64th Ohio State University Symposium on Molecular Spectroscopy June 22–26, 2009 THE HIGH RESOLUTION FAR- INFRARED SPECTRUM OF METHANE AT THE SOLEIL SYNCHROTRON.

64th Ohio State University Symposium on Molecular Spectroscopy • June 22–26, 2009

THE HIGH RESOLUTION FAR-INFRARED SPECTRUM OF METHANE AT THE SOLEIL

SYNCHROTRON

THE HIGH RESOLUTION FAR-INFRARED SPECTRUM OF METHANE AT THE SOLEIL

SYNCHROTRON

Vincent BOUDONInstitut Carnot de Bourgogne – UMR 5209 CNRS-Université de Bourgogne, 9 Av. A. Savary, BP 47870, F-21078 DIJON, France

Olivier PIRALI, Pascale ROYLigne AILES – Synchrotron SOLEIL, L’Orme des Merisiers, F-91192, GIF-SUR-YVETTE, France

Laurent MANCERONLADIR – UMR 7075 Université Pierre et Marie Curie–CNRS, Case 49, 4 Place Jussieu, F-75252 PARIS, France

Jean VANDER AUWERAService de Chimie Quantique et Photophysique, ULB, CP 160/09, 50 Av. F. D. Roosevelt, F-1050 BRUSSELS, Belgium


ContentsContents

I. The THz spectrum of CH4

II. Experimental details

III. Analysis of line intensities

IV. Conclusion


I. The THz spectrum of CH4I. The THz spectrum of CH4


The polyads of CH4The polyads of CH4


Centrifugal distortion spectrumCentrifugal distortion spectrum• CH4 has no permanent dipole moment

• Due to the contact transformation, the effective dipole moment up to 1st order expands as (for cold and hot bands):

• These parameters can be calculated analytically (Hilico et al. 1987, Loëte 1988)

μ GS−GS = μ GS−GS{ }

GS−GS = μ 0R2 2,F2( ) + ...

μ Dyad−Dyad = μ GS−GS{ }

Dyad−Dyad +μ ν 2 −ν 4{ }

Dyad−Dyad +μ ν 4 −ν 4{ }

Dyad−Dyad

= μ 0R2 2,F2( ) +μ 2,4V2,4

EF2 F2( ) +μ 4,4V4,4F2F2 F2( ) + ...

μ D = 8μ 0R2 2,F2( ) is the centrifugal distorsion term


Far-infrared CH4 lines on TitanFar-infrared CH4 lines on Titan5x10-7

4x10-7

3x10-7

2x10-7

1x10-7

0x10-7

1400120010008006004002000Wavenumber / cm-1

CH4 (ν4)C2H4

C2H4

C2H2

HCN

CO2

C4H2C3H4

CH4 ( )GS

1601401201008060

J = 67

8 9 10 11

/ Cassini CIRS 32Flyby T

50°Latitude N = 0.5 Resolution cm-1

: . ( )Courtesy A Coustenis LESIA

12


Previous worksPrevious works

1988: First resolved spectraCourtesy A. R. W. McKellarUnpublished resultsP ~ 36 Torr, T ~ 128 K, Path ~ 20 m Resolution ~ 0.008 cm-1

• R branch measured at low resolution and high pressure: Ozier and Rozenberg (1975, 1978)

• Q branch measured in microwave: Holt et al. (1975), Oldani et al. (1985) – no intensities

• Theoretical calculation of Hilico et al. (1987), Loëte (1988)

• R branch reinvestigated by Wishnow et al. (2007), but still at low resolution and high pressure (≥ 1 bar)


Calculation using STDSCalculation using STDS2.5x10-7

2.0x10-7

1.5x10-7

1.0x10-7

1601401201008060Wavenumber / cm-1

CIRS

Simulation

J = 6 7 8 9 10 11 12


II. Experimental detailsII. Experimental details


AILES beamline at SOLEILAILES beamline at SOLEILHigh Resolution Absorption Spectroscopy in the Far-IR

Synchrotron beam entrance

Interferometer

Multipass cell :

Max = 200m

Bolometer detectors

Maximum spectral resolution = 0.001 cm-1

Spectral range= 7-1000 cm-1

See Talk TG04


Experimental conditionsExperimental conditions

Multipass White cell: L = 151.748 mAmbiant temperature (T = 296 K)

