ν1–ν1 bands
IV. The ν2, 2ν2 and 3ν2–ν2 bands
V.
Conclusions and perspectives
67th Ohio State University Symposium on Molecular Spectroscopy • June 18–22, 2012
I. The CF4 molecule
67th Ohio State University Symposium on Molecular Spectroscopy • June 18–22, 2012
Carbon tetrafluoride (CF4)
CF4 is a strong greenhouse gas (natural and anthropogenic origin)
Global Warming Potential = 6500 (CO2 = 1), lifetime = 50,000 years
Concentration = 75 pptv, annual increase = 1.6 %
Point group Td
ν1
ν2
ν3
ν4
A1
E
F2
F2
Stretching
Bending
Stretching
Bending
Raman
Raman
IR
IR
909 cm-1
435 cm-1
1283 cm-1
631 cm-1
67th Ohio State University Symposium on Molecular Spectroscopy • June 18–22, 2012
CF4 vibrational levels
2ν1–ν1
Coriolis
INFRARED
Boudon et al.,
Mol. Phys. 109,
2273–2290 (2011)
RAMAN: This work
Global analysis
67th Ohio State University Symposium on Molecular Spectroscopy • June 18–22, 2012
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
H Pk  

t
K,n v v'
ss '
all indexes
K,n 
 v v'   (A1g )

 R
 Vss ' 
Parameters
Rotation
Vibration
 All interactions are automatically included
 Vibrational extrapolation
 Global analyses
67th Ohio State University Symposium on Molecular Spectroscopy • June 18–22, 2012
II. Raman experiment
67th Ohio State University Symposium on Molecular Spectroscopy • June 18–22, 2012
Experimental setup in Madrid
Inverse Raman Spectrometer
67th Ohio State University Symposium on Molecular Spectroscopy • June 18–22, 2012
The spectra
135 K
ν1, ν2, 2ν2
296 K
ν1, 2ν1–ν1, 2ν2, 3ν2–ν2
350 K
ν1, ν1+ν2–ν4
Spectral resolution : ca. 0.003 cm–1
67th Ohio State University Symposium on Molecular Spectroscopy • June 18–22, 2012
III. The ν1 and 2ν1–ν1 bands
67th Ohio State University Symposium on Molecular Spectroscopy • June 18–22, 2012
The 2ν1 hot band at 135 K
67th Ohio State University Symposium on Molecular Spectroscopy • June 18–22, 2012
The 2ν1-ν1 hot band at room temperature
67th Ohio State University Symposium on Molecular Spectroscopy • June 18–22, 2012
Fit residuals for line positions
232 assignments
Jmax = 73
St. Dev. = 2.868
dRMS = 0.632 10-3 cm-1
2304 assignments
Jmax = 76
St. Dev. = 2.741
dRMS = 0.471 10-3 cm-1
67th Ohio State University Symposium on Molecular Spectroscopy • June 18–22, 2012
IV. The ν2, 2ν2 and 3ν2–ν2 bands
67th Ohio State University Symposium on Molecular Spectroscopy • June 18–22, 2012
The ν2 band at 134 K
67th Ohio State University Symposium on Molecular Spectroscopy • June 18–22, 2012
The ν2 band at 134 K (details & residuals)
Part of OP branch
Q branch
Part of RS branch
67th Ohio State University Symposium on Molecular Spectroscopy • June 18–22, 2012
The 2ν2 band (A1 sublevel) at 135 K
67th Ohio State University Symposium on Molecular Spectroscopy • June 18–22, 2012
The 3ν2-ν2 hot band at room temperature
Extrapolation from 2ν2 and ν2
Anharmonicity was adjusted manually
67th Ohio State University Symposium on Molecular Spectroscopy • June 18–22, 2012
IV. Conclusions and perspectives
67th Ohio State University Symposium on Molecular Spectroscopy • June 18–22, 2012
The CF4 equilibrium bond length
4
di
Be  B0   Bi
2
i 1
with
Bi  Bi  B0   i
3h
re 
64 2 cM F Be
Using present Raman data for ν1 and ν2 and infrared results
from Boudon et al., Mol. Phys. 109, 2273–2290 (2011) for ν3 and
ν4 , we get:
re  1.315880(53) Å
Ab initio value from Wang et al., J. Chem. Phys. 112, 1353–
1366 (2000): re  1.31526 Å
67th Ohio State University Symposium on Molecular Spectroscopy • June 18–22, 2012
Perspectives for CF4 spectroscopy
• Analysis of new IR spectra: ν1+ν2, ν1+ν4
• Analysis of Raman hot bands: ν1+ν2–ν2, ν1+ν4–ν4
• ν3 and 2ν4 being linked through Coriolis interaction, global
analysis of all IR and Raman bands in the 0–1600 cm–1
region
• Study of hot bands in the ν3 region for atmospheric
applications
• Measurements and analysis of IR intensities or crosssections
67th Ohio State University Symposium on Molecular Spectroscopy • June 18–22, 2012

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