. 1 MJ03 65 th Molecular Spectroscopy Symposium, Columbus, OH, June 2010 High Resolution Investigation of the Ethane Spectrum at 7 Micron (1430 cm -1 )

. 1 MJ03 65th Molecular Spectroscopy Symposium, Columbus, OH, June 2010

High Resolution Investigation of the Ethane Spectrum at 7 Micron (1430 cm-1)

Carlo di Lauro, Franca Lattanzi Dipartimento di Chimica Farmaceutica e Tossicologia,

Universita di Napoli Federico II , I-80131 Naples, Italy

Keeyoon Sung, Linda R. Brown Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA

Jean Vander Auwera Service de Chimie Quantique et Photophysique, Universite Libre de Bruxelles,

CP 160/09, 50 avenue F.D.Roosevelt, B-1050 Brussels, Belgium

Arlan W. MantzDept. of Physics, Astronomy and Geophysics, Connecticut College, New London, CT 06320, USA

Mary Ann H. Smith Science Directorate, NASA Langley Research Center, Hampton, VA 23681, USA


Ethane is abundant in planetary atmospheres

Ethane Has 12 fundamentals but only 5 are IR active.


New GOSAT-2009 line list in HITRAN format

C2H6 ν8 Q branches are prominent in Titan:

► The spectrum of Titan at 0.5 cm–1 resolution (apodized) recorded by the CIRS FTIR on the Cassini spacecraft. ► Dotted line: calculated spectra using CH4 (HITRAN

2004) and C2H6 (based on

PNNL cross sections).► Our goal: obtain C2H6 line positions and intensities to create the first HITRAN-like database for this region.


C2H6 spectra at cold and room temperatures

► Red: room temperature Brussels 294 K (0.063 hPa, 13.80 m, MOPD = 450 cm) ► Blue: cold temperature JPL 131 K (1.3 hPa, 0.204 m, MOPD = 324 cm)

Right: Expanded view provides direct visual indication of high J (↔) transitionsand the ν4 + ν8 - ν4 hot band (↑)

◊ The random strong features are from residual H2O inside the evacuated FTS.

↑↔

◊◊

ν6

ν8

ν4+ν12

2ν4+ν9

◊◊

◊

◊◊◊

◊◊

◊

◊


Expanding Prior Analyses of 12C2H6 Statese.g. F. Lattanzi et al. , J. Mol. Spectrosc. 248 (2008)

► The 7 μm region of ethane contains four fundamentals plus two combination states and two components of an overtone. ► This results in a high density of transitions involving rotation-torsion structure, further complicated by hot bands arising from the ν4 state at 289 cm-1.

Vib.Band

Type &Vib Sym

Center (cm-1)

ν4+ν12┴ IR Eu

1480.61

ν8 ┴ IR Eu

1471.76

ν11 Raman Eg 1468

6ν4

Raman E3s Raman E3d

1429 1358

ν2 Raman A1g 1397

2ν4+ν9┴ IR Eu

1388

ν6 ║ IR A1u 1379.15


Experimental Details: high resolution FTIR

FTS and Gas conditions JPL: Cold TempBruker 125 HR

Brussels: Room Temp Bruker 120 HR

Light Source Glower GlowerBeam Splitter KBr KBrDetector MCT MCTResolution (unapodized) 0.0028 cm-1 0.0021 cm-1

Normal Samples C2H6 C2H6

Sample Pressure (hPa) 1.3 0.065, 0.11, 0.30Path length (cm) 20.4 1380 Temperature (K) 131, 150 294Useable Band Pass (cm-1) 1240 – 1850 878 - 1755

Calibration Standards Residual H2O N2OPosition precisions 0.0003 cm-1 0.0003 cm-1

Over 12000 positions from room temperature data


► Upper left: One hot band ν4 + ν8 - ν4 easily identified

► Lower left: level crossings at high J create band head in PQ1

► Right panels: O- and S-type forbidden lines

New modeling permitted further assignments of greatly perturbed Q branches of ν8!


► R-lines of ν8, with two perturbation-activated t-transitions to ν6

with ΔK=3 (underlined and marked by a star).

► ↔ anomalous J- pattern of rQ16 and its eventual turn is caused by the same interaction, with K=19 in ν6 and 17 in ν8.

