Line Positions and Intensities
for the ν12 Band of 13C12CH6
V. Malathy Devi1, D. Chris Benner1, Keeyoon Sung2,
Timothy J. Crawford2, Arlan W. Mantz3, and Mary Ann H. Smith4
1The
College of William and Mary, Williamsburg, VA 23187, U.S.A.
2Science Division, Jet Propulsion Laboratory, California Institute of Technology,
Pasadena, CA 91109, U.S.A.
3Dept. of Physics, Astronomy and Geophysics, Connecticut College,
New London, CT 06320, U.S.A.
4Science Directorate, NASA Langley Research Center, Hampton, VA 23681, U.S.A.
FE08-69th International Symposium on Molecular Spectroscopy, June 16-20, 2014
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Ethane in Earth and Planetary Atmospheres
The most abundant ethane isotopologue, 12C2H6, is easily detected in spectra
of Earth and planetary atmospheres and in comet volatiles.
 13C12CH6 appears in atmospheric spectra of Jupiter, Saturn, Neptune and Titan.
 Spectral observations of both isotopologues at 12 µm enable 13C/12C ratios to be
determined for Jupiter, Saturn, and Titan.
Recent high-resolution studies to improve 12-µm ethane parameters:
ν9 band [Malathy Devi et al., JQSRT 111 (2010) 1234-1251; Malathy Devi et al., JQSRT 111
(2010) 2481-2504 and references therein] updated in HITRAN 2012.
12C
2 H6
ν12 based on Kurtz et al. (1991) and Weber et al. (1993,1994) in GEISA 2009 ; more recent
ν12 and ν12+ν6−ν6 positions and assignments [Borvayeh et al., J. Mol. Spectrosc. 255 (2009) 157-163;
Moazzen-Ahmadi et al., JQSRT 129 (2013) 316-323] not yet in GEISA or HITRAN.
13C12CH
6
Using low-temperature spectra to minimize hot-band transitions, we have
measured line positions and absolute intensities for 1660 ν12 transitions.
FE08-69th International Symposium on Molecular Spectroscopy, June 16-20, 2014
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13C12CH
6
in the spectrum of Jupiter
P.V. Sada, G.H. McCabe, G.L. Bjoraker, D.E. Jennings, D.C. Reuter. Astrophys. J. 472 (1996) 903-907.
FE08-69th International Symposium on Molecular Spectroscopy, June 16-20, 2014
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Recording the Spectra
 The spectra of 13C12CH6 were recorded with the 20.38 cm coolable cell [Sung et al., J.
Mol. Spectrosc. 262 (2010) 122-134] installed inside the sample compartment of the Bruker IFS
125 HR spectrometer at JPL. The cell body is oxygen free high conductivity (OFHC) copper
with wedged ZnSe windows; the vacuum shroud box has wedged KBr windows.
• KBr beamsplitter, MCT detector, resolution ~0.003 cm-1
• Temperatures: 130 K, 178 K, 208 K, and 294 K.
• Total pressures: 2 – 5 torr (2.7 – 6.7 hPa) at 130 – 208 K; 9.5 torr (12.6 hPa) at 294 K.
• Gas sample: 13C-enriched ethane (13C, 99%) from Cambridge Isotope Labs.
FE08-69th International Symposium on Molecular Spectroscopy, June 16-20, 2014
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Laboratory spectra of 13C12CH6 at two temperatures
a
1 atm = 101.3 kPa = 760 Torr
FE08-69th International Symposium on Molecular Spectroscopy, June 16-20, 2014
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Laboratory spectra of 13C12CH6 at two temperatures
RQ(J,7)
RQ(J,8)
● RR(5,4)
a
● RR(6,5)
1 atm = 101.3 kPa = 760 Torr
FE08-69th International Symposium on Molecular Spectroscopy, June 16-20, 2014
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Multispectrum Fitting Analysis
 Only the 4 low-temperature spectra 130–208 K were included in the fits to minimize
interferences from weak high-J and hot-band transitions. Short spectral intervals (1‒3
cm−1) were fit in all 4 spectra simultaneously.
 Important: All spectra are calibrated to the same reference standard (H2O ν2 line
positions [R.A.Toth, J. Opt. Soc. Am. B 8 (1991) 2236-2255]).
 Initially 13C12CH6 line list from GEISA 2009 (also available as a supplement to
HITRAN 2008). Weak features missing from the original list were added interactively.
 HITRAN partition functions [A. L. Laraia et al., Icarus 215 (2011) 391-400] were applied
in the fitting algorithm to obtain corresponding line intensities at 296 K.
 Intensity ratios of torsionally split components and their separations, were at first
constrained to predicted values, but some were later adjusted in the fitting process.
