Transcript WF16_DAUMONT_CH4_TF.ppt

Long path- High resolution spectrum of methane.
Towards Titan’s Atmosphere
L. Daumont, A. Nikitin, X. Thomas, L. Régalia, Pierre Von der Heyden, V.
Tyuterev, L. Brown.
Titan’s atmosphere is very close to the earth atmosphere:
N2 95%,
CH4 3%,
Ar 2%
T from 70 K to 200 K
~1000 km thickness
pressure (ground) 1.5 atm
Spectral observations: CASSINI, from earth….
HITRAN 2008 database for 12CH4
Laboratory setup available at Reims:
GSMA Original Design
Step by step FT
N2 Cooled cell
Base length: 2 m
Under construction
Room T cell
Base length: 50 m
First series of spectra- long path:
MOPD (cm) 110
L=1600 m T=287 to 290 K
60
78
58
P (torr)
1
f =1m
5
f=3.5 mm
InSb Detector
A
25
Octad
B
Tetradécad
C
Icosad
D
Triacontad
Comparison to JPL spectra (LR Brown -JQSRT 96,251 (2005))
Tetradecad
Icosad
JPL: P=26 torr L=25 m
JPL:
P=6 torr
GSMA: P=25 torr
Triacontad
L=433 m
L=1603 m
Data from the spectral region C: 6287-6550 cm-1
Nikitin et al. JQSRT 112, 28-40 (2011)- 5n4 et n2+4n4, (n1+3n4 et n2+3n4)
Data from spectral region B: 4600-4880 cm-1
Nikitin et al. JMS in Press doi:10.1016/j.jms.2011.04.002 - 2n3 –n4.
Daumont et al. To be submitted- 2 mm Octad band system
Comparison of linelists to experimental spectra
PxL
(torr m)
40 000
Exp: 1600 m 25 torrs
Sim: 433 m 6 torrs
2 598
19 250
Sim: 385 m 50 torrs
Comparison of linelists to experimental spectra 2
Region B, cold
bands of 12CH4
Exp: 1600 m 25 torrs
In the cold bands: 1014/10626 positions, 1095/ 3503 intensities
Wavenumber calibration:
CO2 introduced between the cell and the spectrometer (Miller & Brown).
Region B: 20013 (4853 cm-1) et 20011 (5099 cm-1)
Region C: 30012 (6350 cm-1)
precision < 0.5 mk
Comparisons for intensities:
Région C: 10-20% below CRDS et JPL data
Région B: 10-20% below JPL data
……
Second series of spectra -long path
P=1 torr T=290 K
Detector InSb
MOPD 73 cm
L (m)
200
600
1800
Octade (B)
Tetradécade (B)
New intensities:
Region B:
spectra 200 m and 600 m: 5% below JPL data for lines with intensities around
10-24 cm/molec
Spectrum 1800 m:
……
10% below JPL data for some few lines with intensities
around 10-26 cm/molec
Conclusion:
Data from long-path FTS at room Temperature:
- Completes the previous experimental data for weak lines.
- Allow to determine many parameters of the effective hamiltonian
and dipole moment usefull to extrapolate data to low temperature.
- Will be used with future data at low temperature (~100 K) make
assignments easier