New assignments at much higher J

↔

cm-1

..


► arises from nearly constant torsional splitting and K-splitting (increasing with J).

► the (–l), K=2 levels are split by the l(2,–1) interaction with the (+l), K=1 levels [also affected by l(2,2)-doubling].

► The split components K± correspond to upper state wavefunctions

√2 (ΨJKl ± ΨJ–K–l) with K=2 and l = –1.

pQ3 of ν8 split into 4 components by interaction

► K- components: marked above spectrum► K+ components: marked below spectrum►The J-spacing decreases with increasing J leading to a bandhead in the K– subset.

(h = hot transition, w = water line)

.


► left: level crossings between ν8 and ν6

► right: no transitions of 3-quanta band assigned (yet)

Interaction schemes at higher K


Effects of perturbation on rotational constant B

►The strong perturbation within ν8 levels is illustrated using the effective rotational constants B, as determined from ν8 transitions.

► These points should fall on one smoothly varying line.

► The values for levels linked by the l (2,–1) interaction (connected by straight lines) show opposite deviations from the patterns at high | Kl |.

Effective B-values for ν8


Global Hamiltonian (so far)

Vibs. ν6 ν8 ν4+ν12 2ν4+ν9

ν6E C C

ν8 CE

l(2,2)

F l(2,-1)

l(2,-1)

ν4+ν12F

l(2,-1)E

l(2,-1) l(2,2)

2ν4+ν9 C l(2,-1)E

l(2,2)


Assigned IR lines of C2H6 at 7 microns

Band cm-1 K max J max Assigned ΔK=-2 ΔK=+2 ΔK=3

ν4+ν12 1480.749 4 30 371

ν8 1471.837 20 39 3415 206 168

2ν4+ν91388 ?

ν6 1379.150 10 31 613 6

ν4+ν8 - ν4 1471.915 11 998

rmscm-1

Cold bands:

0.0038 4399

rmscm-1

Hot band

0.012 998


Calculated vs observed ethane spectra

► Red: observed at 294 K (0.065 hPa)

► Blue: predicted ν8, ν6, ν4 + ν12

► green: hot band: ν4 + ν8 - ν4

The random strong features are residual H2O inside the evacuated FTS.

►transitions moments:

ν8 and ν6 from selected line intensities,

ν4 + ν12 (solely from borrowing)

ν4 + ν8 - ν4 Boltzmann scaling

► Preliminary linelist will have some calculated positions replaced with observed line centers.

► Line intensities (still in progress).


Importance of ethane isotopologues


CONCLUSION

These new linelists with lower states energies ► Characterize the line-by-line spectrum

► Improve molecular databases for planetary remote sensing

Future work ► Additional experimental efforts and theoretical analyses to understand the whole spectrum and provide reliable prediction of molecular line parameters for remote sensing of planetary atmospheres. ► This study is one important step toward this ultimate goal.

JVDA acknowledges financial support from the Fonds de la Recherche Scientifique (FRS-FNRS, Belgium, contracts FRFC and IISN), and the Actionde Recherches Concertées of the Communauté française de Belgique. Part of the research described in this paper was performed at the Jet Propulsion Laboratory, California Institute of Technology, Connecticut College, and NASA Langley under contracts and grants with the National Aeronautics and Space Administration.


Interaction at low K-values.

► Fermi resonance of ν8 and ν4+ ν12, shown for +l.

► l(2,-1) resonance within ν8, dashed lines; shown for those pairs where lines with ΔK=±2.The mechanism by which the l (2,2) splitting of K=1,+l is transmitted (by l(2,-1) resonance to K=2,-l, (in PQ3).

► x,y-Coriolis coupling of ν6 and 2ν4+ ν9: large torsional splitting (~ 3 cm-1) causes a detectable splitting in ν6 for K= 3, 4, 5.

. 1 MJ03 65 th Molecular Spectroscopy Symposium, Columbus, OH, June 2010 High Resolution Investigation of the Ethane Spectrum at 7 Micron (1430 cm -1 )

Documents

ir e u

usa slide

raman e g

s raman e

room temperature data

room temperature brussels

high resolution ftir

high resolution investigation