 Lorentz half-width, pressure-induced shift coefficients and their temperature
dependences were fixed to appropriate default values using 12C2H6 measured values
[Malathy Devi et al., JQSRT 111 (2010) 1234-1251; JQSRT 111 (2010) 2481-2504].
FE08-69th International Symposium on Molecular Spectroscopy, June 16-20, 2014
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Observed torsional splitting in ν12 of
13C12CH ,
6
FE08-69th International Symposium on Molecular Spectroscopy, June 16-20, 2014
2 Torr at 130 K
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13C12CH
6
multispectrum fit and residuals
4 self-broadened spectra
The same color codes are
used for the observed
spectra and residuals:
Red
Blue
Green
Black
PP
(2.05 Torr at 130 K)
(4.99 Torr at 178 K)
(2.95 Torr at 178 K)
(4.94 Torr at 208 K)
transitions
Torsional splitting not resolved
FE08-69th International Symposium on Molecular Spectroscopy, June 16-20, 2014
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13C12CH
6
multispectrum fit and residuals
4 self-broadened spectra
The same color codes are
used for the observed
spectra and residuals:
Red (2.05 Torr at 130 K)
Blue (4.99 Torr at 178 K)
Green (2.95 Torr at 178 K)
Black (4.94 Torr at 208 K)
PP, RP,
and PQ transitions
Torsional splitting not resolved
FE08-69th International Symposium on Molecular Spectroscopy, June 16-20, 2014
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13C12CH
6
multispectrum fit and residuals
4 self-broadened spectra
The same color codes are
used for the observed
spectra and residuals:
Red
Blue
Green
Black
PP, RP,
(2.05 Torr at 130 K)
(4.99 Torr at 178 K)
(2.95 Torr at 178 K)
(4.94 Torr at 208 K)
and PQ transitions
Torsional splitting is resolved
for high-J PQ(K=6) lines
FE08-69th International Symposium on Molecular Spectroscopy, June 16-20, 2014
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13C12CH
6
multispectrum fit and residuals
4 self-broadened spectra
The same color codes are
used for the observed
spectra and residuals:
Red
Blue
Green
Black
PR
(2.05 Torr at 130 K)
(4.99 Torr at 178 K)
(2.95 Torr at 178 K)
(4.94 Torr at 208 K)
and RR transitions
Torsional splitting is resolved
only for PR(18,6) line ~830.1 cm-1
FE08-69th International Symposium on Molecular Spectroscopy, June 16-20, 2014
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Results
Four spectra recorded at 130 to 208 K were included in the analysis.
Of the 2948 spectral lines measured, 34% were weak, unidentified
features; however, approximate lower state energies could be estimated
for some of these lines.
15% of the remaining ν12 transitions were not reported because of
blends or unsatisfactory fits.
Line positions and intensities are reported for 1660 ν12 transitions of
13C12CH with known assignments.
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• Positions accurate to ± 1 to 4 × 10−4 cm−1
• Intensities accurate to ± 2 to 3%
Good agreement with HITRAN 2008, but not HITRAN 2012.
[13C12CH6 intensities in HITRAN 2012 were inadvertently re-scaled by the same
factor (−15%) as those for 12C2H6.]
FE08-69th International Symposium on Molecular Spectroscopy, June 16-20, 2014
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ν12 Positions and Intensities Compared to
HITRAN08 Supplement (same as GEISA09)
13C12CH
6
Most position differences
are within ± 0.0005 cm−1
PS/HITRAN08 intensity
ratio Mean ± Standard
Deviation: 1.09 ± 0.10
To agree with the
present study, the
13C12CH ν intensities
6 12
in HITRAN 2012 should
be scaled by 1.28
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Summary
From multispectrum fits of low-temperature (130 – 208 K)
spectra we have determined
• Line positions and absolute intensities for 1660 ν12
transitions of 12C13CH6.
• Positions and intensities for approximately 1000 other
unassigned lines in the 12.2 µm region.
• Approximate lower state energies for some of these
unassigned lines.
Results were recently published:
V. Malathy Devi et al., J. Mol. Spectrosc. 301 (2014) 28-38.
http://dx.doi.org/10.1016/j.jms.2014.05.005
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The Team and Acknowledgements
Malathy
Keeyoon
Linda
Tim
Arlan
Mary Ann
Chris
Acknowledgements
Research described in this talk was performed at Connecticut College, the College of William
and Mary, NASA Langley Research Center and the Jet Propulsion Laboratory, California
Institute of Technology, under contracts and cooperative agreements with the National
Aeronautics and Space Administration. We thank Linda Brown for technical assistance and
helpful comments.
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