Pressure / mb 9.91 20.0 50.0 100.0

Resolution / cm-1 0.0011 0.002 0.005 0.010


Examples of resolved rotational clustersExamples of resolved rotational clusters1.0

0.9

0.8

0.7

0.6

0.5125.4125.2125.0124.8124.6

Wavenumber / cm-1

8

7

6

5

4

3

R(11) regionSimul. (cold band only)Simul. (with hot bands)H2O (Hitran 04)Experiment



0.95

0.90

0.85

0.80

0.75

0.70165.9165.8165.7165.6165.5165.4165.3165.2

Wavenumber / cm-1

3.0

2.8

2.6

2.4

2.2

2.0

1.8

1.6

R(15) regionSimul. (cold band only)Simul. (with hot bands)H2O (Hitran 04)Experiment



1.0

0.8

0.6

0.4

0.2

0.0

135.5135.4135.3135.2135.1135.0134.9Wavenumber / cm-1

R(12) region

Simulation 10 mb 20 mb 50 mb

Experiment 10 mb 20 mb 50 mb

|H2O


III. Analysis of line intensitiesIII. Analysis of line intensities


Measurements vs. HITRAN for R(7)Measurements vs. HITRAN for R(7)1.0

0.9

0.8

0.7

0.6

0.58786858483828180

Wavenumber / cm-1

Obs Wishnow (Hitran08) Hitran 04 Hitran 08

1.00.90.80.70.60.5

83.6283.6083.5883.56Wavenumber / cm-1

Obs Wishnow (Hitran08) Hitran 04 Hitran 08


Fit details: 1st order dipole momentFit details: 1st order dipole moment

0 cm-1

1310 cm-1

1533 cm-1 ν2

ν4

Dyad, Hot bands: 114 lines

Ground State, Cold band: 100 lines

μ GS−GS{ }

Dyad−Dyad ≡ μ GS−GS{ }

GS−GS

Three different fits:

1.GS – GS (cold band) alone2.GS – GS and Dyad – Dyad (cold and hot bands) simultaneously3.Dyad – Dyad (hot band) alone with GS – GS parameter fixed to result of fit 1.


Fit residuals for the GS–GS fit (fit 1)Fit residuals for the GS–GS fit (fit 1)


Fit residuals for the simultaneous fit (fit 2)Fit residuals for the simultaneous fit (fit 2)1.94


Comparison of the different resultsComparison of the different results

Fit Nb. data σ dRMS /% μ2 2,F2( ) / μD μD / μD μ2,4 / mD μ4,4 / mD

1 100 1.894 11.91 8.273(38) 23.40(11) − −2 100 /114 1.940 / 2.771 11.99 /11.98 8.045(49) 22.75(14) 7.22(26) −37.48(21)

3 114 2.786 11.97 8.273* 23.40* 7.23(30) −37.48(24)Hilico (calc.) − − 7.90 22.34 10.8 −34.7

Wishnow 3** − − − 23.82(88) − −23.9(1.2)

* = fixed, * * = unresolved clusters

Fit Intensity factor compared to HITRAN 20041 1.0972 1.037

Wishnow 1.154

NB: Factor 1.154 has been applied to HITRAN 2008


IV. ConclusionIV. Conclusion


What is the “correct” value for μD?What is the “correct” value for μD?

• The calculated value (Hilico et al. 1987) is certainly too low

• The GS–GS fit of high-resolution data gives a slightly lower value than Wishnow et al. (2007)

• The simultaneous fit of cold and hot bands lowers the μD value, but there maybe some other contributions to take into account for the hot band (higher RMS)

• μD only contributes marginally to the hot band intensity

• We thus recommend μD = 23.40 ×10-6 D ; but measured intensities can now be used (to be published)


The STDS databaseThe STDS database

Spherical Top Data System

www.icb.cnrs.fr/OMR/SMA/SHTDS

• Molecular parameter database

• Calculation and analysis programs

• XTDS : Java interface

64th Ohio State University Symposium on Molecular Spectroscopy June 22–26, 2009 THE HIGH RESOLUTION FAR- INFRARED SPECTRUM OF METHANE AT THE SOLEIL SYNCHROTRON.

Documents

molecular spectroscopy

conclusion slide

bar slide

titan slide

stds slide

belgium slide

tg04 slide

low resolution